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Diffstat (limited to 'docs/posts/auto-currying_rust_functions')
| -rw-r--r-- | docs/posts/auto-currying_rust_functions/index.html | 496 |
1 files changed, 367 insertions, 129 deletions
diff --git a/docs/posts/auto-currying_rust_functions/index.html b/docs/posts/auto-currying_rust_functions/index.html index 0d6fc77..7b05aeb 100644 --- a/docs/posts/auto-currying_rust_functions/index.html +++ b/docs/posts/auto-currying_rust_functions/index.html | |||
| @@ -28,7 +28,7 @@ | |||
| 28 | 09/05 — 2020 | 28 | 09/05 — 2020 |
| 29 | <div class="stats"> | 29 | <div class="stats"> |
| 30 | <span class="stats-number"> | 30 | <span class="stats-number"> |
| 31 | 356.43 | 31 | 356.44 |
| 32 | </span> | 32 | </span> |
| 33 | <span class="stats-unit">cm</span> | 33 | <span class="stats-unit">cm</span> |
| 34 |   | 34 |   |
| @@ -42,13 +42,22 @@ | |||
| 42 | Auto-currying Rust Functions | 42 | Auto-currying Rust Functions |
| 43 | </h1> | 43 | </h1> |
| 44 | <div class="post-text"> | 44 | <div class="post-text"> |
| 45 | <p>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 <a href="https://github.com/nerdypepper/cutlass">here</a>. It is also available on <a href="https://crates.io/crates/cutlass">crates.io</a>.</p> | 45 | <p>This post contains a gentle introduction to procedural macros in Rust |
| 46 | <p>The following links might prove to be useful before getting started:</p> | 46 | and a guide to writing a procedural macro to curry Rust functions. The |
| 47 | source code for the entire library can be found <a | ||
| 48 | href="https://github.com/nerdypepper/cutlass">here</a>. It is also | ||
| 49 | available on <a | ||
| 50 | href="https://crates.io/crates/cutlass">crates.io</a>.</p> | ||
| 51 | <p>The following links might prove to be useful before getting | ||
| 52 | started:</p> | ||
| 47 | <ul> | 53 | <ul> |
| 48 | <li><a href="https://doc.rust-lang.org/reference/procedural-macros.html">Procedural Macros</a></li> | 54 | <li><a |
| 55 | href="https://doc.rust-lang.org/reference/procedural-macros.html">Procedural | ||
| 56 | Macros</a></li> | ||
| 49 | <li><a href="https://en.wikipedia.org/wiki/Currying">Currying</a></li> | 57 | <li><a href="https://en.wikipedia.org/wiki/Currying">Currying</a></li> |
| 50 | </ul> | 58 | </ul> |
| 51 | <p>Or you can pretend you read them, because I have included a primer here :)</p> | 59 | <p>Or you can pretend you read them, because I have included a primer |
| 60 | here :)</p> | ||
| 52 | <h3 id="contents">Contents</h3> | 61 | <h3 id="contents">Contents</h3> |
| 53 | <ol type="1"> | 62 | <ol type="1"> |
| 54 | <li><a href="#currying">Currying</a><br /> | 63 | <li><a href="#currying">Currying</a><br /> |
| @@ -73,7 +82,12 @@ | |||
| 73 | <li><a href="#conclusion">Conclusion</a></li> | 82 | <li><a href="#conclusion">Conclusion</a></li> |
| 74 | </ol> | 83 | </ol> |
| 75 | <h3 id="currying">Currying</h3> | 84 | <h3 id="currying">Currying</h3> |
| 76 | <p>Currying is the process of transformation of a function call like <code>f(a, b, c)</code> to <code>f(a)(b)(c)</code>. 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 <em>curried function</em>, that returns after receiving 2 arguments.</p> | 85 | <p>Currying is the process of transformation of a function call like |
| 86 | <code>f(a, b, c)</code> to <code>f(a)(b)(c)</code>. A curried function | ||
| 87 | returns a concrete value only when it receives all its arguments! If it | ||
| 88 | does recieve an insufficient amount of arguments, say 1 of 3, it returns | ||
| 89 | a <em>curried function</em>, that returns after receiving 2 | ||
| 90 | arguments.</p> | ||
| 77 | <pre><code>curry(f(a, b, c)) = h(a)(b)(c) | 91 | <pre><code>curry(f(a, b, c)) = h(a)(b)(c) |
| 78 | 92 | ||
| 79 | h(x) = g <- curried function that takes upto 2 args (g) | 93 | h(x) = g <- curried function that takes upto 2 args (g) |
| @@ -82,49 +96,86 @@ k(z) = v <- a value (v) | |||
| 82 | 96 | ||
| 83 | Keen readers will conclude the following, | 97 | Keen readers will conclude the following, |
| 84 | h(x)(y)(z) = g(y)(z) = k(z) = v</code></pre> | 98 | h(x)(y)(z) = g(y)(z) = k(z) = v</code></pre> |
| 85 | <p>Mathematically, if <code>f</code> is a function that takes two arguments <code>x</code> and <code>y</code>, such that <code>x ϵ X</code>, and <code>y ϵ Y</code> , we write it as:</p> | 99 | <p>Mathematically, if <code>f</code> is a function that takes two |
| 100 | arguments <code>x</code> and <code>y</code>, such that | ||
| 101 | <code>x ϵ X</code>, and <code>y ϵ Y</code> , we write it as:</p> | ||
| 86 | <pre><code>f: (X × Y) -> Z</code></pre> | 102 | <pre><code>f: (X × Y) -> Z</code></pre> |
| 87 | <p>where <code>×</code> denotes the Cartesian product of set <code>X</code> and <code>Y</code>, and curried <code>f</code> (denoted by <code>h</code> here) is written as:</p> | 103 | <p>where <code>×</code> denotes the Cartesian product of set |
| 104 | <code>X</code> and <code>Y</code>, and curried <code>f</code> (denoted | ||
| 105 | by <code>h</code> here) is written as:</p> | ||
| 88 | <pre><code>h: X -> (Y -> Z)</code></pre> | 106 | <pre><code>h: X -> (Y -> Z)</code></pre> |
| 89 | <h3 id="procedural-macros">Procedural Macros</h3> | 107 | <h3 id="procedural-macros">Procedural Macros</h3> |
| 90 | <p>These are functions that take code as input and spit out modified code as output. Powerful stuff. Rust has three kinds of proc-macros:</p> | 108 | <p>These are functions that take code as input and spit out modified |
| 109 | code as output. Powerful stuff. Rust has three kinds of proc-macros:</p> | ||
| 91 | <ul> | 110 | <ul> |
| 92 | <li>Function like macros<br /> | 111 | <li>Function like macros<br /> |
| 93 | </li> | 112 | </li> |
| 94 | <li>Derive macros: <code>#[derive(...)]</code>, used to automatically implement traits for structs/enums<br /> | 113 | <li>Derive macros: <code>#[derive(...)]</code>, used to automatically |
