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<title>SDL2 Devlog</title>
<description>&lt;p&gt;I have been working on an editor for the &lt;a href="https://git.peppe.rs/graphics/obi/about"&gt;One Bit Image&lt;/a&gt; file format in Rust and SDL2. This entry in my blog follows my progress on the editor. The days are listed in reverse chronological order, begin from the bottom, if this is your first time on this page.&lt;/p&gt;
&lt;h3 id="day-20"&gt;Day 20&lt;/h3&gt;
&lt;p&gt;More &lt;code&gt;lisp&lt;/code&gt; stuff! I added a new brush, for rectangular selections. While selection doesn’t do much on its own, the selected area can be passed onto a &lt;code&gt;lisp&lt;/code&gt; procedure, for example, a procedure to draw horizontal black and white lines:&lt;/p&gt;
&lt;figure&gt;
&lt;video src="https://u.peppe.rs/frU.mp4" controls=""&gt;&lt;a href="https://u.peppe.rs/frU.mp4"&gt;Day 20&lt;/a&gt;&lt;/video&gt;&lt;figcaption aria-hidden="true"&gt;Day 20&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-19"&gt;Day 19&lt;/h3&gt;
&lt;p&gt;Attempted &lt;a href="https://peppe.rs/art/conduit.png"&gt;some isometric art&lt;/a&gt; within the editor. The angles displayed alongside the line brush are handly, however, having only a rectangular grid did not help. I implemented an isometric grid today. Isometric grids in pixel art differ in that the tangent of the isometric angle is exactly 0.5! For every pixel down, you go exactly two pixels sideways. The math works out really well in the drawing procedures too, dealing with floating points is a pain.&lt;/p&gt;
&lt;figure&gt;
&lt;img src="https://u.peppe.rs/1Kb.png" alt="Day 19" /&gt;&lt;figcaption aria-hidden="true"&gt;Day 19&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-18"&gt;Day 18&lt;/h3&gt;
&lt;p&gt;I added basic support for guides, they can be added and activated from the &lt;code&gt;lisp&lt;/code&gt; REPL. Another long standing improvement I wanted to make was reworking the pixmap drawing procedure. The old procedure draws a square for each pixel in the pixmap, coloured according to its value in the pixmap. Naturally, this means, for an &lt;strong&gt;NxN&lt;/strong&gt; pixmap, there are &lt;strong&gt;N²&lt;/strong&gt; calls to SDL! I reworked this procedure to compress each line of the pixmap using RLE (run length encoding), and call out to SDL for each run in the line. This drastically improved drawing speeds on larger grids. The following is a comparison between the two procedures, the leftmost picture is the rendered image, the middle picture is the optimized drawing procedure (draws each run instead of pixel), and the right most picture is the primitive drawing procedure (draws each pixel):&lt;/p&gt;
&lt;figure&gt;
&lt;img src="https://u.peppe.rs/U4B.png" alt="Day 18" /&gt;&lt;figcaption aria-hidden="true"&gt;Day 18&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-17"&gt;Day 17&lt;/h3&gt;
&lt;p&gt;I decided to give the text-only statusline a touch up, by adding a active color and dither level preview. Aligning the “widget” to the right of statusline involved a lot more than I thought, so I created a ghetto CSS-like rectangle placement system to position containers inside containers:&lt;/p&gt;
&lt;div class="sourceCode" id="cb1"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb1-1"&gt;&lt;a href="#cb1-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// roughly something like this&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-2"&gt;&lt;a href="#cb1-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;let&lt;/span&gt; statusline &lt;span class="op"&gt;=&lt;/span&gt; &lt;/span&gt;
&lt;span id="cb1-3"&gt;&lt;a href="#cb1-3" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="pp"&gt;Container::&lt;/span&gt;new(&lt;span class="pp"&gt;Offset::&lt;/span&gt;Left(&lt;span class="dv"&gt;0&lt;/span&gt;)&lt;span class="op"&gt;,&lt;/span&gt; &lt;span class="pp"&gt;Offset::&lt;/span&gt;Bottom(&lt;span class="dv"&gt;40&lt;/span&gt;))&lt;/span&gt;
&lt;span id="cb1-4"&gt;&lt;a href="#cb1-4" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="op"&gt;.&lt;/span&gt;width(&lt;span class="pp"&gt;Size::&lt;/span&gt;Max)&lt;/span&gt;
&lt;span id="cb1-5"&gt;&lt;a href="#cb1-5" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="op"&gt;.&lt;/span&gt;height(&lt;span class="pp"&gt;Size::&lt;/span&gt;Absolute(&lt;span class="dv"&gt;20&lt;/span&gt;))&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-6"&gt;&lt;a href="#cb1-6" aria-hidden="true"&gt;&lt;/a&gt;    &lt;/span&gt;
&lt;span id="cb1-7"&gt;&lt;a href="#cb1-7" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;let&lt;/span&gt; &lt;span class="kw"&gt;mut&lt;/span&gt; primary &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="pp"&gt;Container::&lt;/span&gt;uninit()&lt;/span&gt;
&lt;span id="cb1-8"&gt;&lt;a href="#cb1-8" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="op"&gt;.&lt;/span&gt;width(&lt;span class="pp"&gt;Size::&lt;/span&gt;Absolute(&lt;span class="dv"&gt;16&lt;/span&gt;))&lt;/span&gt;
&lt;span id="cb1-9"&gt;&lt;a href="#cb1-9" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="op"&gt;.&lt;/span&gt;height(&lt;span class="pp"&gt;Size::&lt;/span&gt;Absolute(&lt;span class="dv"&gt;16&lt;/span&gt;))&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-10"&gt;&lt;a href="#cb1-10" aria-hidden="true"&gt;&lt;/a&gt;    &lt;/span&gt;
&lt;span id="cb1-11"&gt;&lt;a href="#cb1-11" aria-hidden="true"&gt;&lt;/a&gt;container&lt;span class="op"&gt;.&lt;/span&gt;place(&lt;/span&gt;
&lt;span id="cb1-12"&gt;&lt;a href="#cb1-12" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="op"&gt;&amp;amp;&lt;/span&gt;&lt;span class="kw"&gt;mut&lt;/span&gt; padding_box&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-13"&gt;&lt;a href="#cb1-13" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="pp"&gt;HorAlign::&lt;/span&gt;Right&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-14"&gt;&lt;a href="#cb1-14" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="pp"&gt;VertAlign::&lt;/span&gt;Center&lt;/span&gt;
&lt;span id="cb1-15"&gt;&lt;a href="#cb1-15" aria-hidden="true"&gt;&lt;/a&gt;)&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;The result (brush preview on the bottom right):&lt;/p&gt;
&lt;figure&gt;
&lt;video src="https://u.peppe.rs/OtU.mp4" controls=""&gt;&lt;a href="https://u.peppe.rs/OtU.mp4"&gt;Day 17&lt;/a&gt;&lt;/video&gt;&lt;figcaption aria-hidden="true"&gt;Day 17&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-16"&gt;Day 16&lt;/h3&gt;
&lt;p&gt;The embedded lisp is coming along nicely, users can load a custom &lt;code&gt;rc.lisp&lt;/code&gt;, which is evaluated on startup. To disable to grid on start, for example:&lt;/p&gt;
&lt;div class="sourceCode" id="cb2"&gt;&lt;pre class="sourceCode scheme"&gt;&lt;code class="sourceCode scheme"&gt;&lt;span id="cb2-1"&gt;&lt;a href="#cb2-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;;;; rc.lisp&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-2"&gt;&lt;a href="#cb2-2" aria-hidden="true"&gt;&lt;/a&gt;(toggle-grid)&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Some aliases to switch between brushes:&lt;/p&gt;
&lt;div class="sourceCode" id="cb3"&gt;&lt;pre class="sourceCode scheme"&gt;&lt;code class="sourceCode scheme"&gt;&lt;span id="cb3-1"&gt;&lt;a href="#cb3-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;;;; rc.lisp&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb3-2"&gt;&lt;a href="#cb3-2" aria-hidden="true"&gt;&lt;/a&gt;(&lt;span class="ex"&gt;define&lt;/span&gt;&lt;span class="fu"&gt; &lt;/span&gt;(brush kind)&lt;/span&gt;
&lt;span id="cb3-3"&gt;&lt;a href="#cb3-3" aria-hidden="true"&gt;&lt;/a&gt;  (&lt;span class="kw"&gt;cond&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb3-4"&gt;&lt;a href="#cb3-4" aria-hidden="true"&gt;&lt;/a&gt;    ((&lt;span class="kw"&gt;eq?&lt;/span&gt; kind &amp;#39;f) (brush-fill))&lt;/span&gt;
&lt;span id="cb3-5"&gt;&lt;a href="#cb3-5" aria-hidden="true"&gt;&lt;/a&gt;    ((&lt;span class="kw"&gt;eq?&lt;/span&gt; kind &amp;#39;c) (brush-circle))&lt;/span&gt;
&lt;span id="cb3-6"&gt;&lt;a href="#cb3-6" aria-hidden="true"&gt;&lt;/a&gt;    ((&lt;span class="kw"&gt;eq?&lt;/span&gt; kind &amp;#39;l) (brush-line))&lt;/span&gt;
&lt;span id="cb3-7"&gt;&lt;a href="#cb3-7" aria-hidden="true"&gt;&lt;/a&gt;    ((&lt;span class="kw"&gt;eq?&lt;/span&gt; kind &amp;#39;l+) (brush-line-extend))&lt;/span&gt;
&lt;span id="cb3-8"&gt;&lt;a href="#cb3-8" aria-hidden="true"&gt;&lt;/a&gt;    (&lt;span class="kw"&gt;else&lt;/span&gt; (brush-circle))))&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;The following script draws a straight line along a given axis, at a given distance from the canvas boundary:&lt;/p&gt;
&lt;figure&gt;
&lt;video src="https://u.peppe.rs/b3i.mp4" controls=""&gt;&lt;a href="https://u.peppe.rs/b3i.mp4"&gt;Day 16&lt;/a&gt;&lt;/video&gt;&lt;figcaption aria-hidden="true"&gt;Day 16&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-15"&gt;Day 15&lt;/h3&gt;
&lt;p&gt;I began writing a standard library for the lisp, in lisp. It includes basic list operations: &lt;code&gt;car&lt;/code&gt;, &lt;code&gt;cdr&lt;/code&gt;, &lt;code&gt;null?&lt;/code&gt;, &lt;code&gt;list&lt;/code&gt;, higher order functions: &lt;code&gt;map&lt;/code&gt;, &lt;code&gt;filter&lt;/code&gt;, &lt;code&gt;fold&lt;/code&gt;:&lt;/p&gt;
&lt;div class="sourceCode" id="cb4"&gt;&lt;pre class="sourceCode lisp"&gt;&lt;code class="sourceCode commonlisp"&gt;&lt;span id="cb4-1"&gt;&lt;a href="#cb4-1" aria-hidden="true"&gt;&lt;/a&gt;(define (member? item ls)&lt;/span&gt;
&lt;span id="cb4-2"&gt;&lt;a href="#cb4-2" aria-hidden="true"&gt;&lt;/a&gt;  (fold &lt;span class="dv"&gt;#f&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb4-3"&gt;&lt;a href="#cb4-3" aria-hidden="true"&gt;&lt;/a&gt;        (&lt;span class="kw"&gt;lambda&lt;/span&gt; (acc x) (&lt;span class="kw"&gt;or&lt;/span&gt; acc (eq? item x)))&lt;/span&gt;
&lt;span id="cb4-4"&gt;&lt;a href="#cb4-4" aria-hidden="true"&gt;&lt;/a&gt;        ls))&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;h3 id="day-14"&gt;Day 14&lt;/h3&gt;
&lt;p&gt;I attempted a &lt;a href="https://peppe.rs/art/ramen_noodles.png"&gt;small art piece&lt;/a&gt; using the editor, while it was largely usable, I felt a certain lack of feedback. The brushes just didn’t relay as much info as I’d have liked, for example, the approximate points of the line or the angle made by the line against the x-axis. Unfortunately, the existing infrastructure around brushes and line drawing didn’t easily allow for this either. I went ahead and reimplemented brushes, and added a new flood fill brush too:&lt;/p&gt;
&lt;figure&gt;
&lt;video src="https://u.peppe.rs/8q.mp4" controls=""&gt;&lt;a href="https://u.peppe.rs/8q.mp4"&gt;Day 14&lt;/a&gt;&lt;/video&gt;&lt;figcaption aria-hidden="true"&gt;Day 14&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-13"&gt;Day 13&lt;/h3&gt;
&lt;p&gt;I added a few more forms to the &lt;code&gt;lisp&lt;/code&gt; evaluator. It handles recursion, definitions, variable mutation and more. The prelude contains 20 subroutines so far, including comparision and logic operators. The REPL interface on the SDL side requires some UX tweaks; environment based completion, readline motions sound doable.&lt;/p&gt;
&lt;figure&gt;
&lt;video src="https://u.peppe.rs/u3.mp4" controls=""&gt;&lt;a href="https://u.peppe.rs/u3.mp4"&gt;Day 13&lt;/a&gt;&lt;/video&gt;&lt;figcaption aria-hidden="true"&gt;Day 13&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-12"&gt;Day 12&lt;/h3&gt;
&lt;p&gt;I lifted most of &lt;a href="https://github.com/murarth/ketos"&gt;murarth/ketos&lt;/a&gt; into the editor. &lt;code&gt;ketos&lt;/code&gt;’s implementation of &lt;code&gt;lisp&lt;/code&gt; is too vast for my use case. For example, the editor does not need data types to handle raw strings or byte strings. I have got a basic evaluator running inside the SDL2 context (notice the &lt;code&gt;lisp&lt;/code&gt; REPL at the bottom of the window). Over the following days, I intend to create a set of prelude functions to manipulate the pixmap. Users can implement their own brushes, dithering patterns, keybinds and more (hopefully).&lt;/p&gt;
&lt;figure&gt;
&lt;video src="https://u.peppe.rs/y0.mp4" controls=""&gt;&lt;a href="https://u.peppe.rs/y0.mp4"&gt;Day 12&lt;/a&gt;&lt;/video&gt;&lt;figcaption aria-hidden="true"&gt;Day 12&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-11"&gt;Day 11&lt;/h3&gt;
&lt;p&gt;I intend to supplement the editor with scripting language and an inbuilt REPL for the same. I began by implementing a text box widget from scratch, with history and readline like editing:&lt;/p&gt;
&lt;figure&gt;
&lt;video src="https://u.peppe.rs/Mh.mp4" controls=""&gt;&lt;a href="https://u.peppe.rs/Mh.mp4"&gt;Day 11&lt;/a&gt;&lt;/video&gt;&lt;figcaption aria-hidden="true"&gt;Day 11&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-10"&gt;Day 10&lt;/h3&gt;
&lt;p&gt;I started reading up on dithering methods and half-toning, I wanted to create a dithering brush that would automatically produce popular dithering patterns. The method that caught my eye (and also the one used most often in pixel art), was Bayer’s ordered dithering. When applied to a black and white image, each pixel, based on its intensity, is mapped to a 4x4 grid of pixels. A completely empty (completely black) 4x4 grid represents zero intensity, and a filled 4x4 grid represents full intensity. Bayer’s ordered dithering can produce 15 steps of intensity between zero and full (by switching on exactly 1 pixel more at each level), thus, being able to draw 17 “shades” from white to black. Creating a dithering brush from here was fairly trivial. Our pixmap is supposed to represent the final dithered image, it must be divided into 4x4 grids. Each grid is colored based on the intensity of the brush passing over it:&lt;/p&gt;
&lt;figure&gt;
&lt;img src="https://u.peppe.rs/Mn.png" alt="Day 10" /&gt;&lt;figcaption aria-hidden="true"&gt;Day 10&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-9"&gt;Day 9&lt;/h3&gt;
&lt;p&gt;I started working towards an interface. I like the idea of a largely read-only HUD, i. e., an interface that simply describes the state of the application. Changes to this state are initiated via keybinds or text commands. I am proud of the symmetry indicator; &lt;code&gt;-&lt;/code&gt; for horizontal symmetry, &lt;code&gt;|&lt;/code&gt; for vertical symmetry, &lt;code&gt;+&lt;/code&gt; for radial symmetry.&lt;/p&gt;
&lt;figure&gt;
&lt;img src="https://u.peppe.rs/hx.png" alt="Day 9" /&gt;&lt;figcaption aria-hidden="true"&gt;Day 9&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-8"&gt;Day 8&lt;/h3&gt;
&lt;p&gt;One of my favourite features of GIMP was symmetric editing. I added some coordinate geometry primitives to my pixmap abstraction, allowing for mirroring and reflecting figures about lines or points. The result was an ergonomic function that applies symmetry to any painting operation, (undo/redo works as expected):&lt;/p&gt;
&lt;div class="sourceCode" id="cb5"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb5-1"&gt;&lt;a href="#cb5-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;let&lt;/span&gt; line &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;self&lt;/span&gt;&lt;span class="op"&gt;.&lt;/span&gt;pixmap&lt;span class="op"&gt;.&lt;/span&gt;get_line(start&lt;span class="op"&gt;,&lt;/span&gt; end)&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb5-2"&gt;&lt;a href="#cb5-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;let&lt;/span&gt; sym_line &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;self&lt;/span&gt;&lt;span class="op"&gt;.&lt;/span&gt;symmetry&lt;span class="op"&gt;.&lt;/span&gt;apply(&lt;span class="op"&gt;&amp;amp;&lt;/span&gt;line)&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb5-3"&gt;&lt;a href="#cb5-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;for&lt;/span&gt; point on line&lt;span class="op"&gt;.&lt;/span&gt;extend(sym_line) &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb5-4"&gt;&lt;a href="#cb5-4" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="co"&gt;// draw to window&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb5-5"&gt;&lt;a href="#cb5-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;figure&gt;
&lt;video src="https://u.peppe.rs/B1.mp4" controls=""&gt;&lt;a href="https://u.peppe.rs/B1.mp4"&gt;Day 8&lt;/a&gt;&lt;/video&gt;&lt;figcaption aria-hidden="true"&gt;Day 8&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-7"&gt;Day 7&lt;/h3&gt;
&lt;p&gt;Bresenham saves the day again! This time, I implemented his line drawing algorithm, to, well, draw lines. Each point on the line is then “buffed” based on the active brush size. Today’s changes fit in very well with the undo system and the brush size feature. Creating the right abstractions, one at a time :)&lt;/p&gt;
&lt;figure&gt;
&lt;video src="https://u.peppe.rs/xt.mp4" controls=""&gt;&lt;a href="https://u.peppe.rs/xt.mp4"&gt;Day 7&lt;/a&gt;&lt;/video&gt;&lt;figcaption aria-hidden="true"&gt;Day 7&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-6"&gt;Day 6&lt;/h3&gt;
&lt;p&gt;I extended Bresenham’s algorithm to draw not just circle outlines, but also generate their fills. Unlike Bresenham’s algorithm, this variant generates points for two quadrants at once, these points are mirrored over the dividing axis to generate the other two quadrants.&lt;/p&gt;
&lt;figure&gt;
&lt;img src="https://u.peppe.rs/f3.png" alt="Day 6" /&gt;&lt;figcaption aria-hidden="true"&gt;Day 6&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-5"&gt;Day 5&lt;/h3&gt;
&lt;p&gt;I discovered and implemented Bresenham’s algorithm for efficient circle drawing. The algorithm allowed for sized circular brushes, something I really liked from GIMP. Very convenient that the Wikipedia page for Bresenham’s algorithm also includes a section about optimizing for integer based arithmetic. I managed to abstract out another giant component of the application, the pixmap. Any image is just a grid of pixels (a pixmap), where the pixel’s value is decided by the application (1-bit in my case). I could potentially extend the application to a 24-bit image editor!&lt;/p&gt;
&lt;figure&gt;
&lt;video src="https://u.peppe.rs/Kh.mp4" controls=""&gt;&lt;a href="https://u.peppe.rs/Kh.mp4"&gt;Day 5&lt;/a&gt;&lt;/video&gt;&lt;figcaption aria-hidden="true"&gt;Day 5&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-4"&gt;Day 4&lt;/h3&gt;
&lt;p&gt;I created a generic “undo stack” data structure that allows for infinite “undos” and “redos”. Every modification operation to the grid is persisted to the application state. A couple of keybinds allow the user to revert and re-apply these operations! I expect abstracting this component will come in handy down the line.&lt;/p&gt;
&lt;figure&gt;
&lt;video src="https://u.peppe.rs/w5.mp4" controls=""&gt;&lt;a href="https://u.peppe.rs/w5.mp4"&gt;Day 4&lt;/a&gt;&lt;/video&gt;&lt;figcaption aria-hidden="true"&gt;Day 4&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-3"&gt;Day 3&lt;/h3&gt;
&lt;p&gt;I implemented the bare minimum required to call the program an “editor”. The application displays a grid, tracks mouse events, paints white to the canvas on left click, and black to the canvas on right click. I created a make-shift MVC architecture à la Elm in Rust.&lt;/p&gt;
&lt;figure&gt;
&lt;video src="https://u.peppe.rs/GF.mp4" controls=""&gt;&lt;a href="https://u.peppe.rs/GF.mp4"&gt;Day 3&lt;/a&gt;&lt;/video&gt;&lt;figcaption aria-hidden="true"&gt;Day 3&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-2"&gt;Day 2&lt;/h3&gt;
&lt;p&gt;I started figuring out event handling today. Implemented a couple of keybinds to zoom in/out of the drawing area. Conversions of SDL2 coordinates (measured in signed 32 bit integers) to my internal “drawing area” coordinates (measured in unsigned 32 bit integers) is very annoying. Hopefully the unchecked conversions won’t haunt me later.&lt;/p&gt;
&lt;figure&gt;
&lt;video src="https://u.peppe.rs/L4.mp4" controls=""&gt;&lt;a href="https://u.peppe.rs/L4.mp4"&gt;Day 2&lt;/a&gt;&lt;/video&gt;&lt;figcaption aria-hidden="true"&gt;Day 2&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;h3 id="day-1"&gt;Day 1&lt;/h3&gt;
&lt;p&gt;Getting started with Rust and SDL2 is very straightforward. The &lt;code&gt;rust-sdl2&lt;/code&gt; library contains some detailed examples that allowed me to get all the way to drawing a grid from a &lt;code&gt;Vec&amp;lt;bool&amp;gt;&lt;/code&gt;:&lt;/p&gt;
&lt;figure&gt;
&lt;img src="https://u.peppe.rs/Ma.png" alt="Day 1" /&gt;&lt;figcaption aria-hidden="true"&gt;Day 1&lt;/figcaption&gt;
&lt;/figure&gt;</description>
<link>https://peppe.rs/posts/SDL2_devlog/</link>
<pubDate>Sun, 11 Apr 2021 10:46:00 +0000</pubDate>
<guid>https://peppe.rs/posts/SDL2_devlog/</guid>
</item>
<item>
<title>Self-hosting Git</title>
<description>&lt;p&gt;Earlier this week, I began migrating my repositories from Github to &lt;a href="https://git.zx2c4.com/cgit/about/"&gt;cgit&lt;/a&gt;. If you care at all about big corporates turning open-source into a T-shirt farming service, this is the way to go.&lt;/p&gt;
&lt;h3 id="offerings"&gt;Offerings&lt;/h3&gt;
&lt;p&gt;cgit is &lt;em&gt;very&lt;/em&gt; bare bones. It is &lt;a href="https://tools.ietf.org/html/rfc3875"&gt;cgi-based&lt;/a&gt; web interface to git, and nothing more. You may browse repositories, view diffs, commit logs and even clone via http. If you are looking to replace Github with cgit, keep in mind that cgit does not handle issues or pull/merge requests. If people wish to contribute to your work, they would have to send you a patch via email.&lt;/p&gt;
&lt;h3 id="setup"&gt;Setup&lt;/h3&gt;
&lt;p&gt;Installing cgit is fairly straightforward, if you would like to compile it from source:&lt;/p&gt;
&lt;div class="sourceCode" id="cb1"&gt;&lt;pre class="sourceCode sh"&gt;&lt;code class="sourceCode bash"&gt;&lt;span id="cb1-1"&gt;&lt;a href="#cb1-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;# fetch&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-2"&gt;&lt;a href="#cb1-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="fu"&gt;git&lt;/span&gt; clone https://git.zx2c4.com &lt;span class="kw"&gt;&amp;amp;&amp;amp;&lt;/span&gt; &lt;span class="bu"&gt;cd&lt;/span&gt; cgit&lt;/span&gt;
&lt;span id="cb1-3"&gt;&lt;a href="#cb1-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="fu"&gt;git&lt;/span&gt; submodule init&lt;/span&gt;
&lt;span id="cb1-4"&gt;&lt;a href="#cb1-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="fu"&gt;git&lt;/span&gt; submodule update&lt;/span&gt;
&lt;span id="cb1-5"&gt;&lt;a href="#cb1-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb1-6"&gt;&lt;a href="#cb1-6" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;# install&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-7"&gt;&lt;a href="#cb1-7" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="fu"&gt;make&lt;/span&gt; NO_LUA=1&lt;/span&gt;
&lt;span id="cb1-8"&gt;&lt;a href="#cb1-8" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="fu"&gt;sudo&lt;/span&gt; make install&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;This would drop the cgit cgi script (and the default css) into &lt;code&gt;/var/www/htdocs/cgit&lt;/code&gt;. You may configure cgit by editing &lt;code&gt;/etc/cgitrc&lt;/code&gt;. I specify the &lt;code&gt;NO_LUA&lt;/code&gt; flag to compile without lua support, exclude that flag if you would like to extend cgit via lua scripts.&lt;/p&gt;
&lt;h3 id="going-live"&gt;Going live&lt;/h3&gt;
&lt;p&gt;You might want to use, &lt;a href="https://github.com/gnosek/fcgiwrap"&gt;fcgiwrap&lt;/a&gt;, a &lt;a href="http://www.nongnu.org/fastcgi"&gt;fastcgi&lt;/a&gt; wrapper for &lt;code&gt;cgi&lt;/code&gt; scripts,&lt;/p&gt;
&lt;div class="sourceCode" id="cb2"&gt;&lt;pre class="sourceCode sh"&gt;&lt;code class="sourceCode bash"&gt;&lt;span id="cb2-1"&gt;&lt;a href="#cb2-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="fu"&gt;sudo&lt;/span&gt; apt install fcgiwrap&lt;/span&gt;
&lt;span id="cb2-2"&gt;&lt;a href="#cb2-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="fu"&gt;sudo&lt;/span&gt; systemctl start fcgiwrap.socket&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Expose the cgit cgi script to the web via &lt;code&gt;nginx&lt;/code&gt;:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;# nginx.conf
server {
  listen 80;
  server_name git.example.com;