| 114 | implement traits for structs/enums<br /> | ||
| 95 | </li> | 115 | </li> |
| 96 | <li>and Attribute macros: <code>#[test]</code>, usually slapped onto functions</li> | 116 | <li>and Attribute macros: <code>#[test]</code>, usually slapped onto |
| 117 | functions</li> | ||
| 97 | </ul> | 118 | </ul> |
| 98 | <p>We will be using Attribute macros to convert a Rust function into a curried Rust function, which we should be able to call via: <code>function(arg1)(arg2)</code>.</p> | 119 | <p>We will be using Attribute macros to convert a Rust function into a |
| 120 | curried Rust function, which we should be able to call via: | ||
| 121 | <code>function(arg1)(arg2)</code>.</p> | ||
| 99 | <h3 id="definitions">Definitions</h3> | 122 | <h3 id="definitions">Definitions</h3> |
| 100 | <p>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:</p> | 123 | <p>Being respectable programmers, we define the input to and the output |
| 101 | <div class="sourceCode" id="cb4"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add(x<span class="op">:</span> <span class="dt">u32</span><span class="op">,</span> y<span class="op">:</span> <span class="dt">u32</span><span class="op">,</span> z<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> <span class="dt">u32</span> <span class="op">{</span></span> | 124 | from our proc-macro. Here’s a good non-trivial function to start out |
| 102 | <span id="cb4-2"><a href="#cb4-2" aria-hidden="true" tabindex="-1"></a> <span class="kw">return</span> x <span class="op">+</span> y <span class="op">+</span> z<span class="op">;</span></span> | 125 | with:</p> |
| 126 | <div class="sourceCode" id="cb4"><pre | ||
| 127 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add(x<span class="op">:</span> <span class="dt">u32</span><span class="op">,</span> y<span class="op">:</span> <span class="dt">u32</span><span class="op">,</span> z<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> <span class="dt">u32</span> <span class="op">{</span></span> | ||
| 128 | <span id="cb4-2"><a href="#cb4-2" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> x <span class="op">+</span> y <span class="op">+</span> z<span class="op">;</span></span> | ||
| 103 | <span id="cb4-3"><a href="#cb4-3" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> | 129 | <span id="cb4-3"><a href="#cb4-3" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> |
| 104 | <p>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:</p> | 130 | <p>Hmm, what would our output look like? What should our proc-macro |
| 105 | <div class="sourceCode" id="cb5"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add_curried1(x<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> <span class="op">?</span> <span class="op">{</span></span> | 131 | generate ideally? Well, if we understood currying correctly, we should |
| 106 | <span id="cb5-2"><a href="#cb5-2" aria-hidden="true" tabindex="-1"></a> <span class="kw">return</span> <span class="kw">fn</span> add_curried2 (y<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> <span class="op">?</span> <span class="op">{</span></span> | 132 | accept an argument and return a function that accepts an argument and |
| 107 | <span id="cb5-3"><a href="#cb5-3" aria-hidden="true" tabindex="-1"></a> <span class="kw">return</span> <span class="kw">fn</span> add_curried3 (z<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> <span class="dt">u32</span> <span class="op">{</span></span> | 133 | returns … you get the point. Something like this should do:</p> |
| 108 | <span id="cb5-4"><a href="#cb5-4" aria-hidden="true" tabindex="-1"></a> <span class="kw">return</span> x <span class="op">+</span> y <span class="op">+</span> z<span class="op">;</span></span> | 134 | <div class="sourceCode" id="cb5"><pre |
| 135 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add_curried1(x<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> <span class="op">?</span> <span class="op">{</span></span> | ||
| 136 | <span id="cb5-2"><a href="#cb5-2" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> <span class="kw">fn</span> add_curried2 (y<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> <span class="op">?</span> <span class="op">{</span></span> | ||
| 137 | <span id="cb5-3"><a href="#cb5-3" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> <span class="kw">fn</span> add_curried3 (z<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> <span class="dt">u32</span> <span class="op">{</span></span> | ||
| 138 | <span id="cb5-4"><a href="#cb5-4" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> x <span class="op">+</span> y <span class="op">+</span> z<span class="op">;</span></span> | ||
| 109 | <span id="cb5-5"><a href="#cb5-5" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> | 139 | <span id="cb5-5"><a href="#cb5-5" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> |
| 110 | <span id="cb5-6"><a href="#cb5-6" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> | 140 | <span id="cb5-6"><a href="#cb5-6" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> |
| 111 | <span id="cb5-7"><a href="#cb5-7" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> | 141 | <span id="cb5-7"><a href="#cb5-7" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> |
| 112 | <p>A couple of things to note:</p> | 142 | <p>A couple of things to note:</p> |
| 113 | <p><strong>Return types</strong><br /> | 143 | <p><strong>Return types</strong><br /> |
| 114 | We have placed <code>?</code>s in place of return types. Let’s try to fix that. <code>add_curried3</code> returns the ‘value’, so <code>u32</code> is accurate. <code>add_curried2</code> returns <code>add_curried3</code>. What is the type of <code>add_curried3</code>? It is a function that takes in a <code>u32</code> and returns a <code>u32</code>. So a <code>fn(u32) -> u32</code> will do right? No, I’ll explain why in the next point, but for now, we will make use of the <code>Fn</code> trait, our return type is <code>impl Fn(u32) -> u32</code>. This basically tells the compiler that we will be returning something function-like, a.k.a, behaves like a <code>Fn</code>. Cool!</p> | 144 | We have placed <code>?</code>s in place of return types. Let’s try to |
| 115 | <p>If you have been following along, you should be able to tell that the return type of <code>add_curried1</code> is:</p> | 145 | fix that. <code>add_curried3</code> returns the ‘value’, so |
| 146 | <code>u32</code> is accurate. <code>add_curried2</code> returns | ||
| 147 | <code>add_curried3</code>. What is the type of | ||
| 148 | <code>add_curried3</code>? It is a function that takes in a | ||
| 149 | <code>u32</code> and returns a <code>u32</code>. So a | ||
| 150 | <code>fn(u32) -> u32</code> will do right? No, I’ll explain why in | ||
| 151 | the next point, but for now, we will make use of the <code>Fn</code> | ||
| 152 | trait, our return type is <code>impl Fn(u32) -> u32</code>. This | ||
| 153 | basically tells the compiler that we will be returning something | ||
| 154 | function-like, a.k.a, behaves like a <code>Fn</code>. Cool!</p> | ||
| 155 | <p>If you have been following along, you should be able to tell that the | ||
| 156 | return type of <code>add_curried1</code> is:</p> | ||
| 116 | <pre><code>impl Fn(u32) -> (impl Fn(u32) -> u32)</code></pre> | 157 | <pre><code>impl Fn(u32) -> (impl Fn(u32) -> u32)</code></pre> |
| 117 | <p>We can drop the parentheses because <code>-></code> is right associative:</p> | 158 | <p>We can drop the parentheses because <code>-></code> is right |
| 159 | associative:</p> | ||
| 118 | <pre><code>impl Fn(u32) -> impl Fn(u32) -> u32 | 160 | <pre><code>impl Fn(u32) -> impl Fn(u32) -> u32 |
| 119 | </code></pre> | 161 | </code></pre> |
| 120 | <p><strong>Accessing environment</strong><br /> | 162 | <p><strong>Accessing environment</strong><br /> |
| 121 | A function cannot access it’s environment. Our solution will not work. <code>add_curried3</code> attempts to access <code>x</code>, which is not allowed! A closure<a href="#fn1" class="footnote-ref" id="fnref1" role="doc-noteref"><sup>1</sup></a> however, can. If we are returning a closure, our return type must be <code>impl Fn</code>, and not <code>fn</code>. The difference between the <code>Fn</code> trait and function pointers is beyond the scope of this post.</p> | 163 | A function cannot access it’s environment. Our solution will not work. |
| 164 | <code>add_curried3</code> attempts to access <code>x</code>, which is | ||
| 165 | not allowed! A closure<a href="#fn1" class="footnote-ref" id="fnref1" | ||
| 166 | role="doc-noteref"><sup>1</sup></a> however, can. If we are returning a | ||
| 167 | closure, our return type must be <code>impl Fn</code>, and not | ||
| 168 | <code>fn</code>. The difference between the <code>Fn</code> trait and | ||
| 169 | function pointers is beyond the scope of this post.</p> | ||
| 122 | <h3 id="refinement">Refinement</h3> | 170 | <h3 id="refinement">Refinement</h3> |
| 123 | <p>Armed with knowledge, we refine our expected output, this time, employing closures:</p> | 171 | <p>Armed with knowledge, we refine our expected output, this time, |
| 124 | <div class="sourceCode" id="cb8"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb8-1"><a href="#cb8-1" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add(x<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> <span class="dt">u32</span> <span class="op">{</span></span> | 172 | employing closures:</p> |
| 125 | <span id="cb8-2"><a href="#cb8-2" aria-hidden="true" tabindex="-1"></a> <span class="kw">return</span> <span class="kw">move</span> <span class="op">|</span>y<span class="op">|</span> <span class="kw">move</span> <span class="op">|</span>z<span class="op">|</span> x <span class="op">+</span> y <span class="op">+</span> z<span class="op">;</span></span> | 173 | <div class="sourceCode" id="cb8"><pre |
| 174 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb8-1"><a href="#cb8-1" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add(x<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> <span class="dt">u32</span> <span class="op">{</span></span> | ||
| 175 | <span id="cb8-2"><a href="#cb8-2" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> <span class="kw">move</span> <span class="op">|</span>y<span class="op">|</span> <span class="kw">move</span> <span class="op">|</span>z<span class="op">|</span> x <span class="op">+</span> y <span class="op">+</span> z<span class="op">;</span></span> | ||
| 126 | <span id="cb8-3"><a href="#cb8-3" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> | 176 | <span id="cb8-3"><a href="#cb8-3" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> |
| 127 | <p>Alas, that does not compile either! It errors out with the following message:</p> | 177 | <p>Alas, that does not compile either! It errors out with the following |
| 178 | message:</p> | ||
| 128 | <pre><code>error[E0562]: `impl Trait` not allowed outside of function | 179 | <pre><code>error[E0562]: `impl Trait` not allowed outside of function |
| 129 | and inherent method return types | 180 | and inherent method return types |
| 130 | --> src/main.rs:17:37 | 181 | --> src/main.rs:17:37 |
| @@ -132,21 +183,33 @@ and inherent method return types | |||
| 132 | | fn add(x: u32) -> impl Fn(u32) -> impl Fn(u32) -> u32 | 183 | | fn add(x: u32) -> impl Fn(u32) -> impl Fn(u32) -> u32 |
| 133 | | ^^^^^^^^^^^^^^^^^^^ | 184 | | ^^^^^^^^^^^^^^^^^^^ |
| 134 | </code></pre> | 185 | </code></pre> |
| 135 | <p>You are allowed to return an <code>impl Fn</code> 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.</p> | 186 | <p>You are allowed to return an <code>impl Fn</code> only inside a |