  # serve static files
  location ~* ^.+\.(css|png|ico)$ {
    root /var/www/htdocs/cgit;
  }

  location / {
    fastcgi_pass  unix:/run/fcgiwrap.socket;
    fastcgi_param SCRIPT_FILENAME /var/www/htdocs/cgit/cgit.cgi; # the default location of the cgit cgi script
    fastcgi_param PATH_INFO       $uri;
    fastcgi_param QUERY_STRING    $args;
  }
}&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Point cgit to your git repositories:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;# /etc/cgitrc
scan-path=/path/to/git/repos&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;&lt;strong&gt;&lt;em&gt;Note&lt;/em&gt;&lt;/strong&gt;: &lt;em&gt;&lt;code&gt;scan-path&lt;/code&gt; works best if you stick it at the end of your &lt;code&gt;cgitrc&lt;/code&gt;&lt;/em&gt;.&lt;/p&gt;
&lt;p&gt;You may now create remote repositories at &lt;code&gt;/path/to/git/repos&lt;/code&gt;, via:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;git init --bare&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Add the remote to your local repository:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;git remote set-url origin user@remote:/above/path
git push origin master&lt;/code&gt;&lt;/pre&gt;
&lt;h3 id="configuration"&gt;Configuration&lt;/h3&gt;
&lt;p&gt;cgit is fairly easy to configure, all configuration options can be found &lt;a href="https://git.zx2c4.com/cgit/tree/cgitrc.5.txt"&gt;in the manual&lt;/a&gt;, here are a couple of cool ones though:&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;enable-commit-graph&lt;/strong&gt;: Generates a text based graphical representation of the commit history, similar to &lt;code&gt;git log --graph --oneline&lt;/code&gt;.&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;| * |    Add support for configuration file
* | |    simplify command parsing logic
* | |    Refactor parsers
* | |    Add basic tests
* | |    Merge remote-tracking branch &amp;#39;origin/master&amp;#39; in...
|\| |
| * |    add installation instructions for nix
| * |    switch to pancurses backendv0.2.2
| * |    bump to v0.2.2
* | |    Merge branch &amp;#39;master&amp;#39; into feature/larger-names...
|\| |
| * |    enable feature based compilation to support win...
| * |    remove dependency on rustc v1.45, bump to v0.2....
| * |      Merge branch &amp;#39;feature/windows&amp;#39; of https://git...
| |\ \
| | * |    add windows to github actions
| | * |    switch to crossterm backend
| | * |      Merge branch &amp;#39;fix/duplicate-habits&amp;#39;
| | |\ \
| | | * |    move duplicate check to command parsing blo...&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;&lt;strong&gt;section-from-path&lt;/strong&gt;: This option paired with &lt;code&gt;scan-path&lt;/code&gt; will automatically generate sections in your cgit index page, from the path to each repo. For example, the directory structure used to generate sections on &lt;a href="https://git.peppe.rs"&gt;my cgit instance&lt;/a&gt; looks like this:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;├── cli
│   ├── dijo
│   ├── eva
│   ├── pista
│   ├── taizen
│   └── xcursorlocate
├── config
│   ├── dotfiles
│   └── nixos
├── fonts
│   ├── curie
│   └── scientifica
├── languages
│   └── lisk
├── libs
│   ├── cutlass
│   └── fondant
├── terminfo
├── university
│   └── furby
└── web
    └── isostatic&lt;/code&gt;&lt;/pre&gt;
&lt;h3 id="ease-of-use"&gt;Ease of use&lt;/h3&gt;
&lt;p&gt;As I mentioned before, &lt;code&gt;cgit&lt;/code&gt; is simply a view into your git repositories, you will have to manually create new repositories by entering your remote and using &lt;code&gt;git init --bare&lt;/code&gt;. Here are a couple of scripts I wrote to perform actions on remotes, think of it as a smaller version of Github’s &lt;code&gt;gh&lt;/code&gt; program.&lt;/p&gt;
&lt;p&gt;You may save these scripts as &lt;code&gt;git-script-name&lt;/code&gt; and drop them in your &lt;code&gt;$PATH&lt;/code&gt;, and git will automatically add an alias called &lt;code&gt;script-name&lt;/code&gt;, callable via:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;git script-name&lt;/code&gt;&lt;/pre&gt;
&lt;h4 id="git-new-repo"&gt;git-new-repo&lt;/h4&gt;
&lt;p&gt;Creates a new repository on your remote, the first arg may be a path (section/repo-name) or just the repo name:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;#! /usr/bin/env bash
#
# usage:
# git new-repo section/repo-name
# 
# example:
# git new-repo fonts/scientifica
# creates: user@remote:fonts/scientifica

if [ $# -eq 0 ]; then
    echo &amp;quot;requires an arg&amp;quot;
    exit 1
fi

ssh user@remote git init --bare &amp;quot;$1&amp;quot;;&lt;/code&gt;&lt;/pre&gt;
&lt;h4 id="git-set-desc"&gt;git-set-desc&lt;/h4&gt;
&lt;p&gt;To set a one line repository description. It simply copies the local &lt;code&gt;.git/description&lt;/code&gt;, into &lt;code&gt;remote/description&lt;/code&gt;. &lt;code&gt;cgit&lt;/code&gt; displays the contents of this file on the index page:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;#! /usr/bin/env bash
#
# usage:
# enter repo description into .git/description and run:
# git set-desc 

remote=$(git remote get-url --push origin)
scp .git/description &amp;quot;$remote/description&amp;quot;&lt;/code&gt;&lt;/pre&gt;</description>
<link>https://peppe.rs/posts/self-hosting_git/</link>
<pubDate>Sat, 17 Oct 2020 07:04:00 +0000</pubDate>
<guid>https://peppe.rs/posts/self-hosting_git/</guid>
</item>
<item>
<title>NixOS</title>
<description>&lt;p&gt;I have been eyeing operating systems with functional package managers for a while now, aka, NixOS or Guix. Reproducible builds, declarative and rollback-able system configuration, system consistency, all sound pretty cool. I have been using NixOS for about a month now.&lt;/p&gt;
&lt;h3 id="installation"&gt;Installation&lt;/h3&gt;
&lt;p&gt;I went with their minimal installation ISO. The installation was pretty smooth from start to end, no hitches there. The entire &lt;a href="https://nixos.org/manual/nixos/stable/"&gt;manual&lt;/a&gt; is available offline, and is accessible during the installation. Very handy.&lt;/p&gt;
&lt;h3 id="setup"&gt;Setup&lt;/h3&gt;
&lt;p&gt;The entire system is configured via &lt;code&gt;/etc/nixos/configuration.nix&lt;/code&gt;. Wifi, &lt;code&gt;libinput&lt;/code&gt; gestures, audio, locale settings, there are options for literally everything. You can declaratively write down the packages you want installed too. With fresh installs of most distros, I usually fumble with getting things like screen backlight and media keys to work. If I do manage to fix it, I can’t carry it forward to future installations trivially. Getting all my hardware to work on NixOS is as easy as:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;{
    server.xserver.libinput.enable = true;  # touchpad
    programs.light.enable = true;           # backlight
    hardware.pulseaudio.enable = true;      # audio
    networking.wireless.enable = true;      # wifi
}&lt;/code&gt;&lt;/pre&gt;
&lt;h3 id="developing-with-nix"&gt;Developing with Nix&lt;/h3&gt;
&lt;p&gt;Nix makes it easy to enter environments that aren’t affected by your system configuration using &lt;code&gt;nix-shell&lt;/code&gt;.&lt;/p&gt;
&lt;p&gt;Builds may be generated by specifying a &lt;code&gt;default.nix&lt;/code&gt; file, and running &lt;code&gt;nix-build&lt;/code&gt;. Conventional package managers require you to specify a dependency list, but there is no guarantee that this list is complete. The package will build on your machine even if you forget a dependency. However, with Nix, packages are installed to &lt;code&gt;/nix/store&lt;/code&gt;, and not global paths such as &lt;code&gt;/usr/bin/...&lt;/code&gt;, if your project builds, it means you have included every last one.&lt;/p&gt;
&lt;p&gt;Issues on most my projects have been “unable to build because &lt;code&gt;libxcb&lt;/code&gt; is missing”, or “this version of &lt;code&gt;openssl&lt;/code&gt; is too old”. Tools like &lt;code&gt;cargo&lt;/code&gt; and &lt;code&gt;pip&lt;/code&gt; are poor package managers. While they &lt;em&gt;can&lt;/em&gt; guarantee that Rust or Python dependencies are met, they make assumptions about the target system.&lt;/p&gt;
&lt;p&gt;For example, &lt;a href="https://github.com/nerdypepper/site"&gt;this website&lt;/a&gt; is now built using Nix, anyone using Nix may simply, clone the repository and run &lt;code&gt;./generate.sh&lt;/code&gt;, and it would &lt;em&gt;just work&lt;/em&gt;, while keeping your global namespace clean™:&lt;/p&gt;
&lt;div class="sourceCode" id="cb2"&gt;&lt;pre class="sourceCode bash"&gt;&lt;code class="sourceCode bash"&gt;&lt;span id="cb2-1"&gt;&lt;a href="#cb2-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;#! /usr/bin/env nix-shell&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-2"&gt;&lt;a href="#cb2-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;#! nix-shell -i bash -p eva pandoc esh&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-3"&gt;&lt;a href="#cb2-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb2-4"&gt;&lt;a href="#cb2-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;# some bash magic ;)&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Dependencies are included with the &lt;code&gt;-p&lt;/code&gt; flag, the shell script is executed with an interpreter, specified with the &lt;code&gt;-i&lt;/code&gt; flag.&lt;/p&gt;
&lt;h3 id="impressions"&gt;Impressions&lt;/h3&gt;
&lt;p&gt;NixOS is by no means, simple. As a newcomer, using Nix was not easy, heck, I had to learn a purely functional, lazy language to just build programs. There is a lot to be desired on the tooling front as well. A well fleshed out LSP plugin would be nice (&lt;a href="https://github.com/nix-community/rnix-lsp"&gt;rnix-lsp looks promising&lt;/a&gt;).&lt;/p&gt;
&lt;p&gt;Being able to rollback changes at a system level is cool. Package broke something? Just &lt;code&gt;nixos-rebuild switch --rollback&lt;/code&gt;! Deleted &lt;code&gt;nix&lt;/code&gt; by mistake? Find the binary in &lt;code&gt;/nix/store&lt;/code&gt; and rollback! You aren’t punished for not thinking twice.&lt;/p&gt;
&lt;p&gt;I don’t see myself switching to anything else in the near future, NixOS does a lot of things right. If I ever need to reinstall NixOS, I can generate an &lt;a href="https://github.com/nix-community/nixos-generators"&gt;image of my current system&lt;/a&gt;.&lt;/p&gt;
&lt;p&gt;&lt;a href="https://u.peppe.rs/6m.png"&gt;&lt;img src="https://u.peppe.rs/6m.png" /&gt;&lt;/a&gt;&lt;/p&gt;</description>
<link>https://peppe.rs/posts/nixOS/</link>
<pubDate>Tue, 01 Sep 2020 07:08:00 +0000</pubDate>
<guid>https://peppe.rs/posts/nixOS/</guid>
</item>
<item>
<title>Gripes With Go</title>
<description>&lt;p&gt;You’ve read a lot of posts about the shortcomings of the Go programming language, so what’s one more.&lt;/p&gt;
&lt;ol type="1"&gt;
&lt;li&gt;&lt;a href="#lack-of-sum-types"&gt;Lack of sum types&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href="#type-assertions"&gt;Type assertions&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href="#date-and-time"&gt;Date and Time&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href="#statements-over-expressions"&gt;Statements over Expressions&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href="#erroring-out-on-unused-variables"&gt;Erroring out on unused variables&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href="#error-handling"&gt;Error handling&lt;/a&gt;&lt;/li&gt;
&lt;/ol&gt;
&lt;h3 id="lack-of-sum-types"&gt;Lack of Sum types&lt;/h3&gt;
&lt;p&gt;A “Sum” type is a data type that can hold one of many states at a given time, similar to how a boolean can hold a true or a false, not too different from an &lt;code&gt;enum&lt;/code&gt; type in C. Go lacks &lt;code&gt;enum&lt;/code&gt; types unfortunately, and you are forced to resort to crafting your own substitute.&lt;/p&gt;
&lt;p&gt;A type to represent gender for example:&lt;/p&gt;
&lt;div class="sourceCode" id="cb1"&gt;&lt;pre class="sourceCode go"&gt;&lt;code class="sourceCode go"&gt;&lt;span id="cb1-1"&gt;&lt;a href="#cb1-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; Gender &lt;span class="dt"&gt;int&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-2"&gt;&lt;a href="#cb1-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb1-3"&gt;&lt;a href="#cb1-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;const&lt;/span&gt; (&lt;/span&gt;
&lt;span id="cb1-4"&gt;&lt;a href="#cb1-4" aria-hidden="true"&gt;&lt;/a&gt;    Male Gender = &lt;span class="ot"&gt;iota&lt;/span&gt;  &lt;span class="co"&gt;// assigns Male to 0&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-5"&gt;&lt;a href="#cb1-5" aria-hidden="true"&gt;&lt;/a&gt;    Female              &lt;span class="co"&gt;// assigns Female to 1&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-6"&gt;&lt;a href="#cb1-6" aria-hidden="true"&gt;&lt;/a&gt;    Other               &lt;span class="co"&gt;// assigns Other to 2&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-7"&gt;&lt;a href="#cb1-7" aria-hidden="true"&gt;&lt;/a&gt;)&lt;/span&gt;
&lt;span id="cb1-8"&gt;&lt;a href="#cb1-8" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb1-9"&gt;&lt;a href="#cb1-9" aria-hidden="true"&gt;&lt;/a&gt;fmt.Println(&lt;span class="st"&gt;&amp;quot;My gender is &amp;quot;&lt;/span&gt;, Male)&lt;/span&gt;
&lt;span id="cb1-10"&gt;&lt;a href="#cb1-10" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// My gender is 0&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-11"&gt;&lt;a href="#cb1-11" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// Oops! We have to implement String() for Gender ...&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-12"&gt;&lt;a href="#cb1-12" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb1-13"&gt;&lt;a href="#cb1-13" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;func&lt;/span&gt; (g Gender) String() &lt;span class="dt"&gt;string&lt;/span&gt; {&lt;/span&gt;
&lt;span id="cb1-14"&gt;&lt;a href="#cb1-14" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;switch&lt;/span&gt; (g) {&lt;/span&gt;
&lt;span id="cb1-15"&gt;&lt;a href="#cb1-15" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;case&lt;/span&gt; &lt;span class="dv"&gt;0&lt;/span&gt;: &lt;span class="kw"&gt;return&lt;/span&gt; &lt;span class="st"&gt;&amp;quot;Male&amp;quot;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-16"&gt;&lt;a href="#cb1-16" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;case&lt;/span&gt; &lt;span class="dv"&gt;1&lt;/span&gt;: &lt;span class="kw"&gt;return&lt;/span&gt; &lt;span class="st"&gt;&amp;quot;Female&amp;quot;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-17"&gt;&lt;a href="#cb1-17" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;default&lt;/span&gt;: &lt;span class="kw"&gt;return&lt;/span&gt; &lt;span class="st"&gt;&amp;quot;Other&amp;quot;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-18"&gt;&lt;a href="#cb1-18" aria-hidden="true"&gt;&lt;/a&gt;    }&lt;/span&gt;
&lt;span id="cb1-19"&gt;&lt;a href="#cb1-19" aria-hidden="true"&gt;&lt;/a&gt;}&lt;/span&gt;
&lt;span id="cb1-20"&gt;&lt;a href="#cb1-20" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb1-21"&gt;&lt;a href="#cb1-21" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// You can accidentally do stupid stuff like:&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-22"&gt;&lt;a href="#cb1-22" aria-hidden="true"&gt;&lt;/a&gt;gender := Male + &lt;span class="dv"&gt;1&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;The Haskell equivalent of the same:&lt;/p&gt;
&lt;div class="sourceCode" id="cb2"&gt;&lt;pre class="sourceCode haskell"&gt;&lt;code class="sourceCode haskell"&gt;&lt;span id="cb2-1"&gt;&lt;a href="#cb2-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;data&lt;/span&gt; &lt;span class="dt"&gt;Gender&lt;/span&gt; &lt;span class="ot"&gt;=&lt;/span&gt; &lt;span class="dt"&gt;Male&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-2"&gt;&lt;a href="#cb2-2" aria-hidden="true"&gt;&lt;/a&gt;            &lt;span class="op"&gt;|&lt;/span&gt; &lt;span class="dt"&gt;Female&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-3"&gt;&lt;a href="#cb2-3" aria-hidden="true"&gt;&lt;/a&gt;            &lt;span class="op"&gt;|&lt;/span&gt; &lt;span class="dt"&gt;Other&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-4"&gt;&lt;a href="#cb2-4" aria-hidden="true"&gt;&lt;/a&gt;            &lt;span class="kw"&gt;deriving&lt;/span&gt; (&lt;span class="dt"&gt;Show&lt;/span&gt;)&lt;/span&gt;
&lt;span id="cb2-5"&gt;&lt;a href="#cb2-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb2-6"&gt;&lt;a href="#cb2-6" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="fu"&gt;print&lt;/span&gt; &lt;span class="op"&gt;$&lt;/span&gt; &lt;span class="st"&gt;&amp;quot;My gender is &amp;quot;&lt;/span&gt; &lt;span class="op"&gt;++&lt;/span&gt; (&lt;span class="fu"&gt;show&lt;/span&gt; &lt;span class="dt"&gt;Male&lt;/span&gt;)&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;h3 id="type-assertions"&gt;Type Assertions&lt;/h3&gt;
&lt;p&gt;A downcast with an optional error check? What could go wrong?&lt;/p&gt;
&lt;p&gt;Type assertions in Go allow you to do:&lt;/p&gt;
&lt;div class="sourceCode" id="cb3"&gt;&lt;pre class="sourceCode go"&gt;&lt;code class="sourceCode go"&gt;&lt;span id="cb3-1"&gt;&lt;a href="#cb3-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;var&lt;/span&gt; x &lt;span class="kw"&gt;interface&lt;/span&gt;{} = &lt;span class="dv"&gt;7&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb3-2"&gt;&lt;a href="#cb3-2" aria-hidden="true"&gt;&lt;/a&gt;y, goodToGo := x.(&lt;span class="dt"&gt;int&lt;/span&gt;)&lt;/span&gt;
&lt;span id="cb3-3"&gt;&lt;a href="#cb3-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;if&lt;/span&gt; goodToGo {&lt;/span&gt;
&lt;span id="cb3-4"&gt;&lt;a href="#cb3-4" aria-hidden="true"&gt;&lt;/a&gt;    fmt.Println(y)&lt;/span&gt;
&lt;span id="cb3-5"&gt;&lt;a href="#cb3-5" aria-hidden="true"&gt;&lt;/a&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;The error check however is optional:&lt;/p&gt;
&lt;div class="sourceCode" id="cb4"&gt;&lt;pre class="sourceCode go"&gt;&lt;code class="sourceCode go"&gt;&lt;span id="cb4-1"&gt;&lt;a href="#cb4-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;var&lt;/span&gt; x &lt;span class="kw"&gt;interface&lt;/span&gt;{} = &lt;span class="dv"&gt;7&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb4-2"&gt;&lt;a href="#cb4-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;var&lt;/span&gt; y := x.(&lt;span class="dt"&gt;float64&lt;/span&gt;)&lt;/span&gt;
&lt;span id="cb4-3"&gt;&lt;a href="#cb4-3" aria-hidden="true"&gt;&lt;/a&gt;fmt.Println(y)&lt;/span&gt;
&lt;span id="cb4-4"&gt;&lt;a href="#cb4-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// results in a runtime error:&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb4-5"&gt;&lt;a href="#cb4-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// panic: interface conversion: interface {} is int, not float64&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;h3 id="date-and-time"&gt;Date and Time&lt;/h3&gt;
&lt;p&gt;Anyone that has written Go previously, will probably already know what I am getting at here. For the uninitiated, parsing and formatting dates in Go requires a “layout”. This “layout” is based on magical reference date:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;Mon Jan 2 15:04:05 MST 2006&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Which is the date produced when you write the first seven natural numbers like so:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;01/02 03:04:05 &amp;#39;06 -0700&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Parsing a string in &lt;code&gt;YYYY-MM-DD&lt;/code&gt; format would look something like:&lt;/p&gt;
&lt;div class="sourceCode" id="cb7"&gt;&lt;pre class="sourceCode go"&gt;&lt;code class="sourceCode go"&gt;&lt;span id="cb7-1"&gt;&lt;a href="#cb7-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;const&lt;/span&gt; layout = &lt;span class="st"&gt;&amp;quot;2006-01-02&amp;quot;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb7-2"&gt;&lt;a href="#cb7-2" aria-hidden="true"&gt;&lt;/a&gt;time.Parse(layout, &lt;span class="st"&gt;&amp;quot;2020-08-01&amp;quot;&lt;/span&gt;)&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;This so-called “intuitive” method of formatting dates doesn’t allow you to print &lt;code&gt;0000 hrs&lt;/code&gt; as &lt;code&gt;2400 hrs&lt;/code&gt;, it doesn’t allow you to omit the leading zero in 24 hour formats. It is rife with inconveniences, if only there were a &lt;a href="https://man7.org/linux/man-pages/man3/strftime.3.html"&gt;tried and tested&lt;/a&gt; date formatting convention …&lt;/p&gt;
&lt;h3 id="statements-over-expressions"&gt;Statements over Expressions&lt;/h3&gt;
&lt;p&gt;Statements have side effects, expressions return values. More often than not, expressions are easier to understand at a glance: evaluate the LHS and assign the same to the RHS.&lt;/p&gt;
&lt;p&gt;Rust allows you to create local namespaces, and treats blocks (&lt;code&gt;{}&lt;/code&gt;) as expressions:&lt;/p&gt;
&lt;div class="sourceCode" id="cb8"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb8-1"&gt;&lt;a href="#cb8-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;let&lt;/span&gt; twenty_seven &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb8-2"&gt;&lt;a href="#cb8-2" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;let&lt;/span&gt; three &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="dv"&gt;1&lt;/span&gt; &lt;span class="op"&gt;+&lt;/span&gt; &lt;span class="dv"&gt;2&lt;/span&gt;&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb8-3"&gt;&lt;a href="#cb8-3" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;let&lt;/span&gt; nine &lt;span class="op"&gt;=&lt;/span&gt; three &lt;span class="op"&gt;*&lt;/span&gt; three&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb8-4"&gt;&lt;a href="#cb8-4" aria-hidden="true"&gt;&lt;/a&gt;    nine &lt;span class="op"&gt;*&lt;/span&gt; three&lt;/span&gt;
&lt;span id="cb8-5"&gt;&lt;a href="#cb8-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;};&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;The Go equivalent of the same:&lt;/p&gt;
&lt;div class="sourceCode" id="cb9"&gt;&lt;pre class="sourceCode go"&gt;&lt;code class="sourceCode go"&gt;&lt;span id="cb9-1"&gt;&lt;a href="#cb9-1" aria-hidden="true"&gt;&lt;/a&gt;twenty_seven := &lt;span class="ot"&gt;nil&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb9-2"&gt;&lt;a href="#cb9-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb9-3"&gt;&lt;a href="#cb9-3" aria-hidden="true"&gt;&lt;/a&gt;three := &lt;span class="dv"&gt;1&lt;/span&gt; + &lt;span class="dv"&gt;2&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb9-4"&gt;&lt;a href="#cb9-4" aria-hidden="true"&gt;&lt;/a&gt;nine := three * three&lt;/span&gt;
&lt;span id="cb9-5"&gt;&lt;a href="#cb9-5" aria-hidden="true"&gt;&lt;/a&gt;twenty_seven = nine * three&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;h3 id="erroring-out-on-unused-variables"&gt;Erroring out on unused variables&lt;/h3&gt;
&lt;p&gt;Want to quickly prototype something? Go says no! In all seriousness, a warning would suffice, I don’t want to have to go back and comment each unused import out, only to come back and uncomment them a few seconds later.&lt;/p&gt;
&lt;h3 id="error-handling"&gt;Error handling&lt;/h3&gt;
&lt;div class="sourceCode" id="cb10"&gt;&lt;pre class="sourceCode go"&gt;&lt;code class="sourceCode go"&gt;&lt;span id="cb10-1"&gt;&lt;a href="#cb10-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;if&lt;/span&gt; err != &lt;span class="ot"&gt;nil&lt;/span&gt; { ... }&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Need I say more? I will, for good measure:&lt;/p&gt;
&lt;ol type="1"&gt;
&lt;li&gt;Error handling is optional&lt;/li&gt;
&lt;li&gt;Errors are propagated via a clunky &lt;code&gt;if&lt;/code&gt; + &lt;code&gt;return&lt;/code&gt; statement&lt;/li&gt;
&lt;/ol&gt;
&lt;p&gt;I prefer Haskell’s “Monadic” error handling, which is employed by Rust as well:&lt;/p&gt;
&lt;div class="sourceCode" id="cb11"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb11-1"&gt;&lt;a href="#cb11-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// 1. error handling is compulsory&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb11-2"&gt;&lt;a href="#cb11-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// 2. errors are propagated with the `?` operator&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb11-3"&gt;&lt;a href="#cb11-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; foo() &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;Result&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;&lt;span class="dt"&gt;String&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; &lt;span class="pp"&gt;io::&lt;/span&gt;&lt;span class="bu"&gt;Error&lt;/span&gt;&lt;span class="op"&gt;&amp;gt;&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb11-4"&gt;&lt;a href="#cb11-4" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;let&lt;/span&gt; &lt;span class="kw"&gt;mut&lt;/span&gt; f &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="pp"&gt;File::&lt;/span&gt;open(&lt;span class="st"&gt;&amp;quot;foo.txt&amp;quot;&lt;/span&gt;)&lt;span class="op"&gt;?;&lt;/span&gt; &lt;span class="co"&gt;// return if error&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb11-5"&gt;&lt;a href="#cb11-5" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;let&lt;/span&gt; &lt;span class="kw"&gt;mut&lt;/span&gt; s &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="dt"&gt;String&lt;/span&gt;&lt;span class="pp"&gt;::&lt;/span&gt;new()&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb11-6"&gt;&lt;a href="#cb11-6" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb11-7"&gt;&lt;a href="#cb11-7" aria-hidden="true"&gt;&lt;/a&gt;    f&lt;span class="op"&gt;.&lt;/span&gt;read_to_string(&lt;span class="op"&gt;&amp;amp;&lt;/span&gt;&lt;span class="kw"&gt;mut&lt;/span&gt; s)&lt;span class="op"&gt;?;&lt;/span&gt; &lt;span class="co"&gt;// return if error&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb11-8"&gt;&lt;a href="#cb11-8" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb11-9"&gt;&lt;a href="#cb11-9" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="cn"&gt;Ok&lt;/span&gt;(s) &lt;span class="co"&gt;// all good, return a string inside a `Result` context&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb11-10"&gt;&lt;a href="#cb11-10" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb11-11"&gt;&lt;a href="#cb11-11" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb11-12"&gt;&lt;a href="#cb11-12" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; main() &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb11-13"&gt;&lt;a href="#cb11-13" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="co"&gt;// `contents` is an enum known as Result:&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb11-14"&gt;&lt;a href="#cb11-14" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;let&lt;/span&gt; contents &lt;span class="op"&gt;=&lt;/span&gt; foo()&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb11-15"&gt;&lt;a href="#cb11-15" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;match&lt;/span&gt; contents &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb11-16"&gt;&lt;a href="#cb11-16" aria-hidden="true"&gt;&lt;/a&gt;        &lt;span class="cn"&gt;Ok&lt;/span&gt;(c) &lt;span class="op"&gt;=&amp;gt;&lt;/span&gt; &lt;span class="pp"&gt;println!&lt;/span&gt;(c)&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb11-17"&gt;&lt;a href="#cb11-17" aria-hidden="true"&gt;&lt;/a&gt;        &lt;span class="cn"&gt;Err&lt;/span&gt;(e) &lt;span class="op"&gt;=&amp;gt;&lt;/span&gt; &lt;span class="pp"&gt;eprintln!&lt;/span&gt;(e)&lt;/span&gt;
&lt;span id="cb11-18"&gt;&lt;a href="#cb11-18" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb11-19"&gt;&lt;a href="#cb11-19" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;h3 id="conclusion"&gt;Conclusion&lt;/h3&gt;
&lt;p&gt;I did not want to conclude without talking about stylistic choices, lack of metaprogramming, bizzare export rules, but, I am too busy converting my &lt;code&gt;interface{}&lt;/code&gt; types into actual generic code for Go v2.&lt;/p&gt;</description>
<link>https://peppe.rs/posts/gripes_with_go/</link>
<pubDate>Sat, 01 Aug 2020 11:55:00 +0000</pubDate>
<guid>https://peppe.rs/posts/gripes_with_go/</guid>
</item>
<item>
<title>Turing Complete Type Systems</title>
<description>&lt;p&gt;Rust’s type system is Turing complete:&lt;/p&gt;
&lt;ul&gt;
&lt;li&gt;&lt;a href="https://github.com/doctorn/trait-eval/"&gt;FizzBuzz with Rust Traits&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href="https://github.com/Ashymad/fortraith"&gt;A Forth implementation with Rust Traits&lt;/a&gt;&lt;/li&gt;
&lt;/ul&gt;
&lt;p&gt;It is impossible to determine if a program written in a generally Turing complete system will ever stop. That is, it is impossible to write a program &lt;code&gt;f&lt;/code&gt; that determines if a program &lt;code&gt;g&lt;/code&gt;, where &lt;code&gt;g&lt;/code&gt; is written in a Turing complete programming language, will ever halt. The &lt;a href="https://en.wikipedia.org/wiki/Halting_problem"&gt;Halting Problem&lt;/a&gt; is in fact, an &lt;a href="https://en.wikipedia.org/wiki/Undecidable_problem"&gt;undecidable problem&lt;/a&gt;.&lt;/p&gt;
&lt;p&gt;&lt;em&gt;How is any of this relevant?&lt;/em&gt;&lt;/p&gt;
&lt;p&gt;Rust performs compile-time type inference. The type checker, in turn, compiles and infers types, I would describe it as a compiler inside a compiler. It is possible that &lt;code&gt;rustc&lt;/code&gt; may never finish compiling your Rust program! I lied, &lt;code&gt;rustc&lt;/code&gt; stops after a while, after hitting the recursion limit.&lt;/p&gt;
&lt;p&gt;I understand that this post lacks content.&lt;/p&gt;</description>
<link>https://peppe.rs/posts/turing_complete_type_systems/</link>
<pubDate>Wed, 17 Jun 2020 18:30:00 +0000</pubDate>
<guid>https://peppe.rs/posts/turing_complete_type_systems/</guid>
</item>
<item>
<title>Auto-currying Rust Functions</title>
<description>&lt;p&gt;This post contains a gentle introduction to procedural macros in Rust and a guide to writing a procedural macro to curry Rust functions. The source code for the entire library can be found &lt;a href="https://github.com/nerdypepper/cutlass"&gt;here&lt;/a&gt;. It is also available on &lt;a href="https://crates.io/crates/cutlass"&gt;crates.io&lt;/a&gt;.&lt;/p&gt;
&lt;p&gt;The following links might prove to be useful before getting started:&lt;/p&gt;
&lt;ul&gt;
&lt;li&gt;&lt;a href="https://doc.rust-lang.org/reference/procedural-macros.html"&gt;Procedural Macros&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href="https://en.wikipedia.org/wiki/Currying"&gt;Currying&lt;/a&gt;&lt;/li&gt;
&lt;/ul&gt;
&lt;p&gt;Or you can pretend you read them, because I have included a primer here :)&lt;/p&gt;
&lt;h3 id="contents"&gt;Contents&lt;/h3&gt;
&lt;ol type="1"&gt;
&lt;li&gt;&lt;a href="#currying"&gt;Currying&lt;/a&gt;&lt;br /&gt;
&lt;/li&gt;
&lt;li&gt;&lt;a href="#procedural-macros"&gt;Procedural Macros&lt;/a&gt;&lt;br /&gt;
&lt;/li&gt;
&lt;li&gt;&lt;a href="#definitions"&gt;Definitions&lt;/a&gt;&lt;br /&gt;
&lt;/li&gt;
&lt;li&gt;&lt;a href="#refinement"&gt;Refinement&lt;/a&gt;&lt;br /&gt;
&lt;/li&gt;
&lt;li&gt;&lt;a href="#the-in-betweens"&gt;The In-betweens&lt;/a&gt;&lt;br /&gt;
     5.1 &lt;a href="#dependencies"&gt;Dependencies&lt;/a&gt;&lt;br /&gt;
     5.2 &lt;a href="#the-attribute-macro"&gt;The attribute macro&lt;/a&gt;&lt;br /&gt;
     5.3 &lt;a href="#function-body"&gt;Function Body&lt;/a&gt;&lt;br /&gt;
     5.4 &lt;a href="#function-signature"&gt;Function Signature&lt;/a&gt;&lt;br /&gt;
     5.5 &lt;a href="#getting-it-together"&gt;Getting it together&lt;/a&gt;&lt;br /&gt;
&lt;/li&gt;
&lt;li&gt;&lt;a href="#debugging-and-testing"&gt;Debugging and Testing&lt;/a&gt;&lt;br /&gt;
&lt;/li&gt;
&lt;li&gt;&lt;a href="#notes"&gt;Notes&lt;/a&gt;&lt;br /&gt;
&lt;/li&gt;
&lt;li&gt;&lt;a href="#conclusion"&gt;Conclusion&lt;/a&gt;&lt;/li&gt;
&lt;/ol&gt;
&lt;h3 id="currying"&gt;Currying&lt;/h3&gt;
&lt;p&gt;Currying is the process of transformation of a function call like &lt;code&gt;f(a, b, c)&lt;/code&gt; to &lt;code&gt;f(a)(b)(c)&lt;/code&gt;. A curried function returns a concrete value only when it receives all its arguments! If it does recieve an insufficient amount of arguments, say 1 of 3, it returns a &lt;em&gt;curried function&lt;/em&gt;, that returns after receiving 2 arguments.&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;curry(f(a, b, c)) = h(a)(b)(c)