| 136 | <p>We are going to have to cheat a bit to fix this issue; with type aliases and a convenient nightly feature <a href="#fn2" class="footnote-ref" id="fnref2" role="doc-noteref"><sup>2</sup></a>:</p> | 187 | function. We are currently returning it from another return! Or at |
| 137 | <div class="sourceCode" id="cb10"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb10-1"><a href="#cb10-1" aria-hidden="true" tabindex="-1"></a><span class="at">#![</span>feature<span class="at">(</span>type_alias_impl_trait<span class="at">)]</span> <span class="co">// allows us to use `impl Fn` in type aliases!</span></span> | 188 | least, that was the most I could make out of the error message.</p> |
| 189 | <p>We are going to have to cheat a bit to fix this issue; with type | ||
| 190 | aliases and a convenient nightly feature <a href="#fn2" | ||
| 191 | class="footnote-ref" id="fnref2" | ||
| 192 | role="doc-noteref"><sup>2</sup></a>:</p> | ||
| 193 | <div class="sourceCode" id="cb10"><pre | ||
| 194 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb10-1"><a href="#cb10-1" aria-hidden="true" tabindex="-1"></a><span class="at">#![</span>feature<span class="at">(</span>type_alias_impl_trait<span class="at">)]</span> <span class="co">// allows us to use `impl Fn` in type aliases!</span></span> | ||
| 138 | <span id="cb10-2"><a href="#cb10-2" aria-hidden="true" tabindex="-1"></a></span> | 195 | <span id="cb10-2"><a href="#cb10-2" aria-hidden="true" tabindex="-1"></a></span> |
| 139 | <span id="cb10-3"><a href="#cb10-3" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> <span class="dt">u32</span><span class="op">;</span> <span class="co">// the return value when zero args are to be applied</span></span> | 196 | <span id="cb10-3"><a href="#cb10-3" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> <span class="dt">u32</span><span class="op">;</span> <span class="co">// the return value when zero args are to be applied</span></span> |
| 140 | <span id="cb10-4"><a href="#cb10-4" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> T0<span class="op">;</span> <span class="co">// the return value when one arg is to be applied</span></span> | 197 | <span id="cb10-4"><a href="#cb10-4" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> T0<span class="op">;</span> <span class="co">// the return value when one arg is to be applied</span></span> |
| 141 | <span id="cb10-5"><a href="#cb10-5" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T2 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> T1<span class="op">;</span> <span class="co">// the return value when two args are to be applied</span></span> | 198 | <span id="cb10-5"><a href="#cb10-5" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T2 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> T1<span class="op">;</span> <span class="co">// the return value when two args are to be applied</span></span> |
| 142 | <span id="cb10-6"><a href="#cb10-6" aria-hidden="true" tabindex="-1"></a></span> | 199 | <span id="cb10-6"><a href="#cb10-6" aria-hidden="true" tabindex="-1"></a></span> |
| 143 | <span id="cb10-7"><a href="#cb10-7" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add(x<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> T2 <span class="op">{</span></span> | 200 | <span id="cb10-7"><a href="#cb10-7" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add(x<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> T2 <span class="op">{</span></span> |
| 144 | <span id="cb10-8"><a href="#cb10-8" aria-hidden="true" tabindex="-1"></a> <span class="kw">return</span> <span class="kw">move</span> <span class="op">|</span>y<span class="op">|</span> <span class="kw">move</span> <span class="op">|</span>z<span class="op">|</span> x <span class="op">+</span> y <span class="op">+</span> z<span class="op">;</span></span> | 201 | <span id="cb10-8"><a href="#cb10-8" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> <span class="kw">move</span> <span class="op">|</span>y<span class="op">|</span> <span class="kw">move</span> <span class="op">|</span>z<span class="op">|</span> x <span class="op">+</span> y <span class="op">+</span> z<span class="op">;</span></span> |
| 145 | <span id="cb10-9"><a href="#cb10-9" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> | 202 | <span id="cb10-9"><a href="#cb10-9" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> |
| 146 | <p>Drop that into a cargo project, call <code>add(4)(5)(6)</code>, cross your fingers, and run <code>cargo +nightly run</code>. You should see a 15 unless you forgot to print it!</p> | 203 | <p>Drop that into a cargo project, call <code>add(4)(5)(6)</code>, cross |
| 204 | your fingers, and run <code>cargo +nightly run</code>. You should see a | ||
| 205 | 15 unless you forgot to print it!</p> | ||
| 147 | <h3 id="the-in-betweens">The In-Betweens</h3> | 206 | <h3 id="the-in-betweens">The In-Betweens</h3> |
| 148 | <p>Let us write the magical bits that take us from function to curried function.</p> | 207 | <p>Let us write the magical bits that take us from function to curried |
| 149 | <p>Initialize your workspace with <code>cargo new --lib currying</code>. Proc-macro crates are libraries with exactly one export, the macro itself. Add a <code>tests</code> directory to your crate root. Your directory should look something like this:</p> | 208 | function.</p> |
| 209 | <p>Initialize your workspace with <code>cargo new --lib currying</code>. | ||
| 210 | Proc-macro crates are libraries with exactly one export, the macro | ||
| 211 | itself. Add a <code>tests</code> directory to your crate root. Your | ||
| 212 | directory should look something like this:</p> | ||
| 150 | <pre><code>. | 213 | <pre><code>. |
| 151 | ├── Cargo.toml | 214 | ├── Cargo.toml |
| 152 | ├── src | 215 | ├── src |
| @@ -156,9 +219,11 @@ and inherent method return types | |||