h(x) = g   &amp;lt;- curried function that takes upto 2 args (g)
g(y) = k   &amp;lt;- curried function that takes upto 1 arg (k)
k(z) = v   &amp;lt;- a value (v)

Keen readers will conclude the following,
h(x)(y)(z) = g(y)(z) = k(z) = v&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Mathematically, if &lt;code&gt;f&lt;/code&gt; is a function that takes two arguments &lt;code&gt;x&lt;/code&gt; and &lt;code&gt;y&lt;/code&gt;, such that &lt;code&gt;x ϵ X&lt;/code&gt;, and &lt;code&gt;y ϵ Y&lt;/code&gt; , we write it as:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;f: (X × Y) -&amp;gt; Z&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;where &lt;code&gt;×&lt;/code&gt; denotes the Cartesian product of set &lt;code&gt;X&lt;/code&gt; and &lt;code&gt;Y&lt;/code&gt;, and curried &lt;code&gt;f&lt;/code&gt; (denoted by &lt;code&gt;h&lt;/code&gt; here) is written as:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;h: X -&amp;gt; (Y -&amp;gt; Z)&lt;/code&gt;&lt;/pre&gt;
&lt;h3 id="procedural-macros"&gt;Procedural Macros&lt;/h3&gt;
&lt;p&gt;These are functions that take code as input and spit out modified code as output. Powerful stuff. Rust has three kinds of proc-macros:&lt;/p&gt;
&lt;ul&gt;
&lt;li&gt;Function like macros&lt;br /&gt;
&lt;/li&gt;
&lt;li&gt;Derive macros: &lt;code&gt;#[derive(...)]&lt;/code&gt;, used to automatically implement traits for structs/enums&lt;br /&gt;
&lt;/li&gt;
&lt;li&gt;and Attribute macros: &lt;code&gt;#[test]&lt;/code&gt;, usually slapped onto functions&lt;/li&gt;
&lt;/ul&gt;
&lt;p&gt;We will be using Attribute macros to convert a Rust function into a curried Rust function, which we should be able to call via: &lt;code&gt;function(arg1)(arg2)&lt;/code&gt;.&lt;/p&gt;
&lt;h3 id="definitions"&gt;Definitions&lt;/h3&gt;
&lt;p&gt;Being respectable programmers, we define the input to and the output from our proc-macro. Here’s a good non-trivial function to start out with:&lt;/p&gt;
&lt;div class="sourceCode" id="cb4"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb4-1"&gt;&lt;a href="#cb4-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; add(x&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; y&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; z&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb4-2"&gt;&lt;a href="#cb4-2" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;return&lt;/span&gt; x &lt;span class="op"&gt;+&lt;/span&gt; y &lt;span class="op"&gt;+&lt;/span&gt; z&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb4-3"&gt;&lt;a href="#cb4-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Hmm, what would our output look like? What should our proc-macro generate ideally? Well, if we understood currying correctly, we should accept an argument and return a function that accepts an argument and returns … you get the point. Something like this should do:&lt;/p&gt;
&lt;div class="sourceCode" id="cb5"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb5-1"&gt;&lt;a href="#cb5-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; add_curried1(x&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="op"&gt;?&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb5-2"&gt;&lt;a href="#cb5-2" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;return&lt;/span&gt; &lt;span class="kw"&gt;fn&lt;/span&gt; add_curried2 (y&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="op"&gt;?&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb5-3"&gt;&lt;a href="#cb5-3" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;return&lt;/span&gt; &lt;span class="kw"&gt;fn&lt;/span&gt; add_curried3 (z&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb5-4"&gt;&lt;a href="#cb5-4" aria-hidden="true"&gt;&lt;/a&gt;      &lt;span class="kw"&gt;return&lt;/span&gt; x &lt;span class="op"&gt;+&lt;/span&gt; y &lt;span class="op"&gt;+&lt;/span&gt; z&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb5-5"&gt;&lt;a href="#cb5-5" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb5-6"&gt;&lt;a href="#cb5-6" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb5-7"&gt;&lt;a href="#cb5-7" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;A couple of things to note:&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Return types&lt;/strong&gt;&lt;br /&gt;
We have placed &lt;code&gt;?&lt;/code&gt;s in place of return types. Let’s try to fix that. &lt;code&gt;add_curried3&lt;/code&gt; returns the ‘value’, so &lt;code&gt;u32&lt;/code&gt; is accurate. &lt;code&gt;add_curried2&lt;/code&gt; returns &lt;code&gt;add_curried3&lt;/code&gt;. What is the type of &lt;code&gt;add_curried3&lt;/code&gt;? It is a function that takes in a &lt;code&gt;u32&lt;/code&gt; and returns a &lt;code&gt;u32&lt;/code&gt;. So a &lt;code&gt;fn(u32) -&amp;gt; u32&lt;/code&gt; will do right? No, I’ll explain why in the next point, but for now, we will make use of the &lt;code&gt;Fn&lt;/code&gt; trait, our return type is &lt;code&gt;impl Fn(u32) -&amp;gt; u32&lt;/code&gt;. This basically tells the compiler that we will be returning something function-like, a.k.a, behaves like a &lt;code&gt;Fn&lt;/code&gt;. Cool!&lt;/p&gt;
&lt;p&gt;If you have been following along, you should be able to tell that the return type of &lt;code&gt;add_curried1&lt;/code&gt; is:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;impl Fn(u32) -&amp;gt; (impl Fn(u32) -&amp;gt; u32)&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;We can drop the parentheses because &lt;code&gt;-&amp;gt;&lt;/code&gt; is right associative:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;impl Fn(u32) -&amp;gt; impl Fn(u32) -&amp;gt; u32
&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;&lt;strong&gt;Accessing environment&lt;/strong&gt;&lt;br /&gt;
A function cannot access it’s environment. Our solution will not work. &lt;code&gt;add_curried3&lt;/code&gt; attempts to access &lt;code&gt;x&lt;/code&gt;, which is not allowed! A closure&lt;a href="#fn1" class="footnote-ref" id="fnref1" role="doc-noteref"&gt;&lt;sup&gt;1&lt;/sup&gt;&lt;/a&gt; however, can. If we are returning a closure, our return type must be &lt;code&gt;impl Fn&lt;/code&gt;, and not &lt;code&gt;fn&lt;/code&gt;. The difference between the &lt;code&gt;Fn&lt;/code&gt; trait and function pointers is beyond the scope of this post.&lt;/p&gt;
&lt;h3 id="refinement"&gt;Refinement&lt;/h3&gt;
&lt;p&gt;Armed with knowledge, we refine our expected output, this time, employing closures:&lt;/p&gt;
&lt;div class="sourceCode" id="cb8"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb8-1"&gt;&lt;a href="#cb8-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; add(x&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb8-2"&gt;&lt;a href="#cb8-2" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;return&lt;/span&gt; &lt;span class="kw"&gt;move&lt;/span&gt; &lt;span class="op"&gt;|&lt;/span&gt;y&lt;span class="op"&gt;|&lt;/span&gt; &lt;span class="kw"&gt;move&lt;/span&gt; &lt;span class="op"&gt;|&lt;/span&gt;z&lt;span class="op"&gt;|&lt;/span&gt; x &lt;span class="op"&gt;+&lt;/span&gt; y &lt;span class="op"&gt;+&lt;/span&gt; z&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb8-3"&gt;&lt;a href="#cb8-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Alas, that does not compile either! It errors out with the following message:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;error[E0562]: `impl Trait` not allowed outside of function
and inherent method return types
  --&amp;gt; src/main.rs:17:37
   |
   | fn add(x: u32) -&amp;gt; impl Fn(u32) -&amp;gt; impl Fn(u32) -&amp;gt; u32
   |                                   ^^^^^^^^^^^^^^^^^^^
&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;You are allowed to return an &lt;code&gt;impl Fn&lt;/code&gt; only inside a function. We are currently returning it from another return! Or at least, that was the most I could make out of the error message.&lt;/p&gt;
&lt;p&gt;We are going to have to cheat a bit to fix this issue; with type aliases and a convenient nightly feature &lt;a href="#fn2" class="footnote-ref" id="fnref2" role="doc-noteref"&gt;&lt;sup&gt;2&lt;/sup&gt;&lt;/a&gt;:&lt;/p&gt;
&lt;div class="sourceCode" id="cb10"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb10-1"&gt;&lt;a href="#cb10-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="at"&gt;#![&lt;/span&gt;feature&lt;span class="at"&gt;(&lt;/span&gt;type_alias_impl_trait&lt;span class="at"&gt;)]&lt;/span&gt;  &lt;span class="co"&gt;// allows us to use `impl Fn` in type aliases!&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb10-2"&gt;&lt;a href="#cb10-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb10-3"&gt;&lt;a href="#cb10-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T0 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;;&lt;/span&gt;                 &lt;span class="co"&gt;// the return value when zero args are to be applied&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb10-4"&gt;&lt;a href="#cb10-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T1 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; T0&lt;span class="op"&gt;;&lt;/span&gt;  &lt;span class="co"&gt;// the return value when one arg is to be applied&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb10-5"&gt;&lt;a href="#cb10-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T2 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; T1&lt;span class="op"&gt;;&lt;/span&gt;  &lt;span class="co"&gt;// the return value when two args are to be applied&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb10-6"&gt;&lt;a href="#cb10-6" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb10-7"&gt;&lt;a href="#cb10-7" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; add(x&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; T2 &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb10-8"&gt;&lt;a href="#cb10-8" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;return&lt;/span&gt; &lt;span class="kw"&gt;move&lt;/span&gt; &lt;span class="op"&gt;|&lt;/span&gt;y&lt;span class="op"&gt;|&lt;/span&gt; &lt;span class="kw"&gt;move&lt;/span&gt; &lt;span class="op"&gt;|&lt;/span&gt;z&lt;span class="op"&gt;|&lt;/span&gt; x &lt;span class="op"&gt;+&lt;/span&gt; y &lt;span class="op"&gt;+&lt;/span&gt; z&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb10-9"&gt;&lt;a href="#cb10-9" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Drop that into a cargo project, call &lt;code&gt;add(4)(5)(6)&lt;/code&gt;, cross your fingers, and run &lt;code&gt;cargo +nightly run&lt;/code&gt;. You should see a 15 unless you forgot to print it!&lt;/p&gt;
&lt;h3 id="the-in-betweens"&gt;The In-Betweens&lt;/h3&gt;
&lt;p&gt;Let us write the magical bits that take us from function to curried function.&lt;/p&gt;
&lt;p&gt;Initialize your workspace with &lt;code&gt;cargo new --lib currying&lt;/code&gt;. Proc-macro crates are libraries with exactly one export, the macro itself. Add a &lt;code&gt;tests&lt;/code&gt; directory to your crate root. Your directory should look something like this:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;.
├── Cargo.toml
├── src
│   └── lib.rs
└── tests
    └── smoke.rs&lt;/code&gt;&lt;/pre&gt;
&lt;h4 id="dependencies"&gt;Dependencies&lt;/h4&gt;
&lt;p&gt;We will be using a total of 3 external crates:&lt;/p&gt;
&lt;ul&gt;
&lt;li&gt;&lt;a href="https://docs.rs/proc-macro2/1.0.12/proc_macro2/"&gt;proc_macro2&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href="https://docs.rs/syn/1.0.18/syn/index.html"&gt;syn&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href="https://docs.rs/quote/1.0.4/quote/index.html"&gt;quote&lt;/a&gt;&lt;/li&gt;
&lt;/ul&gt;
&lt;p&gt;Here’s a sample &lt;code&gt;Cargo.toml&lt;/code&gt;:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;# Cargo.toml

[dependencies]
proc-macro2 = &amp;quot;1.0.9&amp;quot;
quote = &amp;quot;1.0&amp;quot;

[dependencies.syn]
version = &amp;quot;1.0&amp;quot;
features = [&amp;quot;full&amp;quot;]

[lib]
proc-macro = true  # this is important!&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;We will be using an external &lt;code&gt;proc-macro2&lt;/code&gt; crate as well as an internal &lt;code&gt;proc-macro&lt;/code&gt; crate. Not confusing at all!&lt;/p&gt;
&lt;h4 id="the-attribute-macro"&gt;The attribute macro&lt;/h4&gt;
&lt;p&gt;Drop this into &lt;code&gt;src/lib.rs&lt;/code&gt;, to get the ball rolling.&lt;/p&gt;
&lt;div class="sourceCode" id="cb13"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb13-1"&gt;&lt;a href="#cb13-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// src/lib.rs&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb13-2"&gt;&lt;a href="#cb13-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb13-3"&gt;&lt;a href="#cb13-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;use&lt;/span&gt; &lt;span class="pp"&gt;proc_macro::&lt;/span&gt;TokenStream&lt;span class="op"&gt;;&lt;/span&gt;  &lt;span class="co"&gt;// 1&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb13-4"&gt;&lt;a href="#cb13-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;use&lt;/span&gt; &lt;span class="pp"&gt;quote::&lt;/span&gt;quote&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb13-5"&gt;&lt;a href="#cb13-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;use&lt;/span&gt; &lt;span class="pp"&gt;syn::&lt;/span&gt;&lt;span class="op"&gt;{&lt;/span&gt;parse_macro_input&lt;span class="op"&gt;,&lt;/span&gt; ItemFn&lt;span class="op"&gt;};&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb13-6"&gt;&lt;a href="#cb13-6" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb13-7"&gt;&lt;a href="#cb13-7" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="at"&gt;#[&lt;/span&gt;proc_macro_attribute&lt;span class="at"&gt;]&lt;/span&gt;   &lt;span class="co"&gt;// 2&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb13-8"&gt;&lt;a href="#cb13-8" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;pub&lt;/span&gt; &lt;span class="kw"&gt;fn&lt;/span&gt; curry(_attr&lt;span class="op"&gt;:&lt;/span&gt; TokenStream&lt;span class="op"&gt;,&lt;/span&gt; item&lt;span class="op"&gt;:&lt;/span&gt; TokenStream) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; TokenStream &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb13-9"&gt;&lt;a href="#cb13-9" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; parsed &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="pp"&gt;parse_macro_input!&lt;/span&gt;(item &lt;span class="kw"&gt;as&lt;/span&gt; ItemFn)&lt;span class="op"&gt;;&lt;/span&gt;  &lt;span class="co"&gt;// 3&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb13-10"&gt;&lt;a href="#cb13-10" aria-hidden="true"&gt;&lt;/a&gt;  generate_curry(parsed)&lt;span class="op"&gt;.&lt;/span&gt;into()  &lt;span class="co"&gt;// 4&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb13-11"&gt;&lt;a href="#cb13-11" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb13-12"&gt;&lt;a href="#cb13-12" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb13-13"&gt;&lt;a href="#cb13-13" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; generate_curry(parsed&lt;span class="op"&gt;:&lt;/span&gt; ItemFn) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="pp"&gt;proc_macro2::&lt;/span&gt;TokenStream &lt;span class="op"&gt;{}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;&lt;strong&gt;1. Imports&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;A &lt;code&gt;Tokenstream&lt;/code&gt; holds (hopefully valid) Rust code, this is the type of our input and output. Note that we are importing this type from &lt;code&gt;proc_macro&lt;/code&gt; and not &lt;code&gt;proc_macro2&lt;/code&gt;.&lt;/p&gt;
&lt;p&gt;&lt;code&gt;quote!&lt;/code&gt; from the &lt;code&gt;quote&lt;/code&gt; crate is a macro that allows us to quickly produce &lt;code&gt;TokenStream&lt;/code&gt;s. Much like the LISP &lt;code&gt;quote&lt;/code&gt; procedure, you can use the &lt;code&gt;quote!&lt;/code&gt; macro for symbolic transformations.&lt;/p&gt;
&lt;p&gt;&lt;code&gt;ItemFn&lt;/code&gt; from the &lt;code&gt;syn&lt;/code&gt; crate holds the parsed &lt;code&gt;TokenStream&lt;/code&gt; of a Rust function. &lt;code&gt;parse_macro_input!&lt;/code&gt; is a helper macro provided by &lt;code&gt;syn&lt;/code&gt;.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;2. The lone export&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;Annotate the only &lt;code&gt;pub&lt;/code&gt; of our crate with &lt;code&gt;#[proc_macro_attribute]&lt;/code&gt;. This tells rustc that &lt;code&gt;curry&lt;/code&gt; is a procedural macro, and allows us to use it as &lt;code&gt;#[crate_name::curry]&lt;/code&gt; in other crates. Note the signature of the &lt;code&gt;curry&lt;/code&gt; function. &lt;code&gt;_attr&lt;/code&gt; is the &lt;code&gt;TokenStream&lt;/code&gt; representing the attribute itself, &lt;code&gt;item&lt;/code&gt; refers to the thing we slapped our macro into, in this case a function (like &lt;code&gt;add&lt;/code&gt;). The return value is a modified &lt;code&gt;TokenStream&lt;/code&gt;, this will contain our curried version of &lt;code&gt;add&lt;/code&gt;.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;3. The helper macro&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;A &lt;code&gt;TokenStream&lt;/code&gt; is a little hard to work with, which is why we have the &lt;code&gt;syn&lt;/code&gt; crate, which provides types to represent Rust tokens. An &lt;code&gt;RArrow&lt;/code&gt; struct to represent the return arrow on a function and so on. One of those types is &lt;code&gt;ItemFn&lt;/code&gt;, that represents an entire Rust function. The &lt;code&gt;parse_macro_input!&lt;/code&gt; automatically puts the input to our macro into an &lt;code&gt;ItemFn&lt;/code&gt;. What a gentleman!&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;4. Returning &lt;code&gt;TokenStream&lt;/code&gt;s &lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;We haven’t filled in &lt;code&gt;generate_curry&lt;/code&gt; yet, but we can see that it returns a &lt;code&gt;proc_macro2::TokenStream&lt;/code&gt; and not a &lt;code&gt;proc_macro::TokenStream&lt;/code&gt;, so drop a &lt;code&gt;.into()&lt;/code&gt; to convert it.&lt;/p&gt;
&lt;p&gt;Lets move on, and fill in &lt;code&gt;generate_curry&lt;/code&gt;, I would suggest keeping the documentation for &lt;a href="https://docs.rs/syn/1.0.19/syn/struct.ItemFn.html"&gt;&lt;code&gt;syn::ItemFn&lt;/code&gt;&lt;/a&gt; and &lt;a href="https://docs.rs/syn/1.0.19/syn/struct.Signature.html"&gt;&lt;code&gt;syn::Signature&lt;/code&gt;&lt;/a&gt; open.&lt;/p&gt;
&lt;div class="sourceCode" id="cb14"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb14-1"&gt;&lt;a href="#cb14-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// src/lib.rs&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb14-2"&gt;&lt;a href="#cb14-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb14-3"&gt;&lt;a href="#cb14-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; generate_curry(parsed&lt;span class="op"&gt;:&lt;/span&gt; ItemFn) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="pp"&gt;proc_macro2::&lt;/span&gt;TokenStream &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb14-4"&gt;&lt;a href="#cb14-4" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; fn_body &lt;span class="op"&gt;=&lt;/span&gt; parsed&lt;span class="op"&gt;.&lt;/span&gt;block&lt;span class="op"&gt;;&lt;/span&gt;      &lt;span class="co"&gt;// function body&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb14-5"&gt;&lt;a href="#cb14-5" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; sig &lt;span class="op"&gt;=&lt;/span&gt; parsed&lt;span class="op"&gt;.&lt;/span&gt;sig&lt;span class="op"&gt;;&lt;/span&gt;            &lt;span class="co"&gt;// function signature&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb14-6"&gt;&lt;a href="#cb14-6" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; vis &lt;span class="op"&gt;=&lt;/span&gt; parsed&lt;span class="op"&gt;.&lt;/span&gt;vis&lt;span class="op"&gt;;&lt;/span&gt;            &lt;span class="co"&gt;// visibility, pub or not&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb14-7"&gt;&lt;a href="#cb14-7" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; fn_name &lt;span class="op"&gt;=&lt;/span&gt; sig&lt;span class="op"&gt;.&lt;/span&gt;ident&lt;span class="op"&gt;;&lt;/span&gt;         &lt;span class="co"&gt;// function name/identifier&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb14-8"&gt;&lt;a href="#cb14-8" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; fn_args &lt;span class="op"&gt;=&lt;/span&gt; sig&lt;span class="op"&gt;.&lt;/span&gt;inputs&lt;span class="op"&gt;;&lt;/span&gt;        &lt;span class="co"&gt;// comma separated args&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb14-9"&gt;&lt;a href="#cb14-9" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; fn_return_type &lt;span class="op"&gt;=&lt;/span&gt; sig&lt;span class="op"&gt;.&lt;/span&gt;output&lt;span class="op"&gt;;&lt;/span&gt; &lt;span class="co"&gt;// return type&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb14-10"&gt;&lt;a href="#cb14-10" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;We are simply extracting the bits of the function, we will be reusing the original function’s visibility and name. Take a look at what &lt;code&gt;syn::Signature&lt;/code&gt; can tell us about a function:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;                       .-- syn::Ident (ident)
                      /
                 fn add(x: u32, y: u32) -&amp;gt; u32
  (fn_token)      /     ~~~~~~~,~~~~~~  ~~~~~~
syn::token::Fn --&amp;#39;            /               \       (output)
                             &amp;#39;                 `- syn::ReturnType
             Punctuated&amp;lt;FnArg, Comma&amp;gt; (inputs)&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Enough analysis, lets produce our first bit of Rust code.&lt;/p&gt;
&lt;h4 id="function-body"&gt;Function Body&lt;/h4&gt;
&lt;p&gt;Recall that the body of a curried &lt;code&gt;add&lt;/code&gt; should look like this:&lt;/p&gt;
&lt;div class="sourceCode" id="cb16"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb16-1"&gt;&lt;a href="#cb16-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;return&lt;/span&gt; &lt;span class="kw"&gt;move&lt;/span&gt; &lt;span class="op"&gt;|&lt;/span&gt;y&lt;span class="op"&gt;|&lt;/span&gt; &lt;span class="kw"&gt;move&lt;/span&gt; &lt;span class="op"&gt;|&lt;/span&gt;z&lt;span class="op"&gt;|&lt;/span&gt; x &lt;span class="op"&gt;+&lt;/span&gt; y &lt;span class="op"&gt;+&lt;/span&gt; z&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;And in general:&lt;/p&gt;
&lt;div class="sourceCode" id="cb17"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb17-1"&gt;&lt;a href="#cb17-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;return&lt;/span&gt; &lt;span class="kw"&gt;move&lt;/span&gt; &lt;span class="op"&gt;|&lt;/span&gt;arg2&lt;span class="op"&gt;|&lt;/span&gt; &lt;span class="kw"&gt;move&lt;/span&gt; &lt;span class="op"&gt;|&lt;/span&gt;arg3&lt;span class="op"&gt;|&lt;/span&gt; &lt;span class="op"&gt;...&lt;/span&gt; &lt;span class="op"&gt;|&lt;/span&gt;argN&lt;span class="op"&gt;|&lt;/span&gt; &lt;span class="op"&gt;&amp;lt;&lt;/span&gt;function body here&lt;span class="op"&gt;&amp;gt;&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;We already have the function’s body, provided by &lt;code&gt;fn_body&lt;/code&gt;, in our &lt;code&gt;generate_curry&lt;/code&gt; function. All that’s left to add is the &lt;code&gt;move |arg2| move |arg3| ...&lt;/code&gt; stuff, for which we need to extract the argument identifiers (doc: &lt;a href="https://docs.rs/syn/1.0.18/syn/punctuated/struct.Punctuated.html"&gt;Punctuated&lt;/a&gt;, &lt;a href="https://docs.rs/syn/1.0.18/syn/enum.FnArg.html"&gt;FnArg&lt;/a&gt;, &lt;a href="https://docs.rs/syn/1.0.18/syn/struct.PatType.html"&gt;PatType&lt;/a&gt;):&lt;/p&gt;
&lt;div class="sourceCode" id="cb18"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb18-1"&gt;&lt;a href="#cb18-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// src/lib.rs&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb18-2"&gt;&lt;a href="#cb18-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;use&lt;/span&gt; &lt;span class="pp"&gt;syn::punctuated::&lt;/span&gt;Punctuated&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb18-3"&gt;&lt;a href="#cb18-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;use&lt;/span&gt; &lt;span class="pp"&gt;syn::&lt;/span&gt;&lt;span class="op"&gt;{&lt;/span&gt;parse_macro_input&lt;span class="op"&gt;,&lt;/span&gt; FnArg&lt;span class="op"&gt;,&lt;/span&gt; Pat&lt;span class="op"&gt;,&lt;/span&gt; ItemFn&lt;span class="op"&gt;,&lt;/span&gt; Block&lt;span class="op"&gt;};&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb18-4"&gt;&lt;a href="#cb18-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb18-5"&gt;&lt;a href="#cb18-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; extract_arg_idents(fn_args&lt;span class="op"&gt;:&lt;/span&gt; Punctuated&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;FnArg&lt;span class="op"&gt;,&lt;/span&gt; &lt;span class="pp"&gt;syn::token::&lt;/span&gt;Comma&lt;span class="op"&gt;&amp;gt;&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;Vec&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;&lt;span class="dt"&gt;Box&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;Pat&lt;span class="op"&gt;&amp;gt;&amp;gt;&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt; &lt;/span&gt;
&lt;span id="cb18-6"&gt;&lt;a href="#cb18-6" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;return&lt;/span&gt; fn_args&lt;span class="op"&gt;.&lt;/span&gt;into_iter()&lt;span class="op"&gt;.&lt;/span&gt;map(extract_arg_pat)&lt;span class="op"&gt;.&lt;/span&gt;&lt;span class="pp"&gt;collect::&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;&lt;span class="dt"&gt;Vec&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;_&lt;span class="op"&gt;&amp;gt;&amp;gt;&lt;/span&gt;()&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb18-7"&gt;&lt;a href="#cb18-7" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Alright, so we are iterating over function args (&lt;code&gt;Punctuated&lt;/code&gt; is a collection that you can iterate over) and mapping an &lt;code&gt;extract_arg_pat&lt;/code&gt; to every item. What’s &lt;code&gt;extract_arg_pat&lt;/code&gt;?&lt;/p&gt;
&lt;div class="sourceCode" id="cb19"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb19-1"&gt;&lt;a href="#cb19-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// src/lib.rs&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb19-2"&gt;&lt;a href="#cb19-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb19-3"&gt;&lt;a href="#cb19-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; extract_arg_pat(a&lt;span class="op"&gt;:&lt;/span&gt; FnArg) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;Box&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;Pat&lt;span class="op"&gt;&amp;gt;&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb19-4"&gt;&lt;a href="#cb19-4" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;match&lt;/span&gt; a &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb19-5"&gt;&lt;a href="#cb19-5" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="pp"&gt;FnArg::&lt;/span&gt;Typed(p) &lt;span class="op"&gt;=&amp;gt;&lt;/span&gt; p&lt;span class="op"&gt;.&lt;/span&gt;pat&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb19-6"&gt;&lt;a href="#cb19-6" aria-hidden="true"&gt;&lt;/a&gt;    _ &lt;span class="op"&gt;=&amp;gt;&lt;/span&gt; &lt;span class="pp"&gt;panic!&lt;/span&gt;(&lt;span class="st"&gt;&amp;quot;Not supported on types with `self`!&amp;quot;&lt;/span&gt;)&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb19-7"&gt;&lt;a href="#cb19-7" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb19-8"&gt;&lt;a href="#cb19-8" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;&lt;code&gt;FnArg&lt;/code&gt; is an enum type as you might have guessed. The &lt;code&gt;Typed&lt;/code&gt; variant encompasses args that are written as &lt;code&gt;name: type&lt;/code&gt; and the other variant, &lt;code&gt;Reciever&lt;/code&gt; refers to &lt;code&gt;self&lt;/code&gt; types. Ignore those for now, keep it simple.&lt;/p&gt;
&lt;p&gt;Every &lt;code&gt;FnArg::Typed&lt;/code&gt; value contains a &lt;code&gt;pat&lt;/code&gt;, which is in essence, the name of the argument. The type of the arg is accessible via &lt;code&gt;p.ty&lt;/code&gt; (we will be using this later).&lt;/p&gt;
&lt;p&gt;With that done, we should be able to write the codegen for the function body:&lt;/p&gt;
&lt;div class="sourceCode" id="cb20"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb20-1"&gt;&lt;a href="#cb20-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// src/lib.rs&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb20-2"&gt;&lt;a href="#cb20-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb20-3"&gt;&lt;a href="#cb20-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; generate_body(fn_args&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="op"&gt;&amp;amp;&lt;/span&gt;[&lt;span class="dt"&gt;Box&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;Pat&lt;span class="op"&gt;&amp;gt;&lt;/span&gt;]&lt;span class="op"&gt;,&lt;/span&gt; body&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;Box&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;Block&lt;span class="op"&gt;&amp;gt;&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="pp"&gt;proc_macro2::&lt;/span&gt;TokenStream &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb20-4"&gt;&lt;a href="#cb20-4" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="pp"&gt;quote!&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb20-5"&gt;&lt;a href="#cb20-5" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;return&lt;/span&gt; #( &lt;span class="kw"&gt;move&lt;/span&gt; &lt;span class="op"&gt;|&lt;/span&gt;#fn_args&lt;span class="op"&gt;|&lt;/span&gt;  )&lt;span class="op"&gt;*&lt;/span&gt; #body&lt;/span&gt;
&lt;span id="cb20-6"&gt;&lt;a href="#cb20-6" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb20-7"&gt;&lt;a href="#cb20-7" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;That is some scary looking syntax! Allow me to explain. The &lt;code&gt;quote!{ ... }&lt;/code&gt; returns a &lt;code&gt;proc_macro2::TokenStream&lt;/code&gt;, if we wrote &lt;code&gt;quote!{ let x = 1 + 2; }&lt;/code&gt;, it wouldn’t create a new variable &lt;code&gt;x&lt;/code&gt; with value 3, it would literally produce a stream of tokens with that expression.&lt;/p&gt;
&lt;p&gt;The &lt;code&gt;#&lt;/code&gt; enables variable interpolation. &lt;code&gt;#body&lt;/code&gt; will look for &lt;code&gt;body&lt;/code&gt; in the current scope, take its value, and insert it in the returned &lt;code&gt;TokenStream&lt;/code&gt;. Kinda like quasi quoting in LISPs, you have written one.&lt;/p&gt;
&lt;p&gt;What about &lt;code&gt;#( move |#fn_args| )*&lt;/code&gt;? That is repetition. &lt;code&gt;quote&lt;/code&gt; iterates through &lt;code&gt;fn_args&lt;/code&gt;, and drops a &lt;code&gt;move&lt;/code&gt; behind each one, it then places pipes (&lt;code&gt;|&lt;/code&gt;), around it.&lt;/p&gt;
&lt;p&gt;Let us test our first bit of codegen! Modify &lt;code&gt;generate_curry&lt;/code&gt; like so:&lt;/p&gt;
&lt;div class="sourceCode" id="cb21"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb21-1"&gt;&lt;a href="#cb21-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// src/lib.rs&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb21-2"&gt;&lt;a href="#cb21-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb21-3"&gt;&lt;a href="#cb21-3" aria-hidden="true"&gt;&lt;/a&gt; &lt;span class="kw"&gt;fn&lt;/span&gt; generate_curry(parsed&lt;span class="op"&gt;:&lt;/span&gt; ItemFn) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; TokenStream &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb21-4"&gt;&lt;a href="#cb21-4" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; fn_body &lt;span class="op"&gt;=&lt;/span&gt; parsed&lt;span class="op"&gt;.&lt;/span&gt;block&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb21-5"&gt;&lt;a href="#cb21-5" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; sig &lt;span class="op"&gt;=&lt;/span&gt; parsed&lt;span class="op"&gt;.&lt;/span&gt;sig&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb21-6"&gt;&lt;a href="#cb21-6" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; vis &lt;span class="op"&gt;=&lt;/span&gt; parsed&lt;span class="op"&gt;.&lt;/span&gt;vis&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb21-7"&gt;&lt;a href="#cb21-7" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; fn_name &lt;span class="op"&gt;=&lt;/span&gt; sig&lt;span class="op"&gt;.&lt;/span&gt;ident&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb21-8"&gt;&lt;a href="#cb21-8" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; fn_args &lt;span class="op"&gt;=&lt;/span&gt; sig&lt;span class="op"&gt;.&lt;/span&gt;inputs&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb21-9"&gt;&lt;a href="#cb21-9" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; fn_return_type &lt;span class="op"&gt;=&lt;/span&gt; sig&lt;span class="op"&gt;.&lt;/span&gt;output&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb21-10"&gt;&lt;a href="#cb21-10" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb21-11"&gt;&lt;a href="#cb21-11" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; arg_idents &lt;span class="op"&gt;=&lt;/span&gt; extract_arg_idents(fn_args&lt;span class="op"&gt;.&lt;/span&gt;clone())&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb21-12"&gt;&lt;a href="#cb21-12" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; first_ident &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="op"&gt;&amp;amp;&lt;/span&gt;arg_idents&lt;span class="op"&gt;.&lt;/span&gt;first()&lt;span class="op"&gt;.&lt;/span&gt;unwrap()&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb21-13"&gt;&lt;a href="#cb21-13" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb21-14"&gt;&lt;a href="#cb21-14" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;  &lt;span class="co"&gt;// remember, our curried body starts with the second argument!&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb21-15"&gt;&lt;a href="#cb21-15" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; curried_body &lt;span class="op"&gt;=&lt;/span&gt; generate_body(&lt;span class="op"&gt;&amp;amp;&lt;/span&gt;arg_idents[&lt;span class="dv"&gt;1&lt;/span&gt;&lt;span class="op"&gt;..&lt;/span&gt;]&lt;span class="op"&gt;,&lt;/span&gt; fn_body&lt;span class="op"&gt;.&lt;/span&gt;clone())&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb21-16"&gt;&lt;a href="#cb21-16" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;  &lt;span class="pp"&gt;println!&lt;/span&gt;(&lt;span class="st"&gt;&amp;quot;{}&amp;quot;&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; curried_body)&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb21-17"&gt;&lt;a href="#cb21-17" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb21-18"&gt;&lt;a href="#cb21-18" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;return&lt;/span&gt; &lt;span class="pp"&gt;TokenStream::&lt;/span&gt;new()&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb21-19"&gt;&lt;a href="#cb21-19" aria-hidden="true"&gt;&lt;/a&gt; &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Add a little test to &lt;code&gt;tests/&lt;/code&gt;:&lt;/p&gt;
&lt;div class="sourceCode" id="cb22"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb22-1"&gt;&lt;a href="#cb22-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// tests/smoke.rs&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb22-2"&gt;&lt;a href="#cb22-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb22-3"&gt;&lt;a href="#cb22-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="at"&gt;#[&lt;/span&gt;&lt;span class="pp"&gt;currying::&lt;/span&gt;curry&lt;span class="at"&gt;]&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb22-4"&gt;&lt;a href="#cb22-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; add(x&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; y&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; z&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb22-5"&gt;&lt;a href="#cb22-5" aria-hidden="true"&gt;&lt;/a&gt;  x &lt;span class="op"&gt;+&lt;/span&gt; y &lt;span class="op"&gt;+&lt;/span&gt; z&lt;/span&gt;
&lt;span id="cb22-6"&gt;&lt;a href="#cb22-6" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb22-7"&gt;&lt;a href="#cb22-7" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb22-8"&gt;&lt;a href="#cb22-8" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="at"&gt;#[&lt;/span&gt;test&lt;span class="at"&gt;]&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb22-9"&gt;&lt;a href="#cb22-9" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; works() &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb22-10"&gt;&lt;a href="#cb22-10" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="pp"&gt;assert!&lt;/span&gt;(&lt;span class="cn"&gt;true&lt;/span&gt;)&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb22-11"&gt;&lt;a href="#cb22-11" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;You should find something like this in the output of &lt;code&gt;cargo test&lt;/code&gt;:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;return move | y | move | z | { x + y + z }&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Glorious &lt;code&gt;println!&lt;/code&gt; debugging!&lt;/p&gt;
&lt;h4 id="function-signature"&gt;Function signature&lt;/h4&gt;
&lt;p&gt;This section gets into the more complicated bits of the macro, generating type aliases and the function signature. By the end of this section, we should have a full working auto-currying macro!&lt;/p&gt;
&lt;p&gt;Recall what our generated type aliases should look like, for our &lt;code&gt;add&lt;/code&gt; function:&lt;/p&gt;
&lt;div class="sourceCode" id="cb24"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb24-1"&gt;&lt;a href="#cb24-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T0 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb24-2"&gt;&lt;a href="#cb24-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T1 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; T0&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb24-3"&gt;&lt;a href="#cb24-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T2 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; T1&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;In general:&lt;/p&gt;
&lt;div class="sourceCode" id="cb25"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb25-1"&gt;&lt;a href="#cb25-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T0 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="op"&gt;&amp;lt;&lt;/span&gt;&lt;span class="kw"&gt;return&lt;/span&gt; &lt;span class="kw"&gt;type&lt;/span&gt;&amp;gt;&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb25-2"&gt;&lt;a href="#cb25-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T1 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;&lt;span class="kw"&gt;type&lt;/span&gt; of arg N&amp;gt;) -&amp;gt; T0&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb25-3"&gt;&lt;a href="#cb25-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T2 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;&lt;span class="kw"&gt;type&lt;/span&gt; of arg N - 1&amp;gt;) -&amp;gt; T1&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb25-4"&gt;&lt;a href="#cb25-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;.&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb25-5"&gt;&lt;a href="#cb25-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;.&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb25-6"&gt;&lt;a href="#cb25-6" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;.&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb25-7"&gt;&lt;a href="#cb25-7" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T(N-1) &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;&lt;span class="kw"&gt;type&lt;/span&gt; of arg 2&amp;gt;) -&amp;gt; T(N-2)&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;To codegen that, we need the types of:&lt;/p&gt;
&lt;ul&gt;
&lt;li&gt;all our inputs (arguments)&lt;/li&gt;
&lt;li&gt;the output (the return type)&lt;/li&gt;
&lt;/ul&gt;
&lt;p&gt;To fetch the types of all our inputs, we can simply reuse the bits we wrote to fetch the names of all our inputs! (doc: &lt;a href="https://docs.rs/syn/1.0.18/syn/enum.Type.html"&gt;Type&lt;/a&gt;)&lt;/p&gt;