| 156 | <h4 id="dependencies">Dependencies</h4> | 219 | <h4 id="dependencies">Dependencies</h4> |
| 157 | <p>We will be using a total of 3 external crates:</p> | 220 | <p>We will be using a total of 3 external crates:</p> |
| 158 | <ul> | 221 | <ul> |
| 159 | <li><a href="https://docs.rs/proc-macro2/1.0.12/proc_macro2/">proc_macro2</a></li> | 222 | <li><a |
| 223 | href="https://docs.rs/proc-macro2/1.0.12/proc_macro2/">proc_macro2</a></li> | ||
| 160 | <li><a href="https://docs.rs/syn/1.0.18/syn/index.html">syn</a></li> | 224 | <li><a href="https://docs.rs/syn/1.0.18/syn/index.html">syn</a></li> |
| 161 | <li><a href="https://docs.rs/quote/1.0.4/quote/index.html">quote</a></li> | 225 | <li><a |
| 226 | href="https://docs.rs/quote/1.0.4/quote/index.html">quote</a></li> | ||
| 162 | </ul> | 227 | </ul> |
| 163 | <p>Here’s a sample <code>Cargo.toml</code>:</p> | 228 | <p>Here’s a sample <code>Cargo.toml</code>:</p> |
| 164 | <pre><code># Cargo.toml | 229 | <pre><code># Cargo.toml |
| @@ -173,10 +238,12 @@ features = ["full"] | |||
| 173 | 238 | ||
| 174 | [lib] | 239 | [lib] |
| 175 | proc-macro = true # this is important!</code></pre> | 240 | proc-macro = true # this is important!</code></pre> |
| 176 | <p>We will be using an external <code>proc-macro2</code> crate as well as an internal <code>proc-macro</code> crate. Not confusing at all!</p> | 241 | <p>We will be using an external <code>proc-macro2</code> crate as well |
| 242 | as an internal <code>proc-macro</code> crate. Not confusing at all!</p> | ||
| 177 | <h4 id="the-attribute-macro">The attribute macro</h4> | 243 | <h4 id="the-attribute-macro">The attribute macro</h4> |
| 178 | <p>Drop this into <code>src/lib.rs</code>, to get the ball rolling.</p> | 244 | <p>Drop this into <code>src/lib.rs</code>, to get the ball rolling.</p> |
| 179 | <div class="sourceCode" id="cb13"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb13-1"><a href="#cb13-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | 245 | <div class="sourceCode" id="cb13"><pre |
| 246 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb13-1"><a href="#cb13-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | ||
| 180 | <span id="cb13-2"><a href="#cb13-2" aria-hidden="true" tabindex="-1"></a></span> | 247 | <span id="cb13-2"><a href="#cb13-2" aria-hidden="true" tabindex="-1"></a></span> |
| 181 | <span id="cb13-3"><a href="#cb13-3" aria-hidden="true" tabindex="-1"></a><span class="kw">use</span> <span class="pp">proc_macro::</span>TokenStream<span class="op">;</span> <span class="co">// 1</span></span> | 248 | <span id="cb13-3"><a href="#cb13-3" aria-hidden="true" tabindex="-1"></a><span class="kw">use</span> <span class="pp">proc_macro::</span>TokenStream<span class="op">;</span> <span class="co">// 1</span></span> |
| 182 | <span id="cb13-4"><a href="#cb13-4" aria-hidden="true" tabindex="-1"></a><span class="kw">use</span> <span class="pp">quote::</span>quote<span class="op">;</span></span> | 249 | <span id="cb13-4"><a href="#cb13-4" aria-hidden="true" tabindex="-1"></a><span class="kw">use</span> <span class="pp">quote::</span>quote<span class="op">;</span></span> |
| @@ -190,17 +257,49 @@ proc-macro = true # this is important!</code></pre> | |||
| 190 | <span id="cb13-12"><a href="#cb13-12" aria-hidden="true" tabindex="-1"></a></span> | 257 | <span id="cb13-12"><a href="#cb13-12" aria-hidden="true" tabindex="-1"></a></span> |
| 191 | <span id="cb13-13"><a href="#cb13-13" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> generate_curry(parsed<span class="op">:</span> ItemFn) <span class="op">-></span> <span class="pp">proc_macro2::</span>TokenStream <span class="op">{}</span></span></code></pre></div> | 258 | <span id="cb13-13"><a href="#cb13-13" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> generate_curry(parsed<span class="op">:</span> ItemFn) <span class="op">-></span> <span class="pp">proc_macro2::</span>TokenStream <span class="op">{}</span></span></code></pre></div> |
| 192 | <p><strong>1. Imports</strong></p> | 259 | <p><strong>1. Imports</strong></p> |
| 193 | <p>A <code>Tokenstream</code> holds (hopefully valid) Rust code, this is the type of our input and output. Note that we are importing this type from <code>proc_macro</code> and not <code>proc_macro2</code>.</p> | 260 | <p>A <code>Tokenstream</code> holds (hopefully valid) Rust code, this is |
| 194 | <p><code>quote!</code> from the <code>quote</code> crate is a macro that allows us to quickly produce <code>TokenStream</code>s. Much like the LISP <code>quote</code> procedure, you can use the <code>quote!</code> macro for symbolic transformations.</p> | 261 | the type of our input and output. Note that we are importing this type |
| 195 | <p><code>ItemFn</code> from the <code>syn</code> crate holds the parsed <code>TokenStream</code> of a Rust function. <code>parse_macro_input!</code> is a helper macro provided by <code>syn</code>.</p> | 262 | from <code>proc_macro</code> and not <code>proc_macro2</code>.</p> |
| 263 | <p><code>quote!</code> from the <code>quote</code> crate is a macro that | ||
| 264 | allows us to quickly produce <code>TokenStream</code>s. Much like the | ||
| 265 | LISP <code>quote</code> procedure, you can use the <code>quote!</code> | ||
| 266 | macro for symbolic transformations.</p> | ||
| 267 | <p><code>ItemFn</code> from the <code>syn</code> crate holds the parsed | ||
| 268 | <code>TokenStream</code> of a Rust function. | ||
| 269 | <code>parse_macro_input!</code> is a helper macro provided by | ||
| 270 | <code>syn</code>.</p> | ||
| 196 | <p><strong>2. The lone export</strong></p> | 271 | <p><strong>2. The lone export</strong></p> |
| 197 | <p>Annotate the only <code>pub</code> of our crate with <code>#[proc_macro_attribute]</code>. This tells rustc that <code>curry</code> is a procedural macro, and allows us to use it as <code>#[crate_name::curry]</code> in other crates. Note the signature of the <code>curry</code> function. <code>_attr</code> is the <code>TokenStream</code> representing the attribute itself, <code>item</code> refers to the thing we slapped our macro into, in this case a function (like <code>add</code>). The return value is a modified <code>TokenStream</code>, this will contain our curried version of <code>add</code>.</p> | 272 | <p>Annotate the only <code>pub</code> of our crate with |
| 273 | <code>#[proc_macro_attribute]</code>. This tells rustc that | ||
| 274 | <code>curry</code> is a procedural macro, and allows us to use it as | ||
| 275 | <code>#[crate_name::curry]</code> in other crates. Note the signature of | ||
| 276 | the <code>curry</code> function. <code>_attr</code> is the | ||
| 277 | <code>TokenStream</code> representing the attribute itself, | ||
| 278 | <code>item</code> refers to the thing we slapped our macro into, in this | ||
| 279 | case a function (like <code>add</code>). The return value is a modified | ||
| 280 | <code>TokenStream</code>, this will contain our curried version of | ||
| 281 | <code>add</code>.</p> | ||
| 198 | <p><strong>3. The helper macro</strong></p> | 282 | <p><strong>3. The helper macro</strong></p> |
| 199 | <p>A <code>TokenStream</code> is a little hard to work with, which is why we have the <code>syn</code> crate, which provides types to represent Rust tokens. An <code>RArrow</code> struct to represent the return arrow on a function and so on. One of those types is <code>ItemFn</code>, that represents an entire Rust function. The <code>parse_macro_input!</code> automatically puts the input to our macro into an <code>ItemFn</code>. What a gentleman!</p> | 283 | <p>A <code>TokenStream</code> is a little hard to work with, which is |
| 284 | why we have the <code>syn</code> crate, which provides types to | ||
| 285 | represent Rust tokens. An <code>RArrow</code> struct to represent the | ||
| 286 | return arrow on a function and so on. One of those types is | ||
| 287 | <code>ItemFn</code>, that represents an entire Rust function. The | ||
| 288 | <code>parse_macro_input!</code> automatically puts the input to our | ||
| 289 | macro into an <code>ItemFn</code>. What a gentleman!</p> | ||
| 200 | <p><strong>4. Returning <code>TokenStream</code>s </strong></p> | 290 | <p><strong>4. Returning <code>TokenStream</code>s </strong></p> |
| 201 | <p>We haven’t filled in <code>generate_curry</code> yet, but we can see that it returns a <code>proc_macro2::TokenStream</code> and not a <code>proc_macro::TokenStream</code>, so drop a <code>.into()</code> to convert it.</p> | 291 | <p>We haven’t filled in <code>generate_curry</code> yet, but we can see |
| 202 | <p>Lets move on, and fill in <code>generate_curry</code>, I would suggest keeping the documentation for <a href="https://docs.rs/syn/1.0.19/syn/struct.ItemFn.html"><code>syn::ItemFn</code></a> and <a href="https://docs.rs/syn/1.0.19/syn/struct.Signature.html"><code>syn::Signature</code></a> open.</p> | 292 | that it returns a <code>proc_macro2::TokenStream</code> and not a |
| 203 | <div class="sourceCode" id="cb14"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb14-1"><a href="#cb14-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | 293 | <code>proc_macro::TokenStream</code>, so drop a <code>.into()</code> to |
| 294 | convert it.</p> | ||
| 295 | <p>Lets move on, and fill in <code>generate_curry</code>, I would | ||
| 296 | suggest keeping the documentation for <a | ||
| 297 | href="https://docs.rs/syn/1.0.19/syn/struct.ItemFn.html"><code>syn::ItemFn</code></a> | ||
| 298 | and <a | ||
| 299 | href="https://docs.rs/syn/1.0.19/syn/struct.Signature.html"><code>syn::Signature</code></a> | ||
| 300 | open.</p> | ||
| 301 | <div class="sourceCode" id="cb14"><pre | ||
| 302 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb14-1"><a href="#cb14-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | ||
| 204 | <span id="cb14-2"><a href="#cb14-2" aria-hidden="true" tabindex="-1"></a></span> | 303 | <span id="cb14-2"><a href="#cb14-2" aria-hidden="true" tabindex="-1"></a></span> |
| 205 | <span id="cb14-3"><a href="#cb14-3" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> generate_curry(parsed<span class="op">:</span> ItemFn) <span class="op">-></span> <span class="pp">proc_macro2::</span>TokenStream <span class="op">{</span></span> | 304 | <span id="cb14-3"><a href="#cb14-3" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> generate_curry(parsed<span class="op">:</span> ItemFn) <span class="op">-></span> <span class="pp">proc_macro2::</span>TokenStream <span class="op">{</span></span> |
| 206 | <span id="cb14-4"><a href="#cb14-4" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> fn_body <span class="op">=</span> parsed<span class="op">.</span>block<span class="op">;</span> <span class="co">// function body</span></span> | 305 | <span id="cb14-4"><a href="#cb14-4" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> fn_body <span class="op">=</span> parsed<span class="op">.</span>block<span class="op">;</span> <span class="co">// function body</span></span> |
| @@ -210,7 +309,9 @@ proc-macro = true # this is important!</code></pre> | |||
| 210 | <span id="cb14-8"><a href="#cb14-8" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> fn_args <span class="op">=</span> sig<span class="op">.</span>inputs<span class="op">;</span> <span class="co">// comma separated args</span></span> | 309 | <span id="cb14-8"><a href="#cb14-8" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> fn_args <span class="op">=</span> sig<span class="op">.</span>inputs<span class="op">;</span> <span class="co">// comma separated args</span></span> |