&lt;div class="sourceCode" id="cb26"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb26-1"&gt;&lt;a href="#cb26-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// src/lib.rs&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb26-2"&gt;&lt;a href="#cb26-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb26-3"&gt;&lt;a href="#cb26-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;use&lt;/span&gt; &lt;span class="pp"&gt;syn::&lt;/span&gt;&lt;span class="op"&gt;{&lt;/span&gt;parse_macro_input&lt;span class="op"&gt;,&lt;/span&gt; Block&lt;span class="op"&gt;,&lt;/span&gt; FnArg&lt;span class="op"&gt;,&lt;/span&gt; ItemFn&lt;span class="op"&gt;,&lt;/span&gt; Pat&lt;span class="op"&gt;,&lt;/span&gt; ReturnType&lt;span class="op"&gt;,&lt;/span&gt; Type&lt;span class="op"&gt;};&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb26-4"&gt;&lt;a href="#cb26-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb26-5"&gt;&lt;a href="#cb26-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; extract_type(a&lt;span class="op"&gt;:&lt;/span&gt; FnArg) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;Box&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;Type&lt;span class="op"&gt;&amp;gt;&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb26-6"&gt;&lt;a href="#cb26-6" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;match&lt;/span&gt; a &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb26-7"&gt;&lt;a href="#cb26-7" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="pp"&gt;FnArg::&lt;/span&gt;Typed(p) &lt;span class="op"&gt;=&amp;gt;&lt;/span&gt; p&lt;span class="op"&gt;.&lt;/span&gt;ty&lt;span class="op"&gt;,&lt;/span&gt;  &lt;span class="co"&gt;// notice `ty` instead of `pat`&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb26-8"&gt;&lt;a href="#cb26-8" aria-hidden="true"&gt;&lt;/a&gt;      _ &lt;span class="op"&gt;=&amp;gt;&lt;/span&gt; &lt;span class="pp"&gt;panic!&lt;/span&gt;(&lt;span class="st"&gt;&amp;quot;Not supported on types with `self`!&amp;quot;&lt;/span&gt;)&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb26-9"&gt;&lt;a href="#cb26-9" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb26-10"&gt;&lt;a href="#cb26-10" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb26-11"&gt;&lt;a href="#cb26-11" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb26-12"&gt;&lt;a href="#cb26-12" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; extract_arg_types(fn_args&lt;span class="op"&gt;:&lt;/span&gt; Punctuated&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;FnArg&lt;span class="op"&gt;,&lt;/span&gt; &lt;span class="pp"&gt;syn::token::&lt;/span&gt;Comma&lt;span class="op"&gt;&amp;gt;&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;Vec&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;&lt;span class="dt"&gt;Box&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;Type&lt;span class="op"&gt;&amp;gt;&amp;gt;&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb26-13"&gt;&lt;a href="#cb26-13" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;return&lt;/span&gt; fn_args&lt;span class="op"&gt;.&lt;/span&gt;into_iter()&lt;span class="op"&gt;.&lt;/span&gt;map(extract_type)&lt;span class="op"&gt;.&lt;/span&gt;&lt;span class="pp"&gt;collect::&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;&lt;span class="dt"&gt;Vec&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;_&lt;span class="op"&gt;&amp;gt;&amp;gt;&lt;/span&gt;()&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb26-14"&gt;&lt;a href="#cb26-14" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb26-15"&gt;&lt;a href="#cb26-15" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;A good reader would have looked at the docs for output member of the &lt;code&gt;syn::Signature&lt;/code&gt; struct. It has the type &lt;code&gt;syn::ReturnType&lt;/code&gt;. So there is no extraction to do here right? There are actually a couple of things we have to ensure here:&lt;/p&gt;
&lt;ol type="1"&gt;
&lt;li&gt;&lt;p&gt;We need to ensure that the function returns! A function that does not return is pointless in this case, and I will tell you why, in the &lt;a href="#notes"&gt;Notes&lt;/a&gt; section.&lt;/p&gt;&lt;/li&gt;
&lt;li&gt;&lt;p&gt;A &lt;code&gt;ReturnType&lt;/code&gt; encloses the arrow of the return as well, we need to get rid of that. Recall:&lt;/p&gt;
&lt;div class="sourceCode" id="cb27"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb27-1"&gt;&lt;a href="#cb27-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T0 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb27-2"&gt;&lt;a href="#cb27-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// and not&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb27-3"&gt;&lt;a href="#cb27-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T0 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;&lt;/li&gt;
&lt;/ol&gt;
&lt;p&gt;Here is the snippet that handles extraction of the return type (doc: &lt;a href="https://docs.rs/syn/1.0.19/syn/enum.ReturnType.html"&gt;syn::ReturnType&lt;/a&gt;):&lt;/p&gt;
&lt;div class="sourceCode" id="cb28"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb28-1"&gt;&lt;a href="#cb28-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// src/lib.rs&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb28-2"&gt;&lt;a href="#cb28-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb28-3"&gt;&lt;a href="#cb28-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; extract_return_type(a&lt;span class="op"&gt;:&lt;/span&gt; ReturnType) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;Box&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;Type&lt;span class="op"&gt;&amp;gt;&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb28-4"&gt;&lt;a href="#cb28-4" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;match&lt;/span&gt; a &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb28-5"&gt;&lt;a href="#cb28-5" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="pp"&gt;ReturnType::&lt;/span&gt;Type(_&lt;span class="op"&gt;,&lt;/span&gt; p) &lt;span class="op"&gt;=&amp;gt;&lt;/span&gt; p&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb28-6"&gt;&lt;a href="#cb28-6" aria-hidden="true"&gt;&lt;/a&gt;    _ &lt;span class="op"&gt;=&amp;gt;&lt;/span&gt; &lt;span class="pp"&gt;panic!&lt;/span&gt;(&lt;span class="st"&gt;&amp;quot;Not supported on functions without return types!&amp;quot;&lt;/span&gt;)&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb28-7"&gt;&lt;a href="#cb28-7" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb28-8"&gt;&lt;a href="#cb28-8" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;You might notice that we are making extensive use of the &lt;code&gt;panic!&lt;/code&gt; macro. Well, that is because it is a good idea to quit on receiving an unsatisfactory &lt;code&gt;TokenStream&lt;/code&gt;.&lt;/p&gt;
&lt;p&gt;With all our types ready, we can get on with generating type aliases:&lt;/p&gt;
&lt;div class="sourceCode" id="cb29"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb29-1"&gt;&lt;a href="#cb29-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// src/lib.rs&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-2"&gt;&lt;a href="#cb29-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb29-3"&gt;&lt;a href="#cb29-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;use&lt;/span&gt; &lt;span class="pp"&gt;quote::&lt;/span&gt;&lt;span class="op"&gt;{&lt;/span&gt;quote&lt;span class="op"&gt;,&lt;/span&gt; format_ident&lt;span class="op"&gt;};&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-4"&gt;&lt;a href="#cb29-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb29-5"&gt;&lt;a href="#cb29-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; generate_type_aliases(&lt;/span&gt;
&lt;span id="cb29-6"&gt;&lt;a href="#cb29-6" aria-hidden="true"&gt;&lt;/a&gt;  fn_arg_types&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="op"&gt;&amp;amp;&lt;/span&gt;[&lt;span class="dt"&gt;Box&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;Type&lt;span class="op"&gt;&amp;gt;&lt;/span&gt;]&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-7"&gt;&lt;a href="#cb29-7" aria-hidden="true"&gt;&lt;/a&gt;  fn_return_type&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;Box&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;Type&lt;span class="op"&gt;&amp;gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-8"&gt;&lt;a href="#cb29-8" aria-hidden="true"&gt;&lt;/a&gt;  fn_name&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="op"&gt;&amp;amp;&lt;/span&gt;&lt;span class="pp"&gt;syn::&lt;/span&gt;Ident&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-9"&gt;&lt;a href="#cb29-9" aria-hidden="true"&gt;&lt;/a&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;Vec&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;&lt;span class="pp"&gt;proc_macro2::&lt;/span&gt;TokenStream&lt;span class="op"&gt;&amp;gt;&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;    &lt;span class="co"&gt;// 1&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-10"&gt;&lt;a href="#cb29-10" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb29-11"&gt;&lt;a href="#cb29-11" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; type_t0 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="pp"&gt;format_ident!&lt;/span&gt;(&lt;span class="st"&gt;&amp;quot;_{}_T0&amp;quot;&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; fn_name)&lt;span class="op"&gt;;&lt;/span&gt;    &lt;span class="co"&gt;// 2&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-12"&gt;&lt;a href="#cb29-12" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; &lt;span class="kw"&gt;mut&lt;/span&gt; type_aliases &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="pp"&gt;vec!&lt;/span&gt;[&lt;span class="pp"&gt;quote!&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt; &lt;span class="kw"&gt;type&lt;/span&gt; #type_t0 &lt;span class="op"&gt;=&lt;/span&gt; #fn_return_type  &lt;span class="op"&gt;}&lt;/span&gt;]&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-13"&gt;&lt;a href="#cb29-13" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb29-14"&gt;&lt;a href="#cb29-14" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="co"&gt;// 3&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-15"&gt;&lt;a href="#cb29-15" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;for&lt;/span&gt; (i&lt;span class="op"&gt;,&lt;/span&gt; t) &lt;span class="kw"&gt;in&lt;/span&gt; (&lt;span class="dv"&gt;1&lt;/span&gt;&lt;span class="op"&gt;..&lt;/span&gt;)&lt;span class="op"&gt;.&lt;/span&gt;zip(fn_arg_types&lt;span class="op"&gt;.&lt;/span&gt;into_iter()&lt;span class="op"&gt;.&lt;/span&gt;rev()) &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-16"&gt;&lt;a href="#cb29-16" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;let&lt;/span&gt; p &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="pp"&gt;format_ident!&lt;/span&gt;(&lt;span class="st"&gt;&amp;quot;_{}_{}&amp;quot;&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; fn_name&lt;span class="op"&gt;,&lt;/span&gt; &lt;span class="pp"&gt;format!&lt;/span&gt;(&lt;span class="st"&gt;&amp;quot;T{}&amp;quot;&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; i &lt;span class="op"&gt;-&lt;/span&gt; &lt;span class="dv"&gt;1&lt;/span&gt;))&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-17"&gt;&lt;a href="#cb29-17" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;let&lt;/span&gt; n &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="pp"&gt;format_ident!&lt;/span&gt;(&lt;span class="st"&gt;&amp;quot;_{}_{}&amp;quot;&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; fn_name&lt;span class="op"&gt;,&lt;/span&gt; &lt;span class="pp"&gt;format!&lt;/span&gt;(&lt;span class="st"&gt;&amp;quot;T{}&amp;quot;&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; i))&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-18"&gt;&lt;a href="#cb29-18" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb29-19"&gt;&lt;a href="#cb29-19" aria-hidden="true"&gt;&lt;/a&gt;    type_aliases&lt;span class="op"&gt;.&lt;/span&gt;push(&lt;span class="pp"&gt;quote!&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-20"&gt;&lt;a href="#cb29-20" aria-hidden="true"&gt;&lt;/a&gt;        &lt;span class="kw"&gt;type&lt;/span&gt; #n &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(#t) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; #p&lt;/span&gt;
&lt;span id="cb29-21"&gt;&lt;a href="#cb29-21" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="op"&gt;}&lt;/span&gt;)&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-22"&gt;&lt;a href="#cb29-22" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-23"&gt;&lt;a href="#cb29-23" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb29-24"&gt;&lt;a href="#cb29-24" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;return&lt;/span&gt; type_aliases&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb29-25"&gt;&lt;a href="#cb29-25" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;&lt;strong&gt;1. The return value&lt;/strong&gt;&lt;br /&gt;
We are returning a &lt;code&gt;Vec&amp;lt;proc_macro2::TokenStream&amp;gt;&lt;/code&gt;, i. e., a list of &lt;code&gt;TokenStream&lt;/code&gt;s, where each item is a type alias.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;2. Format identifier?&lt;/strong&gt;&lt;br /&gt;
I’ve got some explanation to do on this line. Clearly, we are trying to write the first type alias, and initialize our &lt;code&gt;TokenStream&lt;/code&gt; vector with &lt;code&gt;T0&lt;/code&gt;, because it is different from the others:&lt;/p&gt;
&lt;div class="sourceCode" id="cb30"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb30-1"&gt;&lt;a href="#cb30-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T0 &lt;span class="op"&gt;=&lt;/span&gt; something&lt;/span&gt;
&lt;span id="cb30-2"&gt;&lt;a href="#cb30-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// the others are of the form&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb30-3"&gt;&lt;a href="#cb30-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; Tr &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(something) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; something&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;&lt;code&gt;format_ident!&lt;/code&gt; is similar to &lt;code&gt;format!&lt;/code&gt;. Instead of returning a formatted string, it returns a &lt;code&gt;syn::Ident&lt;/code&gt;. Therefore, &lt;code&gt;type_t0&lt;/code&gt; is actually an identifier for, in the case of our &lt;code&gt;add&lt;/code&gt; function, &lt;code&gt;_add_T0&lt;/code&gt;. Why is this formatting important? Namespacing.&lt;/p&gt;
&lt;p&gt;Picture this, we have two functions, &lt;code&gt;add&lt;/code&gt; and &lt;code&gt;subtract&lt;/code&gt;, that we wish to curry with our macro:&lt;/p&gt;
&lt;div class="sourceCode" id="cb31"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb31-1"&gt;&lt;a href="#cb31-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="at"&gt;#[&lt;/span&gt;curry&lt;span class="at"&gt;]&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb31-2"&gt;&lt;a href="#cb31-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; add(&lt;span class="op"&gt;...&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt; &lt;span class="op"&gt;...&lt;/span&gt; &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb31-3"&gt;&lt;a href="#cb31-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb31-4"&gt;&lt;a href="#cb31-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="at"&gt;#[&lt;/span&gt;curry&lt;span class="at"&gt;]&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb31-5"&gt;&lt;a href="#cb31-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; sub(&lt;span class="op"&gt;...&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt; &lt;span class="op"&gt;...&lt;/span&gt; &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Here is the same but with macros expanded:&lt;/p&gt;
&lt;div class="sourceCode" id="cb32"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb32-1"&gt;&lt;a href="#cb32-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T0 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb32-2"&gt;&lt;a href="#cb32-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T1 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; T0&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb32-3"&gt;&lt;a href="#cb32-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; add( &lt;span class="op"&gt;...&lt;/span&gt; ) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; T1 &lt;span class="op"&gt;{&lt;/span&gt; &lt;span class="op"&gt;...&lt;/span&gt; &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb32-4"&gt;&lt;a href="#cb32-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb32-5"&gt;&lt;a href="#cb32-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T0 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb32-6"&gt;&lt;a href="#cb32-6" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; T1 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; T0&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb32-7"&gt;&lt;a href="#cb32-7" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; sub( &lt;span class="op"&gt;...&lt;/span&gt; ) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; T1 &lt;span class="op"&gt;{&lt;/span&gt; &lt;span class="op"&gt;...&lt;/span&gt; &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;We end up with two definitions of &lt;code&gt;T0&lt;/code&gt;! Now, if we do the little &lt;code&gt;format_ident!&lt;/code&gt; dance we did up there:&lt;/p&gt;
&lt;div class="sourceCode" id="cb33"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb33-1"&gt;&lt;a href="#cb33-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; _add_T0 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb33-2"&gt;&lt;a href="#cb33-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; _add_T1 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; _add_T0&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb33-3"&gt;&lt;a href="#cb33-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; add( &lt;span class="op"&gt;...&lt;/span&gt; ) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; _add_T1 &lt;span class="op"&gt;{&lt;/span&gt; &lt;span class="op"&gt;...&lt;/span&gt; &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb33-4"&gt;&lt;a href="#cb33-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb33-5"&gt;&lt;a href="#cb33-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; _sub_T0 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb33-6"&gt;&lt;a href="#cb33-6" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; _sub_T1 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; _sub_T0&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb33-7"&gt;&lt;a href="#cb33-7" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; sub( &lt;span class="op"&gt;...&lt;/span&gt; ) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; _sub_T1 &lt;span class="op"&gt;{&lt;/span&gt; &lt;span class="op"&gt;...&lt;/span&gt; &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Voilà! The type aliases don’t tread on each other. Remember to import &lt;code&gt;format_ident&lt;/code&gt; from the &lt;code&gt;quote&lt;/code&gt; crate.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;3. The TokenStream Vector&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;We iterate over our types in reverse order (&lt;code&gt;T0&lt;/code&gt; is the last return, &lt;code&gt;T1&lt;/code&gt; is the second last, so on), assign a number to each iteration with &lt;code&gt;zip&lt;/code&gt;, generate type names with &lt;code&gt;format_ident&lt;/code&gt;, push a &lt;code&gt;TokenStream&lt;/code&gt; with the help of &lt;code&gt;quote&lt;/code&gt; and variable interpolation.&lt;/p&gt;
&lt;p&gt;If you are wondering why we used &lt;code&gt;(1..).zip()&lt;/code&gt; instead of &lt;code&gt;.enumerate()&lt;/code&gt;, it’s because we wanted to start counting from 1 instead of 0 (we are already done with &lt;code&gt;T0&lt;/code&gt;!).&lt;/p&gt;
&lt;h4 id="getting-it-together"&gt;Getting it together&lt;/h4&gt;
&lt;p&gt;I promised we’d have a fully working macro by the end of last section. I lied, we have to tie everything together in our &lt;code&gt;generate_curry&lt;/code&gt; function:&lt;/p&gt;
&lt;div class="sourceCode" id="cb34"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb34-1"&gt;&lt;a href="#cb34-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// src/lib.rs&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-2"&gt;&lt;a href="#cb34-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb34-3"&gt;&lt;a href="#cb34-3" aria-hidden="true"&gt;&lt;/a&gt; &lt;span class="kw"&gt;fn&lt;/span&gt; generate_curry(parsed&lt;span class="op"&gt;:&lt;/span&gt; ItemFn) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="pp"&gt;proc_macro2::&lt;/span&gt;TokenStream &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-4"&gt;&lt;a href="#cb34-4" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; fn_body &lt;span class="op"&gt;=&lt;/span&gt; parsed&lt;span class="op"&gt;.&lt;/span&gt;block&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-5"&gt;&lt;a href="#cb34-5" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; sig &lt;span class="op"&gt;=&lt;/span&gt; parsed&lt;span class="op"&gt;.&lt;/span&gt;sig&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-6"&gt;&lt;a href="#cb34-6" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; vis &lt;span class="op"&gt;=&lt;/span&gt; parsed&lt;span class="op"&gt;.&lt;/span&gt;vis&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-7"&gt;&lt;a href="#cb34-7" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; fn_name &lt;span class="op"&gt;=&lt;/span&gt; sig&lt;span class="op"&gt;.&lt;/span&gt;ident&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-8"&gt;&lt;a href="#cb34-8" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; fn_args &lt;span class="op"&gt;=&lt;/span&gt; sig&lt;span class="op"&gt;.&lt;/span&gt;inputs&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-9"&gt;&lt;a href="#cb34-9" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; fn_return_type &lt;span class="op"&gt;=&lt;/span&gt; sig&lt;span class="op"&gt;.&lt;/span&gt;output&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-10"&gt;&lt;a href="#cb34-10" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb34-11"&gt;&lt;a href="#cb34-11" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; arg_idents &lt;span class="op"&gt;=&lt;/span&gt; extract_arg_idents(fn_args&lt;span class="op"&gt;.&lt;/span&gt;clone())&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-12"&gt;&lt;a href="#cb34-12" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; first_ident &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="op"&gt;&amp;amp;&lt;/span&gt;arg_idents&lt;span class="op"&gt;.&lt;/span&gt;first()&lt;span class="op"&gt;.&lt;/span&gt;unwrap()&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-13"&gt;&lt;a href="#cb34-13" aria-hidden="true"&gt;&lt;/a&gt;   &lt;span class="kw"&gt;let&lt;/span&gt; curried_body &lt;span class="op"&gt;=&lt;/span&gt; generate_body(&lt;span class="op"&gt;&amp;amp;&lt;/span&gt;arg_idents[&lt;span class="dv"&gt;1&lt;/span&gt;&lt;span class="op"&gt;..&lt;/span&gt;]&lt;span class="op"&gt;,&lt;/span&gt; fn_body&lt;span class="op"&gt;.&lt;/span&gt;clone())&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-14"&gt;&lt;a href="#cb34-14" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb34-15"&gt;&lt;a href="#cb34-15" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; arg_types &lt;span class="op"&gt;=&lt;/span&gt; extract_arg_types(fn_args&lt;span class="op"&gt;.&lt;/span&gt;clone())&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-16"&gt;&lt;a href="#cb34-16" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; first_type &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="op"&gt;&amp;amp;&lt;/span&gt;arg_types&lt;span class="op"&gt;.&lt;/span&gt;first()&lt;span class="op"&gt;.&lt;/span&gt;unwrap()&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-17"&gt;&lt;a href="#cb34-17" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; type_aliases &lt;span class="op"&gt;=&lt;/span&gt; generate_type_aliases(&lt;/span&gt;
&lt;span id="cb34-18"&gt;&lt;a href="#cb34-18" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;      &lt;span class="op"&gt;&amp;amp;&lt;/span&gt;arg_types[&lt;span class="dv"&gt;1&lt;/span&gt;&lt;span class="op"&gt;..&lt;/span&gt;]&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-19"&gt;&lt;a href="#cb34-19" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;      extract_return_type(fn_return_type)&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-20"&gt;&lt;a href="#cb34-20" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;      &lt;span class="op"&gt;&amp;amp;&lt;/span&gt;fn_name&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-21"&gt;&lt;a href="#cb34-21" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;  )&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-22"&gt;&lt;a href="#cb34-22" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb34-23"&gt;&lt;a href="#cb34-23" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; return_type &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="pp"&gt;format_ident!&lt;/span&gt;(&lt;span class="st"&gt;&amp;quot;_{}_{}&amp;quot;&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; &lt;span class="op"&gt;&amp;amp;&lt;/span&gt;fn_name&lt;span class="op"&gt;,&lt;/span&gt; &lt;span class="pp"&gt;format!&lt;/span&gt;(&lt;span class="st"&gt;&amp;quot;T{}&amp;quot;&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; type_aliases&lt;span class="op"&gt;.&lt;/span&gt;len() &lt;span class="op"&gt;-&lt;/span&gt; &lt;span class="dv"&gt;1&lt;/span&gt;))&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-24"&gt;&lt;a href="#cb34-24" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb34-25"&gt;&lt;a href="#cb34-25" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;  &lt;span class="kw"&gt;return&lt;/span&gt; &lt;span class="pp"&gt;quote!&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-26"&gt;&lt;a href="#cb34-26" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;      #(#type_aliases)&lt;span class="op"&gt;;*&lt;/span&gt; &lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-27"&gt;&lt;a href="#cb34-27" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;      #vis &lt;span class="kw"&gt;fn&lt;/span&gt; #fn_name (#first_ident&lt;span class="op"&gt;:&lt;/span&gt; #first_type) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; #return_type &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-28"&gt;&lt;a href="#cb34-28" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;          #curried_body &lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-29"&gt;&lt;a href="#cb34-29" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;      &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-30"&gt;&lt;a href="#cb34-30" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;+&lt;/span&gt;  &lt;span class="op"&gt;};&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb34-31"&gt;&lt;a href="#cb34-31" aria-hidden="true"&gt;&lt;/a&gt; &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Most of the additions are self explanatory, I’ll go through the return statement with you. We are returning a &lt;code&gt;quote!{ ... }&lt;/code&gt;, so a &lt;code&gt;proc_macro2::TokenStream&lt;/code&gt;. We are iterating through the &lt;code&gt;type_aliases&lt;/code&gt; variable, which you might recall, is a &lt;code&gt;Vec&amp;lt;TokenStream&amp;gt;&lt;/code&gt;. You might notice the sneaky semicolon before the &lt;code&gt;*&lt;/code&gt;. This basically tells &lt;code&gt;quote&lt;/code&gt;, to insert an item, then a semicolon, and then the next one, another semicolon, and so on. The semicolon is a separator. We need to manually insert another semicolon at the end of it all, &lt;code&gt;quote&lt;/code&gt; doesn’t insert a separator at the end of the iteration.&lt;/p&gt;
&lt;p&gt;We retain the visibility and name of our original function. Our curried function takes as args, just the first argument of our original function. The return type of our curried function is actually, the last type alias we create. If you think back to our manually curried &lt;code&gt;add&lt;/code&gt; function, we returned &lt;code&gt;T2&lt;/code&gt;, which was in fact, the last type alias we created.&lt;/p&gt;
&lt;p&gt;I am sure, at this point, you are itching to test this out, but before that, let me introduce you to some good methods of debugging proc-macro code.&lt;/p&gt;
&lt;h3 id="debugging-and-testing"&gt;Debugging and Testing&lt;/h3&gt;
&lt;p&gt;Install &lt;code&gt;cargo-expand&lt;/code&gt; via:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;cargo install cargo-expand&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;&lt;code&gt;cargo-expand&lt;/code&gt; is a neat little tool that expands your macro in places where it is used, and lets you view the generated code! For example:&lt;/p&gt;
&lt;pre class="shell"&gt;&lt;code&gt;# create a bin package hello
$ cargo new hello

# view the expansion of the println! macro
$ cargo expand

#![feature(prelude_import)]
#[prelude_import]
use std::prelude::v1::*;
#[macro_use]
extern crate std;
fn main() {
  {
    ::std::io::_print(::core::fmt::Arguments::new_v1(
        &amp;amp;[&amp;quot;Hello, world!\n&amp;quot;],
        &amp;amp;match () {
            () =&amp;gt; [],
        },
      ));
  };
}&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Writing proc-macros without &lt;code&gt;cargo-expand&lt;/code&gt; is tantamount to driving a vehicle without rear view mirrors! Keep an eye on what is going on behind your back.&lt;/p&gt;
&lt;p&gt;Now, your macro won’t always compile, you might just recieve the bee movie script as an error. &lt;code&gt;cargo-expand&lt;/code&gt; will not work in such cases. I would suggest printing out your variables to inspect them. &lt;code&gt;TokenStream&lt;/code&gt; implements &lt;code&gt;Display&lt;/code&gt; as well as &lt;code&gt;Debug&lt;/code&gt;. We don’t always have to be respectable programmers. Just print it.&lt;/p&gt;
&lt;p&gt;Enough of that, lets get testing:&lt;/p&gt;
&lt;div class="sourceCode" id="cb37"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb37-1"&gt;&lt;a href="#cb37-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// tests/smoke.rs&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb37-2"&gt;&lt;a href="#cb37-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb37-3"&gt;&lt;a href="#cb37-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="at"&gt;#![&lt;/span&gt;feature&lt;span class="at"&gt;(&lt;/span&gt;type_alias_impl_trait&lt;span class="at"&gt;)]&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb37-4"&gt;&lt;a href="#cb37-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb37-5"&gt;&lt;a href="#cb37-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="at"&gt;#[&lt;/span&gt;&lt;span class="pp"&gt;crate_name::&lt;/span&gt;curry&lt;span class="at"&gt;]&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb37-6"&gt;&lt;a href="#cb37-6" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; add(x&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; y&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; z&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb37-7"&gt;&lt;a href="#cb37-7" aria-hidden="true"&gt;&lt;/a&gt;   x &lt;span class="op"&gt;+&lt;/span&gt; y &lt;span class="op"&gt;+&lt;/span&gt; z&lt;/span&gt;
&lt;span id="cb37-8"&gt;&lt;a href="#cb37-8" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb37-9"&gt;&lt;a href="#cb37-9" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb37-10"&gt;&lt;a href="#cb37-10" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="at"&gt;#[&lt;/span&gt;test&lt;span class="at"&gt;]&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb37-11"&gt;&lt;a href="#cb37-11" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; works() &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb37-12"&gt;&lt;a href="#cb37-12" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="pp"&gt;assert_eq!&lt;/span&gt;(&lt;span class="dv"&gt;15&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; add(&lt;span class="dv"&gt;4&lt;/span&gt;)(&lt;span class="dv"&gt;5&lt;/span&gt;)(&lt;span class="dv"&gt;6&lt;/span&gt;))&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb37-13"&gt;&lt;a href="#cb37-13" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Run &lt;code&gt;cargo +nightly test&lt;/code&gt;. You should see a pleasing message:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;running 1 test
test tests::works ... ok&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Take a look at the expansion for our curry macro, via &lt;code&gt;cargo +nightly expand --tests smoke&lt;/code&gt;:&lt;/p&gt;
&lt;div class="sourceCode" id="cb39"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb39-1"&gt;&lt;a href="#cb39-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; _add_T0 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb39-2"&gt;&lt;a href="#cb39-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; _add_T1 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; _add_T0&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb39-3"&gt;&lt;a href="#cb39-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;type&lt;/span&gt; _add_T2 &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="kw"&gt;impl&lt;/span&gt; &lt;span class="bu"&gt;Fn&lt;/span&gt;(&lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; _add_T1&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb39-4"&gt;&lt;a href="#cb39-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; add(x&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; _add_T2 &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb39-5"&gt;&lt;a href="#cb39-5" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;return&lt;/span&gt; (&lt;span class="kw"&gt;move&lt;/span&gt; &lt;span class="op"&gt;|&lt;/span&gt;y&lt;span class="op"&gt;|&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb39-6"&gt;&lt;a href="#cb39-6" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="kw"&gt;move&lt;/span&gt; &lt;span class="op"&gt;|&lt;/span&gt;z&lt;span class="op"&gt;|&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb39-7"&gt;&lt;a href="#cb39-7" aria-hidden="true"&gt;&lt;/a&gt;      &lt;span class="kw"&gt;return&lt;/span&gt; x &lt;span class="op"&gt;+&lt;/span&gt; y &lt;span class="op"&gt;+&lt;/span&gt; z&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb39-8"&gt;&lt;a href="#cb39-8" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb39-9"&gt;&lt;a href="#cb39-9" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="op"&gt;}&lt;/span&gt;)&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb39-10"&gt;&lt;a href="#cb39-10" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb39-11"&gt;&lt;a href="#cb39-11" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb39-12"&gt;&lt;a href="#cb39-12" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;// a bunch of other stuff generated by #[test] and assert_eq!&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;A sight for sore eyes.&lt;/p&gt;
&lt;p&gt;Here is a more complex example that generates ten multiples of the first ten natural numbers:&lt;/p&gt;
&lt;div class="sourceCode" id="cb40"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb40-1"&gt;&lt;a href="#cb40-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="at"&gt;#[&lt;/span&gt;curry&lt;span class="at"&gt;]&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb40-2"&gt;&lt;a href="#cb40-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; product(x&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; y&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt;) &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;u32&lt;/span&gt; &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb40-3"&gt;&lt;a href="#cb40-3" aria-hidden="true"&gt;&lt;/a&gt;  x &lt;span class="op"&gt;*&lt;/span&gt; y&lt;/span&gt;
&lt;span id="cb40-4"&gt;&lt;a href="#cb40-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb40-5"&gt;&lt;a href="#cb40-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb40-6"&gt;&lt;a href="#cb40-6" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;fn&lt;/span&gt; multiples() &lt;span class="op"&gt;-&amp;gt;&lt;/span&gt; &lt;span class="dt"&gt;Vec&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;&lt;span class="dt"&gt;Vec&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;&lt;span class="dt"&gt;u32&lt;/span&gt;&lt;span class="op"&gt;&amp;gt;&amp;gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb40-7"&gt;&lt;a href="#cb40-7" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; v &lt;span class="op"&gt;=&lt;/span&gt; (&lt;span class="dv"&gt;1&lt;/span&gt;&lt;span class="op"&gt;..=&lt;/span&gt;&lt;span class="dv"&gt;10&lt;/span&gt;)&lt;span class="op"&gt;.&lt;/span&gt;map(product)&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb40-8"&gt;&lt;a href="#cb40-8" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;return&lt;/span&gt; (&lt;span class="dv"&gt;1&lt;/span&gt;&lt;span class="op"&gt;..=&lt;/span&gt;&lt;span class="dv"&gt;10&lt;/span&gt;)&lt;/span&gt;
&lt;span id="cb40-9"&gt;&lt;a href="#cb40-9" aria-hidden="true"&gt;&lt;/a&gt;      &lt;span class="op"&gt;.&lt;/span&gt;map(&lt;span class="op"&gt;|&lt;/span&gt;x&lt;span class="op"&gt;|&lt;/span&gt; v&lt;span class="op"&gt;.&lt;/span&gt;clone()&lt;span class="op"&gt;.&lt;/span&gt;map(&lt;span class="op"&gt;|&lt;/span&gt;f&lt;span class="op"&gt;|&lt;/span&gt; f(x))&lt;span class="op"&gt;.&lt;/span&gt;collect())&lt;/span&gt;
&lt;span id="cb40-10"&gt;&lt;a href="#cb40-10" aria-hidden="true"&gt;&lt;/a&gt;      &lt;span class="op"&gt;.&lt;/span&gt;collect()&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb40-11"&gt;&lt;a href="#cb40-11" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;h3 id="notes"&gt;Notes&lt;/h3&gt;
&lt;p&gt;I didn’t quite explain why we use &lt;code&gt;move |arg|&lt;/code&gt; in our closure. This is because we want to take ownership of the variable supplied to us. Take a look at this example:&lt;/p&gt;
&lt;div class="sourceCode" id="cb41"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb41-1"&gt;&lt;a href="#cb41-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;let&lt;/span&gt; v &lt;span class="op"&gt;=&lt;/span&gt; add(&lt;span class="dv"&gt;5&lt;/span&gt;)&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb41-2"&gt;&lt;a href="#cb41-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;let&lt;/span&gt; g&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb41-3"&gt;&lt;a href="#cb41-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb41-4"&gt;&lt;a href="#cb41-4" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;let&lt;/span&gt; x &lt;span class="op"&gt;=&lt;/span&gt; &lt;span class="dv"&gt;5&lt;/span&gt;&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb41-5"&gt;&lt;a href="#cb41-5" aria-hidden="true"&gt;&lt;/a&gt;  g &lt;span class="op"&gt;=&lt;/span&gt; v(x)&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb41-6"&gt;&lt;a href="#cb41-6" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb41-7"&gt;&lt;a href="#cb41-7" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="pp"&gt;println!&lt;/span&gt;(&lt;span class="st"&gt;&amp;quot;{}&amp;quot;&lt;/span&gt;&lt;span class="op"&gt;,&lt;/span&gt; g(&lt;span class="dv"&gt;2&lt;/span&gt;))&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Variable &lt;code&gt;x&lt;/code&gt; goes out of scope before &lt;code&gt;g&lt;/code&gt; can return a concrete value. If we take ownership of &lt;code&gt;x&lt;/code&gt; by &lt;code&gt;move&lt;/code&gt;ing it into our closure, we can expect this to work reliably. In fact, rustc understands this, and forces you to use &lt;code&gt;move&lt;/code&gt;.&lt;/p&gt;
&lt;p&gt;This usage of &lt;code&gt;move&lt;/code&gt; is exactly why &lt;strong&gt;a curried function without a return is useless&lt;/strong&gt;. Every variable we pass to our curried function gets moved into its local scope. Playing with these variables cannot cause a change outside this scope. Returning is our only method of interaction with anything beyond this function.&lt;/p&gt;
&lt;h3 id="conclusion"&gt;Conclusion&lt;/h3&gt;
&lt;p&gt;Currying may not seem to be all that useful. Curried functions are unwieldy in Rust because the standard library is not built around currying. If you enjoy the possibilities posed by currying, consider taking a look at Haskell or Scheme.&lt;/p&gt;
&lt;p&gt;My original intention with &lt;a href="https://peppe.rs"&gt;peppe.rs&lt;/a&gt; was to post condensed articles, a micro blog, but this one turned out extra long.&lt;/p&gt;
&lt;p&gt;Perhaps I should call it a ‘macro’ blog :)&lt;/p&gt;
&lt;section class="footnotes" role="doc-endnotes"&gt;
&lt;hr /&gt;
&lt;ol&gt;
&lt;li id="fn1" role="doc-endnote"&gt;&lt;p&gt;&lt;a href="https://doc.rust-lang.org/book/ch13-01-closures.html"&gt;https://doc.rust-lang.org/book/ch13-01-closures.html&lt;/a&gt;&lt;a href="#fnref1" class="footnote-back" role="doc-backlink"&gt;↩︎&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;
&lt;li id="fn2" role="doc-endnote"&gt;&lt;p&gt;&lt;a href="https://caniuse.rs"&gt;caniuse.rs&lt;/a&gt; contains an indexed list of features and their status.&lt;a href="#fnref2" class="footnote-back" role="doc-backlink"&gt;↩︎&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;
&lt;/ol&gt;
&lt;/section&gt;</description>
<link>https://peppe.rs/posts/auto-currying_rust_functions/</link>
<pubDate>Fri, 08 May 2020 18:30:00 +0000</pubDate>
<guid>https://peppe.rs/posts/auto-currying_rust_functions/</guid>
</item>
<item>
<title>Pixel Art In GIMP</title>
<description>&lt;p&gt;I’ve always been an admirer of pixel art, because of it’s simplicity and it’s resemblance to bitmap font design. Recently, I decided to take the dive and make some art of my own.&lt;/p&gt;
&lt;p&gt;I used GIMP because I am fairly familiar with it. Aseprite seems to be the editor of choice for animated pixel art though.&lt;/p&gt;
&lt;h3 id="setting-up-the-canvas"&gt;Setting up the canvas&lt;/h3&gt;
&lt;p&gt;Picking a canvas size is daunting. Too small, and you won’t be able to fit in enough detail to make a legible piece. Too big and you’ve got too many pixels to work with!&lt;/p&gt;
&lt;p&gt;I would suggest starting out with anywhere between 100x100 and 200x200. &lt;a href="https://u.peppe.rs/u9.png"&gt;Here’s&lt;/a&gt; a sample configuration.&lt;/p&gt;
&lt;p&gt;Sometimes I use a 10x10 grid, &lt;code&gt;View &amp;gt; Show Grid&lt;/code&gt; and &lt;code&gt;Edit &amp;gt; Preferences &amp;gt; Default Grid &amp;gt; Spacing&lt;/code&gt;, but that can get jarring, so I throw down a couple of guides, drag right or down from the left or top gutters for vertical and horizontal guides respectively.&lt;/p&gt;
&lt;h3 id="choosing-a-brush"&gt;Choosing a Brush&lt;/h3&gt;
&lt;p&gt;The most important part of our setup is the brush. Use the Pencil Tool (&lt;code&gt;n&lt;/code&gt; on the keyboard) for hard edge drawings. Here’s a small comparison if you don’t know the difference between a hard edge and a soft edge:&lt;/p&gt;
&lt;figure&gt;
&lt;img src="https://u.peppe.rs/kz.png" alt="Hard edge vs Soft Edge" /&gt;&lt;figcaption aria-hidden="true"&gt;Hard edge vs Soft Edge&lt;/figcaption&gt;
&lt;/figure&gt;
&lt;p&gt;I turn the size down all the way to 1 (&lt;code&gt;[&lt;/code&gt; on the keyboard). Set &lt;code&gt;Dynamics&lt;/code&gt; off. &lt;a href="https://u.peppe.rs/Fs.png"&gt;Here’s&lt;/a&gt; a sample brush configuration.&lt;/p&gt;
&lt;h3 id="laying-down-the-pixels"&gt;Laying down the pixels!&lt;/h3&gt;
&lt;p&gt;With the boring stuff out of the way, we can start with our piece. I usually follow a three step process:&lt;/p&gt;
&lt;ul&gt;
&lt;li&gt;draw a rough outline&lt;/li&gt;
&lt;li&gt;fill in the shadows&lt;/li&gt;
&lt;li&gt;add highlights&lt;/li&gt;
&lt;/ul&gt;
&lt;p&gt;But this process is better explained with an example: an onigiri. Let us start off with a 100x100 canvas.&lt;/p&gt;
&lt;h4 id="drawing-the-outline"&gt;Drawing the outline&lt;/h4&gt;
&lt;p&gt;For the most part, our figure will be symmetric. If you are on GIMP 2.10+, you can take advantage of the Symmetry Painting feature. Go ahead and enable vertical symmetry, &lt;code&gt;Window &amp;gt; Dockable Dialogs &amp;gt; Symmetry Painting&lt;/code&gt; and &lt;code&gt;Symmetry Painting &amp;gt; Symmetry &amp;gt; Mirror &amp;gt; Vertical&lt;/code&gt;.&lt;/p&gt;
&lt;p&gt;If you are running an older version of GIMP, draw in the left side, duplicate the layer, flip it horizontally, and merge it with the original.&lt;/p&gt;
&lt;p&gt;Your outline might look something like this:&lt;/p&gt;
&lt;p&gt;&lt;img src="https://u.peppe.rs/mn.png" /&gt;&lt;/p&gt;
&lt;p&gt;Go ahead and fill it in with the fill tool (&lt;code&gt;Shift + b&lt;/code&gt; on the keyboard), add in some seaweed as well, preferably on a different layer. You can toggle symmetry on and off to save yourself some time.&lt;/p&gt;
&lt;p&gt;&lt;img src="https://u.peppe.rs/xu.png" /&gt;&lt;/p&gt;
&lt;h4 id="shadows"&gt;Shadows&lt;/h4&gt;
&lt;p&gt;For now, let us focus on the shadows on the object itself, we’ll come back to the shadows cast by the object on the surface later.&lt;/p&gt;
&lt;p&gt;Shadows on any surface always follow the shape of the surface. A spherical onigiri would have a circular shadow:&lt;/p&gt;
&lt;p&gt;&lt;img src="https://u.peppe.rs/FU.png" /&gt;&lt;/p&gt;
&lt;p&gt;A couple of noticeable changes:&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Layers&lt;/strong&gt;: The layer containing the seaweed has been hidden.&lt;br /&gt;
&lt;strong&gt;Color&lt;/strong&gt;: The color of the shadow is just a slightly lighter version of the original object (reduce the Value on the HSV scale).&lt;br /&gt;
&lt;strong&gt;Area&lt;/strong&gt;: The shadow does not go all the way (notice the bottom edges).&lt;/p&gt;
&lt;p&gt;The shadow does not go all the way because we will be filling in that area with another, darker shadow! An image might explain better:&lt;/p&gt;
&lt;p&gt;&lt;img src="https://u.peppe.rs/Br.png" /&gt;&lt;/p&gt;
&lt;p&gt;To emulate soft lights, reduce the value by 2 to 3 points every iteration. Notice how area &lt;code&gt;1&lt;/code&gt; is much larger than area &lt;code&gt;4&lt;/code&gt;. This is because an onigiri resembles a bottom heavy oblate spheroid, a sphere that is slightly fatter around the lower bottom, and areas &lt;code&gt;1&lt;/code&gt; and &lt;code&gt;2&lt;/code&gt; catch more light than areas &lt;code&gt;3&lt;/code&gt; and &lt;code&gt;4&lt;/code&gt;.&lt;/p&gt;
&lt;p&gt;Do the same with the seaweed. The seaweed, being a smaller, flatter object, doesn’t cast much of a shadow, so stop with 1 or 2 iterations of the gradient:&lt;/p&gt;
&lt;p&gt;&lt;img src="https://u.peppe.rs/T3.png" /&gt;&lt;/p&gt;
&lt;p&gt;We’re getting there!&lt;/p&gt;
&lt;h4 id="highlights"&gt;Highlights&lt;/h4&gt;
&lt;p&gt;This step handles the details on the strongly illuminated portions of the object. Seaweed is a bit glossy, lighten the edges to make it seem shiny. The rice is not as shiny, but it does form an uneven surface. Add in some shadows to promote the idea of rice grains. Here is the finished result:&lt;/p&gt;
&lt;p&gt;&lt;img src="https://u.peppe.rs/VE.png" /&gt;&lt;/p&gt;
&lt;h3 id="finishing-touches"&gt;Finishing Touches&lt;/h3&gt;
&lt;p&gt;Some color correction and &lt;code&gt;a e s t h e t i c&lt;/code&gt; Japanese text later, our piece is complete!&lt;/p&gt;
&lt;p&gt;&lt;img src="https://u.peppe.rs/cn.png" /&gt;&lt;/p&gt;
&lt;p&gt;Hold on, why is it so tiny? Well, that’s because our canvas was 100x100, head over to &lt;code&gt;Image &amp;gt; Scale Image&lt;/code&gt;, set &lt;code&gt;Quality &amp;gt; Interpolation&lt;/code&gt; to &lt;code&gt;None&lt;/code&gt; and scale it up to 700x700, et voilà!&lt;/p&gt;
&lt;p&gt;&lt;img src="https://u.peppe.rs/CH.png" /&gt;&lt;/p&gt;</description>
<link>https://peppe.rs/posts/pixel_art_in_GIMP/</link>
<pubDate>Wed, 08 Apr 2020 18:30:00 +0000</pubDate>
<guid>https://peppe.rs/posts/pixel_art_in_GIMP/</guid>
</item>
<item>
<title>Rapid Refactoring With Vim</title>
<description>&lt;p&gt;Last weekend, I was tasked with refactoring the 96 unit tests on &lt;a href="https://github.com/ruma/ruma-events/pull/70"&gt;ruma-events&lt;/a&gt; to use strictly typed json objects using &lt;code&gt;serde_json::json!&lt;/code&gt; instead of raw strings. It was rather painless thanks to vim :)&lt;/p&gt;
&lt;p&gt;Here’s a small sample of what had to be done (note the lines prefixed with the arrow):&lt;/p&gt;
&lt;div class="sourceCode" id="cb1"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb1-1"&gt;&lt;a href="#cb1-1" aria-hidden="true"&gt;&lt;/a&gt;→ &lt;span class="kw"&gt;use&lt;/span&gt; &lt;span class="pp"&gt;serde_json::&lt;/span&gt;&lt;span class="op"&gt;{&lt;/span&gt;from_str&lt;span class="op"&gt;};&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-2"&gt;&lt;a href="#cb1-2" aria-hidden="true"&gt;&lt;/a&gt;  &lt;/span&gt;
&lt;span id="cb1-3"&gt;&lt;a href="#cb1-3" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="at"&gt;#[&lt;/span&gt;test&lt;span class="at"&gt;]&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-4"&gt;&lt;a href="#cb1-4" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;fn&lt;/span&gt; deserialize() &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-5"&gt;&lt;a href="#cb1-5" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="pp"&gt;assert_eq!&lt;/span&gt;(&lt;/span&gt;
&lt;span id="cb1-6"&gt;&lt;a href="#cb1-6" aria-hidden="true"&gt;&lt;/a&gt;→       &lt;span class="pp"&gt;from_str::&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;Action&lt;span class="op"&gt;&amp;gt;&lt;/span&gt;(&lt;span class="st"&gt;r#&amp;quot;{&amp;quot;set_tweak&amp;quot;: &amp;quot;highlight&amp;quot;}&amp;quot;#&lt;/span&gt;)&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-7"&gt;&lt;a href="#cb1-7" aria-hidden="true"&gt;&lt;/a&gt;        &lt;span class="pp"&gt;Action::&lt;/span&gt;SetTweak(&lt;span class="pp"&gt;Tweak::&lt;/span&gt;Highlight &lt;span class="op"&gt;{&lt;/span&gt; value&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="cn"&gt;true&lt;/span&gt; &lt;span class="op"&gt;}&lt;/span&gt;)&lt;/span&gt;
&lt;span id="cb1-8"&gt;&lt;a href="#cb1-8" aria-hidden="true"&gt;&lt;/a&gt;        )&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-9"&gt;&lt;a href="#cb1-9" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;had to be converted to:&lt;/p&gt;
&lt;div class="sourceCode" id="cb2"&gt;&lt;pre class="sourceCode rust"&gt;&lt;code class="sourceCode rust"&gt;&lt;span id="cb2-1"&gt;&lt;a href="#cb2-1" aria-hidden="true"&gt;&lt;/a&gt;→ &lt;span class="kw"&gt;use&lt;/span&gt; &lt;span class="pp"&gt;serde_json::&lt;/span&gt;&lt;span class="op"&gt;{&lt;/span&gt;from_value&lt;span class="op"&gt;};&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-2"&gt;&lt;a href="#cb2-2" aria-hidden="true"&gt;&lt;/a&gt;  &lt;/span&gt;
&lt;span id="cb2-3"&gt;&lt;a href="#cb2-3" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="at"&gt;#[&lt;/span&gt;test&lt;span class="at"&gt;]&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-4"&gt;&lt;a href="#cb2-4" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="kw"&gt;fn&lt;/span&gt; deserialize() &lt;span class="op"&gt;{&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-5"&gt;&lt;a href="#cb2-5" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="pp"&gt;assert_eq!&lt;/span&gt;(&lt;/span&gt;
&lt;span id="cb2-6"&gt;&lt;a href="#cb2-6" aria-hidden="true"&gt;&lt;/a&gt;→       &lt;span class="pp"&gt;from_value::&lt;/span&gt;&lt;span class="op"&gt;&amp;lt;&lt;/span&gt;Action&lt;span class="op"&gt;&amp;gt;&lt;/span&gt;(&lt;span class="pp"&gt;json!&lt;/span&gt;(&lt;span class="op"&gt;{&lt;/span&gt;&lt;span class="st"&gt;&amp;quot;set_tweak&amp;quot;&lt;/span&gt;&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="st"&gt;&amp;quot;highlight&amp;quot;&lt;/span&gt;&lt;span class="op"&gt;}&lt;/span&gt;))&lt;span class="op"&gt;,&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-7"&gt;&lt;a href="#cb2-7" aria-hidden="true"&gt;&lt;/a&gt;        &lt;span class="pp"&gt;Action::&lt;/span&gt;SetTweak(&lt;span class="pp"&gt;Tweak::&lt;/span&gt;Highlight &lt;span class="op"&gt;{&lt;/span&gt; value&lt;span class="op"&gt;:&lt;/span&gt; &lt;span class="cn"&gt;true&lt;/span&gt; &lt;span class="op"&gt;}&lt;/span&gt;)&lt;/span&gt;
&lt;span id="cb2-8"&gt;&lt;a href="#cb2-8" aria-hidden="true"&gt;&lt;/a&gt;        )&lt;span class="op"&gt;;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-9"&gt;&lt;a href="#cb2-9" aria-hidden="true"&gt;&lt;/a&gt;  &lt;span class="op"&gt;}&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;h3 id="the-arglist"&gt;The arglist&lt;/h3&gt;
&lt;p&gt;For the initial pass, I decided to handle imports, this was a simple find and replace operation, done to all the files containing tests. Luckily, modules (and therefore files) containing tests in Rust are annotated with the &lt;code&gt;#[cfg(test)]&lt;/code&gt; attribute. I opened all such files:&lt;/p&gt;
&lt;div class="sourceCode" id="cb3"&gt;&lt;pre class="sourceCode bash"&gt;&lt;code class="sourceCode bash"&gt;&lt;span id="cb3-1"&gt;&lt;a href="#cb3-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;# `grep -l pattern files` lists all the files&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb3-2"&gt;&lt;a href="#cb3-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;#  matching the pattern&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb3-3"&gt;&lt;a href="#cb3-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb3-4"&gt;&lt;a href="#cb3-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="ex"&gt;vim&lt;/span&gt; &lt;span class="va"&gt;$(&lt;/span&gt;&lt;span class="fu"&gt;grep&lt;/span&gt; -l &lt;span class="st"&gt;&amp;#39;cfg\(test\)&amp;#39;&lt;/span&gt; ./**/*.rs&lt;span class="va"&gt;)&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb3-5"&gt;&lt;a href="#cb3-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb3-6"&gt;&lt;a href="#cb3-6" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;# expands to something like:&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb3-7"&gt;&lt;a href="#cb3-7" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="ex"&gt;vim&lt;/span&gt; push_rules.rs room/member.rs key/verification/lib.rs&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Starting vim with more than one file at the shell prompt populates the arglist. Hit &lt;code&gt;:args&lt;/code&gt; to see the list of files currently ready to edit. The square [brackets] indicate the current file. Navigate through the arglist with &lt;code&gt;:next&lt;/code&gt; and &lt;code&gt;:prev&lt;/code&gt;. I use tpope’s vim-unimpaired &lt;a href="#fn1" class="footnote-ref" id="fnref1" role="doc-noteref"&gt;&lt;sup&gt;1&lt;/sup&gt;&lt;/a&gt;, which adds &lt;code&gt;]a&lt;/code&gt; and &lt;code&gt;[a&lt;/code&gt;, mapped to &lt;code&gt;:next&lt;/code&gt; and &lt;code&gt;:prev&lt;/code&gt;.&lt;/p&gt;
&lt;p&gt;All that’s left to do is the find and replace, for which we will be using vim’s &lt;code&gt;argdo&lt;/code&gt;, applying a substitution to every file in the arglist:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;:argdo s/from_str/from_value/g&lt;/code&gt;&lt;/pre&gt;
&lt;h3 id="the-quickfix-list"&gt;The quickfix list&lt;/h3&gt;
&lt;p&gt;Next up, replacing &lt;code&gt;r#" ... "#&lt;/code&gt; with &lt;code&gt;json!( ... )&lt;/code&gt;. I couldn’t search and replace that trivially, so I went with a macro call &lt;a href="#fn2" class="footnote-ref" id="fnref2" role="doc-noteref"&gt;&lt;sup&gt;2&lt;/sup&gt;&lt;/a&gt; instead, starting with the cursor on ‘r’, represented by the caret, in my attempt to breakdown the process:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;BUFFER:    r#&amp;quot; ... &amp;quot;#;
           ^