| 211 | <span id="cb14-9"><a href="#cb14-9" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> fn_return_type <span class="op">=</span> sig<span class="op">.</span>output<span class="op">;</span> <span class="co">// return type</span></span> | 310 | <span id="cb14-9"><a href="#cb14-9" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> fn_return_type <span class="op">=</span> sig<span class="op">.</span>output<span class="op">;</span> <span class="co">// return type</span></span> |
| 212 | <span id="cb14-10"><a href="#cb14-10" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> | 311 | <span id="cb14-10"><a href="#cb14-10" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> |
| 213 | <p>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 <code>syn::Signature</code> can tell us about a function:</p> | 312 | <p>We are simply extracting the bits of the function, we will be reusing |
| 313 | the original function’s visibility and name. Take a look at what | ||
| 314 | <code>syn::Signature</code> can tell us about a function:</p> | ||
| 214 | <pre><code> .-- syn::Ident (ident) | 315 | <pre><code> .-- syn::Ident (ident) |
| 215 | / | 316 | / |
| 216 | fn add(x: u32, y: u32) -> u32 | 317 | fn add(x: u32, y: u32) -> u32 |
| @@ -220,42 +321,77 @@ syn::token::Fn --' / \ (output) | |||
| 220 | Punctuated<FnArg, Comma> (inputs)</code></pre> | 321 | Punctuated<FnArg, Comma> (inputs)</code></pre> |
| 221 | <p>Enough analysis, lets produce our first bit of Rust code.</p> | 322 | <p>Enough analysis, lets produce our first bit of Rust code.</p> |
| 222 | <h4 id="function-body">Function Body</h4> | 323 | <h4 id="function-body">Function Body</h4> |
| 223 | <p>Recall that the body of a curried <code>add</code> should look like this:</p> | 324 | <p>Recall that the body of a curried <code>add</code> should look like |
| 224 | <div class="sourceCode" id="cb16"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb16-1"><a href="#cb16-1" aria-hidden="true" tabindex="-1"></a><span class="kw">return</span> <span class="kw">move</span> <span class="op">|</span>y<span class="op">|</span> <span class="kw">move</span> <span class="op">|</span>z<span class="op">|</span> x <span class="op">+</span> y <span class="op">+</span> z<span class="op">;</span></span></code></pre></div> | 325 | this:</p> |
| 326 | <div class="sourceCode" id="cb16"><pre | ||
| 327 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb16-1"><a href="#cb16-1" aria-hidden="true" tabindex="-1"></a><span class="cf">return</span> <span class="kw">move</span> <span class="op">|</span>y<span class="op">|</span> <span class="kw">move</span> <span class="op">|</span>z<span class="op">|</span> x <span class="op">+</span> y <span class="op">+</span> z<span class="op">;</span></span></code></pre></div> | ||
| 225 | <p>And in general:</p> | 328 | <p>And in general:</p> |
| 226 | <div class="sourceCode" id="cb17"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb17-1"><a href="#cb17-1" aria-hidden="true" tabindex="-1"></a><span class="kw">return</span> <span class="kw">move</span> <span class="op">|</span>arg2<span class="op">|</span> <span class="kw">move</span> <span class="op">|</span>arg3<span class="op">|</span> <span class="op">...</span> <span class="op">|</span>argN<span class="op">|</span> <span class="op"><</span>function body here<span class="op">></span></span></code></pre></div> | 329 | <div class="sourceCode" id="cb17"><pre |
| 227 | <p>We already have the function’s body, provided by <code>fn_body</code>, in our <code>generate_curry</code> function. All that’s left to add is the <code>move |arg2| move |arg3| ...</code> stuff, for which we need to extract the argument identifiers (doc: <a href="https://docs.rs/syn/1.0.18/syn/punctuated/struct.Punctuated.html">Punctuated</a>, <a href="https://docs.rs/syn/1.0.18/syn/enum.FnArg.html">FnArg</a>, <a href="https://docs.rs/syn/1.0.18/syn/struct.PatType.html">PatType</a>):</p> | 330 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb17-1"><a href="#cb17-1" aria-hidden="true" tabindex="-1"></a><span class="cf">return</span> <span class="kw">move</span> <span class="op">|</span>arg2<span class="op">|</span> <span class="kw">move</span> <span class="op">|</span>arg3<span class="op">|</span> <span class="op">...</span> <span class="op">|</span>argN<span class="op">|</span> <span class="op"><</span>function body here<span class="op">></span></span></code></pre></div> |
| 228 | <div class="sourceCode" id="cb18"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb18-1"><a href="#cb18-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | 331 | <p>We already have the function’s body, provided by |
| 332 | <code>fn_body</code>, in our <code>generate_curry</code> function. All | ||
| 333 | that’s left to add is the <code>move |arg2| move |arg3| ...</code> | ||
| 334 | stuff, for which we need to extract the argument identifiers (doc: <a | ||
| 335 | href="https://docs.rs/syn/1.0.18/syn/punctuated/struct.Punctuated.html">Punctuated</a>, | ||
| 336 | <a href="https://docs.rs/syn/1.0.18/syn/enum.FnArg.html">FnArg</a>, <a | ||
| 337 | href="https://docs.rs/syn/1.0.18/syn/struct.PatType.html">PatType</a>):</p> | ||
| 338 | <div class="sourceCode" id="cb18"><pre | ||
| 339 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb18-1"><a href="#cb18-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | ||
| 229 | <span id="cb18-2"><a href="#cb18-2" aria-hidden="true" tabindex="-1"></a><span class="kw">use</span> <span class="pp">syn::punctuated::</span>Punctuated<span class="op">;</span></span> | 340 | <span id="cb18-2"><a href="#cb18-2" aria-hidden="true" tabindex="-1"></a><span class="kw">use</span> <span class="pp">syn::punctuated::</span>Punctuated<span class="op">;</span></span> |