ACTION:    vllsjson!(

BUFFER     json!( ... &amp;quot;#;
                ^

ACTION:    &amp;lt;esc&amp;gt;$F#

BUFFER:    json!( ... &amp;quot;#;
                       ^

ACTION:    vhs)&amp;lt;esc&amp;gt;

BUFFER:    json!( ... );&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Here’s the recorded &lt;a href="#fn3" class="footnote-ref" id="fnref3" role="doc-noteref"&gt;&lt;sup&gt;3&lt;/sup&gt;&lt;/a&gt; macro in all its glory: &lt;code&gt;vllsjson!(&amp;lt;esc&amp;gt;$F#vhs)&amp;lt;esc&amp;gt;&lt;/code&gt;.&lt;/p&gt;
&lt;p&gt;Great! So now we just go ahead, find every occurrence of &lt;code&gt;r#&lt;/code&gt; and apply the macro right? Unfortunately, there were more than a few occurrences of raw strings that had to stay raw strings. Enter, the quickfix list.&lt;/p&gt;
&lt;p&gt;The idea behind the quickfix list is to jump from one position in a file to another (maybe in a different file), much like how the arglist lets you jump from one file to another.&lt;/p&gt;
&lt;p&gt;One of the easiest ways to populate this list with a bunch of positions is to use &lt;code&gt;vimgrep&lt;/code&gt;:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;# basic usage
:vimgrep pattern files

# search for raw strings
:vimgrep &amp;#39;r#&amp;#39; ./**/*.rs&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Like &lt;code&gt;:next&lt;/code&gt; and &lt;code&gt;:prev&lt;/code&gt;, you can navigate the quickfix list with &lt;code&gt;:cnext&lt;/code&gt; and &lt;code&gt;:cprev&lt;/code&gt;. Every time you move up or down the list, vim indicates your index:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;(1 of 131): r#&amp;quot;{&amp;quot;set_tweak&amp;quot;: &amp;quot;highlight&amp;quot;}&amp;quot;#;&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;And just like &lt;code&gt;argdo&lt;/code&gt;, you can &lt;code&gt;cdo&lt;/code&gt; to apply commands to &lt;em&gt;every&lt;/em&gt; match in the quickfix list:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;:cdo norm! @q&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;But, I had to manually pick out matches, and it involved some button mashing.&lt;/p&gt;
&lt;h3 id="external-filtering"&gt;External Filtering&lt;/h3&gt;
&lt;p&gt;Some code reviews later, I was asked to format all the json inside the &lt;code&gt;json!&lt;/code&gt; macro. All you have to do is pass a visual selection through a pretty json printer. Select the range to be formatted in visual mode, and hit &lt;code&gt;:&lt;/code&gt;, you will notice the command line displaying what seems to be gibberish:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;:&amp;#39;&amp;lt;,&amp;#39;&amp;gt;&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;&lt;code&gt;'&amp;lt;&lt;/code&gt; and &lt;code&gt;'&amp;gt;&lt;/code&gt; are &lt;em&gt;marks&lt;/em&gt; &lt;a href="#fn4" class="footnote-ref" id="fnref4" role="doc-noteref"&gt;&lt;sup&gt;4&lt;/sup&gt;&lt;/a&gt;. More specifically, they are marks that vim sets automatically every time you make a visual selection, denoting the start and end of the selection.&lt;/p&gt;
&lt;p&gt;A range is one or more line specifiers separated by a &lt;code&gt;,&lt;/code&gt;:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;:1,7       lines 1 through 7
:32        just line 32
:.         the current line
:.,$       the current line to the last line
:&amp;#39;a,&amp;#39;b     mark &amp;#39;a&amp;#39; to mark &amp;#39;b&amp;#39;&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Most &lt;code&gt;:&lt;/code&gt; commands can be prefixed by ranges. &lt;code&gt;:help usr_10.txt&lt;/code&gt; for more on that.&lt;/p&gt;
&lt;p&gt;Alright, lets pass json through &lt;code&gt;python -m json.tool&lt;/code&gt;, a json formatter that accepts &lt;code&gt;stdin&lt;/code&gt; (note the use of &lt;code&gt;!&lt;/code&gt; to make use of an external program):&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;:&amp;#39;&amp;lt;,&amp;#39;&amp;gt;!python -m json.tool&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Unfortunately that didn’t quite work for me because the range included some non-json text as well, a mix of regex and macros helped fix that. I think you get the drift.&lt;/p&gt;
&lt;p&gt;Another fun filter I use from time to time is &lt;code&gt;:!sort&lt;/code&gt;, to sort css attributes, or &lt;code&gt;:!uniq&lt;/code&gt; to remove repeated imports.&lt;/p&gt;
&lt;section class="footnotes" role="doc-endnotes"&gt;
&lt;hr /&gt;
&lt;ol&gt;
&lt;li id="fn1" role="doc-endnote"&gt;&lt;p&gt;https://github.com/tpope/vim-unimpaired It also handles various other mappings, &lt;code&gt;]q&lt;/code&gt; and &lt;code&gt;[q&lt;/code&gt; to navigate the quickfix list for example&lt;a href="#fnref1" class="footnote-back" role="doc-backlink"&gt;↩︎&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;
&lt;li id="fn2" role="doc-endnote"&gt;&lt;p&gt;&lt;code&gt;:help recording&lt;/code&gt;&lt;a href="#fnref2" class="footnote-back" role="doc-backlink"&gt;↩︎&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;
&lt;li id="fn3" role="doc-endnote"&gt;&lt;p&gt;When I’m recording a macro, I prefer starting out by storing it in register &lt;code&gt;q&lt;/code&gt;, and then copying it over to another register if it works as intended. I think of &lt;code&gt;qq&lt;/code&gt; as ‘quick record’.&lt;a href="#fnref3" class="footnote-back" role="doc-backlink"&gt;↩︎&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;
&lt;li id="fn4" role="doc-endnote"&gt;&lt;p&gt;&lt;code&gt;:help mark-motions&lt;/code&gt;&lt;a href="#fnref4" class="footnote-back" role="doc-backlink"&gt;↩︎&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;
&lt;/ol&gt;
&lt;/section&gt;</description>
<link>https://peppe.rs/posts/rapid_refactoring_with_vim/</link>
<pubDate>Tue, 31 Mar 2020 18:30:00 +0000</pubDate>
<guid>https://peppe.rs/posts/rapid_refactoring_with_vim/</guid>
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<item>
<title>Font Size Fallacies</title>
<description>&lt;p&gt;I am not an expert with fonts, but I do have some experience &lt;a href="#fn1" class="footnote-ref" id="fnref1" role="doc-noteref"&gt;&lt;sup&gt;1&lt;/sup&gt;&lt;/a&gt;, and common sense. This post aims to debunk some misconceptions about font sizes!&lt;/p&gt;
&lt;p&gt;11 px on your display is &lt;em&gt;probably not&lt;/em&gt; 11 px on my display. Let’s do some quick math. I have two displays, 1366x768 @ 21" and another with 1920x1080 @ 13", call them &lt;code&gt;A&lt;/code&gt; and &lt;code&gt;B&lt;/code&gt; for now.&lt;/p&gt;
&lt;p&gt;Display &lt;code&gt;A&lt;/code&gt; has 1,049,088 pixels. A pixel is a square, of side say, &lt;code&gt;s&lt;/code&gt; cm. The total area covered by my 21" display is about 1,066 cm^2 (41x26). Thus,&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;Display A
Dimensions: 1366x768 @ 21&amp;quot; (41x26 sq. cm)
1,049,088 s^2 = 1066
            s = 0.0318 cm (side of a pixel on Display A)&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Bear with me, as I repeat the number crunching for Display &lt;code&gt;B&lt;/code&gt;:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;Display B
Dimensions: 1920x1080 @ 13&amp;quot; (29.5x16.5 sq. cm)
2,073,600 s^2 = 486.75
            s = 0.0153 cm (side of a pixel on Display B)&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;The width of a pixel on Display &lt;code&gt;A&lt;/code&gt; is &lt;em&gt;double&lt;/em&gt; the width of a pixel on Display &lt;code&gt;B&lt;/code&gt;. The area occupied by a pixel on Display &lt;code&gt;A&lt;/code&gt; is &lt;em&gt;4 times&lt;/em&gt; the area occupied by a pixel on Display &lt;code&gt;B&lt;/code&gt;.&lt;/p&gt;
&lt;p&gt;&lt;em&gt;The size of a pixel varies from display to display!&lt;/em&gt;&lt;/p&gt;
&lt;p&gt;A 5x11 bitmap font on Display &lt;code&gt;A&lt;/code&gt; would be around 4 mm tall whereas the same bitmap font on Display &lt;code&gt;B&lt;/code&gt; would be around 1.9 mm tall. A 11 px tall character on &lt;code&gt;B&lt;/code&gt; is visually equivalent to a 5 px character on &lt;code&gt;A&lt;/code&gt;. When you view a screenshot of Display &lt;code&gt;A&lt;/code&gt; on Display &lt;code&gt;B&lt;/code&gt;, the contents are shrunk down by a factor of 2!&lt;/p&gt;
&lt;p&gt;So screen resolution is not enough, how else do we measure size? Pixel Density! Keen readers will realize that the 5^th grade math problem we solved up there showcases pixel density, or, pixels per cm (PPCM). Usually we deal with pixels per inch (PPI).&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Note:&lt;/strong&gt; PPI is not to be confused with DPI &lt;a href="#fn2" class="footnote-ref" id="fnref2" role="doc-noteref"&gt;&lt;sup&gt;2&lt;/sup&gt;&lt;/a&gt; (dots per inch). DPI is defined for printers.&lt;/p&gt;
&lt;p&gt;In our example, &lt;code&gt;A&lt;/code&gt; is a 75 ppi display and &lt;code&gt;B&lt;/code&gt; is around 165 ppi &lt;a href="#fn3" class="footnote-ref" id="fnref3" role="doc-noteref"&gt;&lt;sup&gt;3&lt;/sup&gt;&lt;/a&gt;. A low ppi display appears to be ‘pixelated’, because the pixels are more prominent, much like Display &lt;code&gt;A&lt;/code&gt;. A higher ppi usually means you can view larger images and render crispier fonts. The average desktop display can stuff 100-200 pixels per inch. Smart phones usually fall into the 400-600 ppi (XXXHDPI) category. The human eye fails to differentiate detail past 300 ppi.&lt;/p&gt;
&lt;p&gt;&lt;em&gt;So … streaming an 8K video on a 60" TV provides the same clarity as a HD video on a smart phone?&lt;/em&gt;&lt;/p&gt;
&lt;p&gt;Absolutely. Well, clarity is subjective, but the amount of detail you can discern on mobile displays has always been limited. Salty consumers of the Xperia 1 &lt;a href="#fn4" class="footnote-ref" id="fnref4" role="doc-noteref"&gt;&lt;sup&gt;4&lt;/sup&gt;&lt;/a&gt; will say otherwise.&lt;/p&gt;
&lt;p&gt;Maybe I will talk about font rendering in another post, but thats all for now. Don’t judge a font size by its screenshot.&lt;/p&gt;
&lt;section class="footnotes" role="doc-endnotes"&gt;
&lt;hr /&gt;
&lt;ol&gt;
&lt;li id="fn1" role="doc-endnote"&gt;&lt;p&gt;https://github.com/nerdypepper/scientifica&lt;a href="#fnref1" class="footnote-back" role="doc-backlink"&gt;↩︎&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;
&lt;li id="fn2" role="doc-endnote"&gt;&lt;p&gt;https://en.wikipedia.org/wiki/Dots_per_inch&lt;a href="#fnref2" class="footnote-back" role="doc-backlink"&gt;↩︎&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;
&lt;li id="fn3" role="doc-endnote"&gt;&lt;p&gt;https://www.sven.de/dpi/&lt;a href="#fnref3" class="footnote-back" role="doc-backlink"&gt;↩︎&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;
&lt;li id="fn4" role="doc-endnote"&gt;&lt;p&gt;https://en.wikipedia.org/wiki/Sony_Xperia_1&lt;a href="#fnref4" class="footnote-back" role="doc-backlink"&gt;↩︎&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;
&lt;/ol&gt;
&lt;/section&gt;</description>
<link>https://peppe.rs/posts/font_size_fallacies/</link>
<pubDate>Mon, 16 Mar 2020 18:30:00 +0000</pubDate>
<guid>https://peppe.rs/posts/font_size_fallacies/</guid>
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<item>
<title>Termux Tandem</title>
<description>&lt;p&gt;I learnt about &lt;code&gt;termux&lt;/code&gt; from a friend on IRC recently. It looked super gimmicky to me at first, but it eventually proved to be useful. Here’s what I use it for:&lt;/p&gt;
&lt;h3 id="rsync"&gt;rsync&lt;/h3&gt;
&lt;p&gt;Ever since I degoogled my android device, syncing files between my phone and my PC has always been a pain. I’m looking at you MTP. But, with &lt;code&gt;termux&lt;/code&gt; and &lt;code&gt;sshd&lt;/code&gt; all set up, it’s as simple as:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;$ arp
Address         HWtype  HWad ...
192.168.43.187  ether   d0:0 ...

$ rsync -avz 192.168.43.187:~/frogs ~/pics/frogs&lt;/code&gt;&lt;/pre&gt;
&lt;h3 id="ssh-tmux"&gt;ssh &amp;amp; tmux&lt;/h3&gt;
&lt;p&gt;My phone doubles as a secondary view into my main machine with &lt;code&gt;ssh&lt;/code&gt; and &lt;code&gt;tmux&lt;/code&gt;. When I am away from my PC (read: sitting across the room), I check build status and IRC messages by &lt;code&gt;ssh&lt;/code&gt;ing into a tmux session running the said build or weechat.&lt;/p&gt;
&lt;h3 id="file-uploads"&gt;file uploads&lt;/h3&gt;
&lt;p&gt;Not being able to access my (ssh-only) file host was crippling. With a &lt;code&gt;bash&lt;/code&gt; instance on my phone, I just copied over my ssh keys, and popped in a file upload script (a glorified &lt;code&gt;scp&lt;/code&gt;). Now I just have to figure out a way to clean up these file names …&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;~/storage/pictures/ $ ls
02muf5g7b2i41.jpg  7alt3cwg77841.jpg  cl4bsrge7id11.png
mtZabXG.jpg        p8d5c584f2841.jpg  vjUxGjq.jpg&lt;/code&gt;&lt;/pre&gt;
&lt;h3 id="cmus"&gt;cmus&lt;/h3&gt;
&lt;p&gt;Alright, I don’t really listen to music via &lt;code&gt;cmus&lt;/code&gt;, but I did use it a couple times when my default music player was acting up. &lt;code&gt;cmus&lt;/code&gt; is a viable option:&lt;/p&gt;
&lt;p&gt;&lt;a href="https://u.peppe.rs/CP.jpg"&gt;&lt;img src="https://u.peppe.rs/CP.jpg" /&gt;&lt;/a&gt;&lt;/p&gt;</description>
<link>https://peppe.rs/posts/termux_tandem/</link>
<pubDate>Sat, 07 Mar 2020 18:30:00 +0000</pubDate>
<guid>https://peppe.rs/posts/termux_tandem/</guid>
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<item>
<title>Call To ARMs</title>
<description>&lt;p&gt;My 4th semester involves ARM programming. And proprietary tooling (Keil C). But we don’t do that here.&lt;/p&gt;
&lt;h3 id="building"&gt;Building&lt;/h3&gt;
&lt;p&gt;Assembling and linking ARM binaries on non-ARM architecture devices is fairly trivial. I went along with the GNU cross bare metal toolchain binutils, which provides &lt;code&gt;arm-as&lt;/code&gt; and &lt;code&gt;arm-ld&lt;/code&gt; (among a bunch of other utils that I don’t care about for now).&lt;/p&gt;
&lt;p&gt;Assemble &lt;code&gt;.s&lt;/code&gt; files with:&lt;/p&gt;
&lt;pre class="shell"&gt;&lt;code&gt;arm-none-eabi-as main.s -g -march=armv8.1-a -o main.out&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;The &lt;code&gt;-g&lt;/code&gt; flag generates extra debugging information that &lt;code&gt;gdb&lt;/code&gt; picks up. The &lt;code&gt;-march&lt;/code&gt; option establishes target architecture.&lt;/p&gt;
&lt;p&gt;Link &lt;code&gt;.o&lt;/code&gt; files with:&lt;/p&gt;
&lt;pre class="shell"&gt;&lt;code&gt;arm-none-eabi-ld main.out -o main&lt;/code&gt;&lt;/pre&gt;
&lt;h3 id="running-and-debugging"&gt;Running (and Debugging)&lt;/h3&gt;
&lt;p&gt;Things get interesting here. &lt;code&gt;gdb&lt;/code&gt; on your x86 machine cannot read nor execute binaries compiled for ARM. So, we simulate an ARM processor using &lt;code&gt;qemu&lt;/code&gt;. Now qemu allows you to run &lt;code&gt;gdbserver&lt;/code&gt; on startup. Connecting our local &lt;code&gt;gdb&lt;/code&gt; instance to &lt;code&gt;gdbserver&lt;/code&gt; gives us a view into the program’s execution. Easy!&lt;/p&gt;
&lt;p&gt;Run &lt;code&gt;qemu&lt;/code&gt;, with &lt;code&gt;gdbserver&lt;/code&gt; on port &lt;code&gt;1234&lt;/code&gt;, with our ARM binary, &lt;code&gt;main&lt;/code&gt;:&lt;/p&gt;
&lt;pre class="shell"&gt;&lt;code&gt;qemu-arm -singlestep -g 1234 main&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Start up &lt;code&gt;gdb&lt;/code&gt; on your machine, and connect to &lt;code&gt;qemu&lt;/code&gt;’s &lt;code&gt;gdbserver&lt;/code&gt;:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;(gdb) set architecture armv8-a
(gdb) target remote localhost:1234
(gdb) file main
Reading symbols from main...  # yay!&lt;/code&gt;&lt;/pre&gt;
&lt;h3 id="gdb-enhanced"&gt;GDB Enhanced&lt;/h3&gt;
&lt;p&gt;&lt;code&gt;gdb&lt;/code&gt; is cool, but it’s not nearly as comfortable as well fleshed out emulators/IDEs like Keil. Watching registers, CPSR and memory chunks update &lt;em&gt;is&lt;/em&gt; pretty fun.&lt;/p&gt;
&lt;p&gt;I came across &lt;code&gt;gdb&lt;/code&gt;’s TUI mode (hit &lt;code&gt;C-x C-a&lt;/code&gt; or type &lt;code&gt;tui enable&lt;/code&gt; at the prompt). TUI mode is a godsend. It highlights the current line of execution, shows you disassembly outputs, updated registers, active breakpoints and more.&lt;/p&gt;
&lt;p&gt;&lt;em&gt;But&lt;/em&gt;, it is an absolute eyesore.&lt;/p&gt;
&lt;p&gt;Say hello to &lt;a href="https://github.com/hugsy/gef"&gt;GEF&lt;/a&gt;! “GDB Enhanced Features” teaches our old dog some cool new tricks. Here are some additions that made my ARM debugging experience loads better:&lt;/p&gt;
&lt;ul&gt;
&lt;li&gt;Memory watches&lt;/li&gt;
&lt;li&gt;Register watches, with up to 7 levels of deref (overkill, I agree)&lt;/li&gt;
&lt;li&gt;Stack tracing&lt;/li&gt;
&lt;/ul&gt;
&lt;p&gt;And it’s pretty! See for yourself:&lt;/p&gt;
&lt;p&gt;&lt;a href="https://u.peppe.rs/wq.png"&gt;&lt;img src="https://u.peppe.rs/wq.png" /&gt;&lt;/a&gt;&lt;/p&gt;
&lt;h3 id="editing"&gt;Editing&lt;/h3&gt;
&lt;p&gt;Vim, with &lt;code&gt;syntax off&lt;/code&gt; because it dosen’t handle GNU ARM syntax too well.&lt;/p&gt;</description>
<link>https://peppe.rs/posts/call_to_ARMs/</link>
<pubDate>Fri, 07 Feb 2020 18:30:00 +0000</pubDate>
<guid>https://peppe.rs/posts/call_to_ARMs/</guid>
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<item>
<title>Color Conundrum</title>
<description>&lt;p&gt;This piece aims to highlight (pun intended) some of the reasons behind my &lt;a href="https://u.peppe.rs/bF.png"&gt;color free&lt;/a&gt; editor setup.&lt;/p&gt;
&lt;p&gt;Imagine highlighting an entire book because &lt;em&gt;all&lt;/em&gt; of it is important. That is exactly what (most) syntax highlighting does. It is difficult for the human eye to filter out noise in rainbow barf. Use color to draw attention, not diverge it.&lt;/p&gt;
&lt;p&gt;At the same time, a book devoid of color is &lt;em&gt;boring!&lt;/em&gt; What is the takeaway from this 10 line paragraph? What are the technical terms used?&lt;/p&gt;
&lt;p&gt;Prose and code are certainly different, but the fickle minded human eye is the same. The eye constantly looks for a frame of reference, a focal point. It grows tired when it can’t find one.&lt;/p&gt;
&lt;p&gt;The following comparison does a better job of explaining (none, ample and over-the-top highlighting, from left to right):&lt;/p&gt;
&lt;p&gt;&lt;a href="https://u.peppe.rs/lt.png"&gt;&lt;img src="https://u.peppe.rs/lt.png" /&gt;&lt;/a&gt;&lt;/p&gt;
&lt;p&gt;Without highlighting (far left), it is hard to differentiate between comments and code! The florid color scheme (far right) is no good either, it contains too many attention grabbers. The center sample is a healthy balance of both. Function calls and constants stand out, and repetitive keywords and other noise (&lt;code&gt;let&lt;/code&gt;, &lt;code&gt;as&lt;/code&gt;) are mildly dimmed out. Comments and non-code text (sign column, status text) are dimmed further.&lt;/p&gt;
&lt;p&gt;I’ll stop myself before I rant about color contrast and combinations.&lt;/p&gt;</description>
<link>https://peppe.rs/posts/color_conundrum/</link>
<pubDate>Mon, 30 Dec 2019 18:30:00 +0000</pubDate>
<guid>https://peppe.rs/posts/color_conundrum/</guid>
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<item>
<title>Static Sites With Bash</title>
<description>&lt;p&gt;After going through a bunch of static site generators (&lt;a href="https://blog.getpelican.com/"&gt;pelican&lt;/a&gt;, &lt;a href="https://gohugo.io"&gt;hugo&lt;/a&gt;, &lt;a href="https://github.com/icyphox/vite"&gt;vite&lt;/a&gt;), I decided to roll my own. If you are more of the ‘show me the code’ kinda guy, &lt;a href="https://github.com/nerdypepper/site"&gt;here&lt;/a&gt; you go.&lt;/p&gt;
&lt;h3 id="text-formatting"&gt;Text formatting&lt;/h3&gt;
&lt;p&gt;I chose to write in markdown, and convert to html with &lt;a href="https://kristaps.bsd.lv/lowdown/"&gt;lowdown&lt;/a&gt;.&lt;/p&gt;
&lt;h3 id="directory-structure"&gt;Directory structure&lt;/h3&gt;
&lt;p&gt;I host my site on GitHub pages, so &lt;code&gt;docs/&lt;/code&gt; has to be the entry point. Markdown formatted posts go into &lt;code&gt;posts/&lt;/code&gt;, get converted into html, and end up in &lt;code&gt;docs/index.html&lt;/code&gt;, something like this:&lt;/p&gt;
&lt;div class="sourceCode" id="cb1"&gt;&lt;pre class="sourceCode bash"&gt;&lt;code class="sourceCode bash"&gt;&lt;span id="cb1-1"&gt;&lt;a href="#cb1-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="va"&gt;posts=$(&lt;/span&gt;&lt;span class="fu"&gt;ls&lt;/span&gt; -t ./posts&lt;span class="va"&gt;)&lt;/span&gt;     # &lt;span class="ex"&gt;chronological&lt;/span&gt; order!&lt;/span&gt;
&lt;span id="cb1-2"&gt;&lt;a href="#cb1-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;for&lt;/span&gt; &lt;span class="ex"&gt;f&lt;/span&gt; in &lt;span class="va"&gt;$posts&lt;/span&gt;&lt;span class="kw"&gt;;&lt;/span&gt; &lt;span class="kw"&gt;do&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-3"&gt;&lt;a href="#cb1-3" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="va"&gt;file=&lt;/span&gt;&lt;span class="st"&gt;&amp;quot;./posts/&amp;quot;&lt;/span&gt;&lt;span class="va"&gt;$f&lt;/span&gt;      # &lt;span class="kw"&gt;`&lt;/span&gt;&lt;span class="fu"&gt;ls&lt;/span&gt;&lt;span class="kw"&gt;`&lt;/span&gt; &lt;span class="ex"&gt;mangled&lt;/span&gt; our file paths&lt;/span&gt;
&lt;span id="cb1-4"&gt;&lt;a href="#cb1-4" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="bu"&gt;echo&lt;/span&gt; &lt;span class="st"&gt;&amp;quot;generating post &lt;/span&gt;&lt;span class="va"&gt;$file&lt;/span&gt;&lt;span class="st"&gt;&amp;quot;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-5"&gt;&lt;a href="#cb1-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb1-6"&gt;&lt;a href="#cb1-6" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="va"&gt;html=$(&lt;/span&gt;&lt;span class="ex"&gt;lowdown&lt;/span&gt; &lt;span class="st"&gt;&amp;quot;&lt;/span&gt;&lt;span class="va"&gt;$file&lt;/span&gt;&lt;span class="st"&gt;&amp;quot;&lt;/span&gt;&lt;span class="va"&gt;)&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb1-7"&gt;&lt;a href="#cb1-7" aria-hidden="true"&gt;&lt;/a&gt;    &lt;span class="bu"&gt;echo&lt;/span&gt; -e &lt;span class="st"&gt;&amp;quot;html&amp;quot;&lt;/span&gt; &lt;span class="op"&gt;&amp;gt;&amp;gt;&lt;/span&gt; docs/index.html&lt;/span&gt;
&lt;span id="cb1-8"&gt;&lt;a href="#cb1-8" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="kw"&gt;done&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;h3 id="assets"&gt;Assets&lt;/h3&gt;
&lt;p&gt;Most static site generators recommend dropping image assets into the site source itself. That does have it’s merits, but I prefer hosting images separately:&lt;/p&gt;
&lt;div class="sourceCode" id="cb2"&gt;&lt;pre class="sourceCode bash"&gt;&lt;code class="sourceCode bash"&gt;&lt;span id="cb2-1"&gt;&lt;a href="#cb2-1" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;# strip file extension&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-2"&gt;&lt;a href="#cb2-2" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="va"&gt;ext=&lt;/span&gt;&lt;span class="st"&gt;&amp;quot;&lt;/span&gt;&lt;span class="va"&gt;${1##&lt;/span&gt;*.&lt;span class="va"&gt;}&lt;/span&gt;&lt;span class="st"&gt;&amp;quot;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-3"&gt;&lt;a href="#cb2-3" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb2-4"&gt;&lt;a href="#cb2-4" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;# generate a random file name&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-5"&gt;&lt;a href="#cb2-5" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="va"&gt;id=$(&lt;/span&gt; &lt;span class="fu"&gt;cat&lt;/span&gt; /dev/urandom &lt;span class="kw"&gt;|&lt;/span&gt; &lt;span class="fu"&gt;tr&lt;/span&gt; -dc &lt;span class="st"&gt;&amp;#39;a-zA-Z0-9&amp;#39;&lt;/span&gt; &lt;span class="kw"&gt;|&lt;/span&gt; &lt;span class="ex"&gt;fold&lt;/span&gt; -w 2 &lt;span class="kw"&gt;|&lt;/span&gt; &lt;span class="fu"&gt;head&lt;/span&gt; -n 1 &lt;span class="va"&gt;)&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-6"&gt;&lt;a href="#cb2-6" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="va"&gt;id=&lt;/span&gt;&lt;span class="st"&gt;&amp;quot;&lt;/span&gt;&lt;span class="va"&gt;$id&lt;/span&gt;&lt;span class="st"&gt;.&lt;/span&gt;&lt;span class="va"&gt;$ext&lt;/span&gt;&lt;span class="st"&gt;&amp;quot;&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-7"&gt;&lt;a href="#cb2-7" aria-hidden="true"&gt;&lt;/a&gt;&lt;/span&gt;
&lt;span id="cb2-8"&gt;&lt;a href="#cb2-8" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="co"&gt;# copy to my file host&lt;/span&gt;&lt;/span&gt;
&lt;span id="cb2-9"&gt;&lt;a href="#cb2-9" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="fu"&gt;scp&lt;/span&gt; -P 443 &lt;span class="st"&gt;&amp;quot;&lt;/span&gt;&lt;span class="va"&gt;$1&lt;/span&gt;&lt;span class="st"&gt;&amp;quot;&lt;/span&gt; emerald:files/&lt;span class="st"&gt;&amp;quot;&lt;/span&gt;&lt;span class="va"&gt;$id&lt;/span&gt;&lt;span class="st"&gt;&amp;quot;&lt;/span&gt; &lt;/span&gt;
&lt;span id="cb2-10"&gt;&lt;a href="#cb2-10" aria-hidden="true"&gt;&lt;/a&gt;&lt;span class="bu"&gt;echo&lt;/span&gt; &lt;span class="st"&gt;&amp;quot;https://u.peppe.rs/&lt;/span&gt;&lt;span class="va"&gt;$id&lt;/span&gt;&lt;span class="st"&gt;&amp;quot;&lt;/span&gt;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;h3 id="templating"&gt;Templating&lt;/h3&gt;
&lt;p&gt;&lt;a href="https://github.com/NerdyPepper/site/blob/master/generate.sh"&gt;&lt;code&gt;generate.sh&lt;/code&gt;&lt;/a&gt; brings the above bits and pieces together (with some extra cruft to avoid javascript). It uses &lt;code&gt;sed&lt;/code&gt; to produce nice titles from the file names (removes underscores, title-case), and &lt;code&gt;date(1)&lt;/code&gt; to add the date to each post listing!&lt;/p&gt;</description>
<link>https://peppe.rs/posts/static_sites_with_bash/</link>
<pubDate>Fri, 22 Nov 2019 18:30:00 +0000</pubDate>
<guid>https://peppe.rs/posts/static_sites_with_bash/</guid>
</item>
<item>
<title>My Setup</title>
<description>&lt;p&gt;Decided to do one of these because everyone does one of these.&lt;/p&gt;
&lt;p&gt;&lt;img src="https://u.peppe.rs/Hb.png" /&gt;&lt;/p&gt;
&lt;p&gt;My entire setup is managed with GNU &lt;code&gt;stow&lt;/code&gt;, making it easier to replicate on fresh installations. You can find my configuration files on &lt;a href="https://github.com/nerdypepper"&gt;GitHub&lt;/a&gt;.&lt;/p&gt;
&lt;p&gt;I run Void Linux (glibc) on my &lt;a href="https://store.hp.com/us/en/mdp/laptops/envy-13"&gt;HP Envy 13" (2018)&lt;/a&gt;. To keep things simple, I run a raw X session with &lt;code&gt;2bwm&lt;/code&gt; as my window manager, along with &lt;code&gt;dunst&lt;/code&gt; (notification daemon) and Sam’s &lt;a href="https://github.com/sdhand/compton"&gt;&lt;code&gt;compton&lt;/code&gt;&lt;/a&gt; (compositor) fork.&lt;/p&gt;
&lt;p&gt;I am a fan of GNU tools, so I use &lt;code&gt;bash&lt;/code&gt; as my shell, and &lt;code&gt;coreutils&lt;/code&gt; to manage files, archives, strings, paths etc. I edit files with &lt;code&gt;vim&lt;/code&gt;, chat with &lt;code&gt;weechat&lt;/code&gt;, listen to music with &lt;code&gt;cmus&lt;/code&gt;, monitor processes with &lt;code&gt;htop&lt;/code&gt;, manage sessions with &lt;code&gt;tmux&lt;/code&gt;, read pdfs in &lt;code&gt;zathura&lt;/code&gt;. I rarely ever leave the comfort of my terminal emulator, &lt;code&gt;urxvt&lt;/code&gt;.&lt;/p&gt;
&lt;p&gt;Most of my academic typesetting is done with TeX, and compiled with &lt;code&gt;xelatex&lt;/code&gt;. Other &lt;em&gt;fun&lt;/em&gt; documents are made with GIMP :).&lt;/p&gt;</description>
<link>https://peppe.rs/posts/my_setup/</link>
<pubDate>Wed, 06 Nov 2019 18:30:00 +0000</pubDate>
<guid>https://peppe.rs/posts/my_setup/</guid>
</item>
<item>
<title>WPA Woes</title>
<description>&lt;p&gt;I finally got around to installing Void GNU/Linux on my main computer. Rolling release, non-systemd, need I say more?&lt;/p&gt;
&lt;p&gt;As with all GNU/Linux distributions, wireless networks had me in a fix. If you can see this post, it means I’ve managed to get online. It turns out, &lt;code&gt;wpa_supplicant&lt;/code&gt; was detecting the wrong interface by default (does it ever select the right one?). Let us fix that:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;$ sudo rm -r /var/service/wpa_supplicant
$ sudo killall dhcpcd&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;What is the right interface though?&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;$ iw dev
   ...
   Interface wlp2s0
   ...&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Aha! Let us run &lt;code&gt;wpa_supplicant&lt;/code&gt; on that interface, as a background process:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;$ sudo wpa_supplicant -B -i wlp2s0 -c /etc/wpa_supplicant/wpa_supplicant.conf
$ sudo dhcpcd -B wlp2s0
$ ping google.com
PING ...&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Yay! Make those changes perpetual by enabling the service:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;------------------------------------------------------
# Add these to /etc/wpa_supplicant/wpa_supplicant.conf
OPTS=&amp;quot;-B&amp;quot;
WPA_INTERFACE=&amp;quot;wlp2s0&amp;quot;
------------------------------------------------------
$ sudo ln -s /etc/sv/wpa_supplicant /var/service/
$ sudo ln -s /etc/sv/dhcpcd /var/service/
$ sudo sv restart wpa_supplicant
$ sudo sv restart dhcpcd&lt;/code&gt;&lt;/pre&gt;</description>
<link>https://peppe.rs/posts/WPA_woes/</link>
<pubDate>Sat, 12 Oct 2019 16:23:00 +0000</pubDate>
<guid>https://peppe.rs/posts/WPA_woes/</guid>
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<item>
<title>Bye Bye BDFs</title>
<description>&lt;p&gt;Glyph Bitmap Distribution Format is no more, as the creators of &lt;a href="https://pango.org"&gt;Pango&lt;/a&gt;, one of the most widely used text rendering libraries, &lt;a href="https://blogs.gnome.org/mclasen/2019/05/25/pango-future-directions/"&gt;announced&lt;/a&gt; their plans for Pango 1.44.&lt;/p&gt;
&lt;p&gt;Until recently, Pango used FreeType to draw fonts. They will be moving over to &lt;a href="https://harfbuzz.org"&gt;Harfbuzz&lt;/a&gt;, an evolution of FreeType.&lt;/p&gt;
&lt;p&gt;&lt;em&gt;Why?&lt;/em&gt;&lt;/p&gt;
&lt;p&gt;In short, FreeType was hard to work with. It required complex logic, and provided no advantage over Harfbuzz (other than being able to fetch opentype metrics with ease).&lt;/p&gt;
&lt;p&gt;Upgrading to Pango v1.44 will break your GTK applications (if you use a &lt;code&gt;bdf&lt;/code&gt;/&lt;code&gt;pcf&lt;/code&gt; bitmap font). Harfbuzz &lt;em&gt;does&lt;/em&gt; support bitmap-only OpenType fonts, &lt;code&gt;otb&lt;/code&gt;s. Convert your existing fonts over to &lt;code&gt;otb&lt;/code&gt;s using &lt;a href="https://fontforge.github.io"&gt;FontForge&lt;/a&gt;. It is to be noted that applications such as &lt;code&gt;xterm&lt;/code&gt; and &lt;code&gt;rxvt&lt;/code&gt; use &lt;code&gt;xft&lt;/code&gt; (X FreeType) to render fonts, and will remain unaffected by the update.&lt;/p&gt;
&lt;p&gt;Both &lt;a href="https://github.com/nerdypepper/scientifica"&gt;scientifica&lt;/a&gt; and &lt;a href="https://github.com/nerdypepper/curie"&gt;curie&lt;/a&gt; will soon ship with bitmap-only OpenType font formats.&lt;/p&gt;</description>
<link>https://peppe.rs/posts/bye_bye_BDFs/</link>
<pubDate>Wed, 07 Aug 2019 17:26:00 +0000</pubDate>
<guid>https://peppe.rs/posts/bye_bye_BDFs/</guid>
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<item>
<title>Onivim Sucks</title>
<description>&lt;p&gt;&lt;a href="https://v2.onivim.io"&gt;Onivim&lt;/a&gt; is a ‘modern modal editor’, combining fancy interface and language features with vim-style modal editing. What’s wrong you ask?&lt;/p&gt;
&lt;p&gt;Apart from &lt;a href="https://github.com/onivim/oni2/issues/550"&gt;buggy syntax highlighting&lt;/a&gt;, &lt;a href="https://github.com/onivim/oni2/issues/519"&gt;broken scrolling&lt;/a&gt; and &lt;a href="https://github.com/onivim/oni2/issues?q=is%3Aissue+label%3A%22daily+editor+blocker%22+is%3Aopen"&gt;others&lt;/a&gt;, Onivim is &lt;strong&gt;proprietary&lt;/strong&gt; software. It is licensed under a commercial &lt;a href="https://github.com/onivim/oni1/blob/master/Outrun-Labs-EULA-v1.1.md"&gt;end user agreement license&lt;/a&gt;, which prohibits redistribution in both object code and source code formats.&lt;/p&gt;
&lt;p&gt;Onivim’s core editor logic (bits that belong to vim), have been separated from the interface, into &lt;a href="https://github.com/onivim/libvim"&gt;libvim&lt;/a&gt;. libvim is licensed under MIT, which means, this ‘extension’ of vim is perfectly in adherence to &lt;a href="http://vimdoc.sourceforge.net/htmldoc/uganda.html#license"&gt;vim’s license text&lt;/a&gt;! Outrun Labs are exploiting this loophole (distributing vim as a library) to commercialize Onivim.&lt;/p&gt;
&lt;p&gt;Onivim’s source code is available on &lt;a href="https://github.com/onivim/oni2"&gt;GitHub&lt;/a&gt;. They do mention that the source code trickles down to the &lt;a href="https://github.com/onivim/oni2-mit"&gt;oni2-mit&lt;/a&gt; repository, which (not yet) contains MIT-licensed code, &lt;strong&gt;18 months&lt;/strong&gt; after each commit to the original repository.&lt;/p&gt;
&lt;p&gt;Want to contribute to Onivim? Don’t. They make a profit out of your contributions. Currently, Onivim is priced at $19.99, ‘pre-alpha’ pricing which is 80% off the final price! If you are on the lookout for an editor, I would suggest using &lt;a href="https://vim.org"&gt;Vim&lt;/a&gt;, charity ware that actually works, and costs $100 lesser.&lt;/p&gt;</description>
<link>https://peppe.rs/posts/onivim_sucks/</link>
<pubDate>Fri, 02 Aug 2019 16:32:00 +0000</pubDate>
<guid>https://peppe.rs/posts/onivim_sucks/</guid>
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<item>
<title>Bash Harder With Vim</title>
<description>&lt;p&gt;Bash is tricky, don’t let your editor get in your way. Here’s a couple of neat additions you could make to your &lt;code&gt;vimrc&lt;/code&gt; for a better shell programming experience.&lt;/p&gt;
&lt;h3 id="man-pages-inside-vim"&gt;Man pages inside vim&lt;/h3&gt;
&lt;p&gt;Source this script to get started:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;runtime ftplugin/man.vim&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Now, you can open manpages inside vim with &lt;code&gt;:Man&lt;/code&gt;! It adds nicer syntax highlighting and the ability to jump around with &lt;code&gt;Ctrl-]&lt;/code&gt; and &lt;code&gt;Ctrl-T&lt;/code&gt;.&lt;/p&gt;
&lt;p&gt;By default, the manpage is opened in a horizontal split, I prefer using a new tab:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;let g:ft_man_open_mode = &amp;#39;tab&amp;#39;&lt;/code&gt;&lt;/pre&gt;
&lt;h3 id="scratchpad-to-test-your-commands"&gt;Scratchpad to test your commands&lt;/h3&gt;
&lt;p&gt;I often test my &lt;code&gt;sed&lt;/code&gt; substitutions, here is a sample from the script used to generate this site:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;# a substitution to convert snake_case to Title Case With Spaces
echo &amp;quot;$1&amp;quot; | sed -E -e &amp;quot;s/\..+$//g&amp;quot;  -e &amp;quot;s/_(.)/ \u\1/g&amp;quot; -e &amp;quot;s/^(.)/\u\1/g&amp;quot;&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;Instead of dropping into a new shell, just test it out directly from vim!&lt;/p&gt;
&lt;ul&gt;
&lt;li&gt;Yank the line into a register:&lt;/li&gt;
&lt;/ul&gt;
&lt;pre&gt;&lt;code&gt;yy&lt;/code&gt;&lt;/pre&gt;
&lt;ul&gt;
&lt;li&gt;Paste it into the command-line window:&lt;/li&gt;
&lt;/ul&gt;
&lt;pre&gt;&lt;code&gt;q:p&lt;/code&gt;&lt;/pre&gt;
&lt;ul&gt;
&lt;li&gt;Make edits as required:&lt;/li&gt;
&lt;/ul&gt;
&lt;pre&gt;&lt;code&gt;syntax off            # previously run commands
edit index.html       # in a buffer!
w | so %
!echo &amp;quot;new_post.md&amp;quot; | sed -E -e &amp;quot;s/\..+$//g&amp;quot;  --snip--
^--- note the use of &amp;#39;!&amp;#39;&lt;/code&gt;&lt;/pre&gt;
&lt;ul&gt;
&lt;li&gt;Hit enter with the cursor on the line containing your command!&lt;/li&gt;
&lt;/ul&gt;
&lt;pre&gt;&lt;code&gt;$ vim
New Post         # output
Press ENTER or type command to continue&lt;/code&gt;&lt;/pre&gt;</description>
<link>https://peppe.rs/posts/bash_harder_with_vim/</link>
<pubDate>Tue, 30 Jul 2019 18:30:00 +0000</pubDate>
<guid>https://peppe.rs/posts/bash_harder_with_vim/</guid>
</item>
<item>
<title>Hold Position!</title>
<description>&lt;p&gt;Often times, when I run a vim command that makes “big” changes to a file (a macro or a &lt;code&gt;:vimgrep&lt;/code&gt; command) I lose my original position and feel disoriented.&lt;/p&gt;
&lt;p&gt;&lt;em&gt;Save position with &lt;code&gt;winsaveview()&lt;/code&gt;!&lt;/em&gt;&lt;/p&gt;
&lt;p&gt;The &lt;code&gt;winsaveview()&lt;/code&gt; command returns a &lt;code&gt;Dictionary&lt;/code&gt; that contains information about the view of the current window. This includes the cursor line number, cursor coloumn, the top most line in the window and a couple of other values, none of which concern us.&lt;/p&gt;
&lt;p&gt;Before running our command (one that jumps around the buffer, a lot), we save our view, and restore it once its done, with &lt;code&gt;winrestview&lt;/code&gt;.&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;let view = winsaveview()
s/\s\+$//gc              &amp;quot; find and (confirm) replace trailing blanks
winrestview(view)        &amp;quot; restore our original view!&lt;/code&gt;&lt;/pre&gt;
&lt;p&gt;It might seem a little overkill in the above example, just use `` (double backticks) instead, but it comes in handy when you run your file through heavier filtering.&lt;/p&gt;</description>
<link>https://peppe.rs/posts/hold_position!/</link>
<pubDate>Tue, 30 Jul 2019 14:45:00 +0000</pubDate>
<guid>https://peppe.rs/posts/hold_position!/</guid>
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<item>
<title>Get Better At Yanking And Putting In Vim</title>
<description>&lt;p&gt;a couple of nifty tricks to help you copy-paste better:&lt;/p&gt;
&lt;ol type="1"&gt;
&lt;li&gt;&lt;p&gt;reselecting previously selected text (i use this to fix botched selections):&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;gv  &amp;quot; :h gv for more
    &amp;quot; you can use `o` in visual mode to go to the `Other` end of the selection
    &amp;quot; use a motion to fix the selection&lt;/code&gt;&lt;/pre&gt;&lt;/li&gt;
&lt;li&gt;&lt;p&gt;reselecting previously yanked text:&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;`[v`]
`[         &amp;quot; marks the beginning of the previously yanked text   :h `[
`]         &amp;quot; marks the end                                       :h `]
 v         &amp;quot; visual select everything in between

nnoremap gb `[v`]    &amp;quot; &amp;quot;a quick map to perform the above&lt;/code&gt;&lt;/pre&gt;&lt;/li&gt;
&lt;li&gt;&lt;p&gt;pasting and indenting text (in one go):&lt;/p&gt;
&lt;pre&gt;&lt;code&gt;]p   &amp;quot; put (p) and adjust indent to current line
]P   &amp;quot; put the text before the cursor (P) and adjust indent to current line&lt;/code&gt;&lt;/pre&gt;&lt;/li&gt;
&lt;/ol&gt;</description>
<link>https://peppe.rs/posts/get_better_at_yanking_and_putting_in_vim/</link>
<pubDate>Tue, 30 Jul 2019 08:43:00 +0000</pubDate>
<guid>https://peppe.rs/posts/get_better_at_yanking_and_putting_in_vim/</guid>
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