| 230 | <span id="cb18-3"><a href="#cb18-3" aria-hidden="true" tabindex="-1"></a><span class="kw">use</span> <span class="pp">syn::</span><span class="op">{</span>parse_macro_input<span class="op">,</span> FnArg<span class="op">,</span> Pat<span class="op">,</span> ItemFn<span class="op">,</span> Block<span class="op">};</span></span> | 341 | <span id="cb18-3"><a href="#cb18-3" aria-hidden="true" tabindex="-1"></a><span class="kw">use</span> <span class="pp">syn::</span><span class="op">{</span>parse_macro_input<span class="op">,</span> FnArg<span class="op">,</span> Pat<span class="op">,</span> ItemFn<span class="op">,</span> Block<span class="op">};</span></span> |
| 231 | <span id="cb18-4"><a href="#cb18-4" aria-hidden="true" tabindex="-1"></a></span> | 342 | <span id="cb18-4"><a href="#cb18-4" aria-hidden="true" tabindex="-1"></a></span> |
| 232 | <span id="cb18-5"><a href="#cb18-5" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> extract_arg_idents(fn_args<span class="op">:</span> Punctuated<span class="op"><</span>FnArg<span class="op">,</span> <span class="pp">syn::token::</span>Comma<span class="op">></span>) <span class="op">-></span> <span class="dt">Vec</span><span class="op"><</span><span class="dt">Box</span><span class="op"><</span>Pat<span class="op">>></span> <span class="op">{</span> </span> | 343 | <span id="cb18-5"><a href="#cb18-5" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> extract_arg_idents(fn_args<span class="op">:</span> Punctuated<span class="op"><</span>FnArg<span class="op">,</span> <span class="pp">syn::token::</span>Comma<span class="op">></span>) <span class="op">-></span> <span class="dt">Vec</span><span class="op"><</span><span class="dt">Box</span><span class="op"><</span>Pat<span class="op">>></span> <span class="op">{</span> </span> |
| 233 | <span id="cb18-6"><a href="#cb18-6" aria-hidden="true" tabindex="-1"></a> <span class="kw">return</span> fn_args<span class="op">.</span>into_iter()<span class="op">.</span>map(extract_arg_pat)<span class="op">.</span><span class="pp">collect::</span><span class="op"><</span><span class="dt">Vec</span><span class="op"><</span>_<span class="op">>></span>()<span class="op">;</span></span> | 344 | <span id="cb18-6"><a href="#cb18-6" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> fn_args<span class="op">.</span>into_iter()<span class="op">.</span>map(extract_arg_pat)<span class="op">.</span><span class="pp">collect::</span><span class="op"><</span><span class="dt">Vec</span><span class="op"><</span>_<span class="op">>></span>()<span class="op">;</span></span> |
| 234 | <span id="cb18-7"><a href="#cb18-7" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> | 345 | <span id="cb18-7"><a href="#cb18-7" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> |
| 235 | <p>Alright, so we are iterating over function args (<code>Punctuated</code> is a collection that you can iterate over) and mapping an <code>extract_arg_pat</code> to every item. What’s <code>extract_arg_pat</code>?</p> | 346 | <p>Alright, so we are iterating over function args |
| 236 | <div class="sourceCode" id="cb19"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb19-1"><a href="#cb19-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | 347 | (<code>Punctuated</code> is a collection that you can iterate over) and |
| 348 | mapping an <code>extract_arg_pat</code> to every item. What’s | ||
| 349 | <code>extract_arg_pat</code>?</p> | ||
| 350 | <div class="sourceCode" id="cb19"><pre | ||
| 351 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb19-1"><a href="#cb19-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | ||
| 237 | <span id="cb19-2"><a href="#cb19-2" aria-hidden="true" tabindex="-1"></a></span> | 352 | <span id="cb19-2"><a href="#cb19-2" aria-hidden="true" tabindex="-1"></a></span> |
| 238 | <span id="cb19-3"><a href="#cb19-3" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> extract_arg_pat(a<span class="op">:</span> FnArg) <span class="op">-></span> <span class="dt">Box</span><span class="op"><</span>Pat<span class="op">></span> <span class="op">{</span></span> | 353 | <span id="cb19-3"><a href="#cb19-3" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> extract_arg_pat(a<span class="op">:</span> FnArg) <span class="op">-></span> <span class="dt">Box</span><span class="op"><</span>Pat<span class="op">></span> <span class="op">{</span></span> |
| 239 | <span id="cb19-4"><a href="#cb19-4" aria-hidden="true" tabindex="-1"></a> <span class="kw">match</span> a <span class="op">{</span></span> | 354 | <span id="cb19-4"><a href="#cb19-4" aria-hidden="true" tabindex="-1"></a> <span class="cf">match</span> a <span class="op">{</span></span> |
| 240 | <span id="cb19-5"><a href="#cb19-5" aria-hidden="true" tabindex="-1"></a> <span class="pp">FnArg::</span>Typed(p) <span class="op">=></span> p<span class="op">.</span>pat<span class="op">,</span></span> | 355 | <span id="cb19-5"><a href="#cb19-5" aria-hidden="true" tabindex="-1"></a> <span class="pp">FnArg::</span>Typed(p) <span class="op">=></span> p<span class="op">.</span>pat<span class="op">,</span></span> |
| 241 | <span id="cb19-6"><a href="#cb19-6" aria-hidden="true" tabindex="-1"></a> _ <span class="op">=></span> <span class="pp">panic!</span>(<span class="st">"Not supported on types with `self`!"</span>)<span class="op">,</span></span> | 356 | <span id="cb19-6"><a href="#cb19-6" aria-hidden="true" tabindex="-1"></a> _ <span class="op">=></span> <span class="pp">panic!</span>(<span class="st">"Not supported on types with `self`!"</span>)<span class="op">,</span></span> |
| 242 | <span id="cb19-7"><a href="#cb19-7" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> | 357 | <span id="cb19-7"><a href="#cb19-7" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> |
| 243 | <span id="cb19-8"><a href="#cb19-8" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> | 358 | <span id="cb19-8"><a href="#cb19-8" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> |
| 244 | <p><code>FnArg</code> is an enum type as you might have guessed. The <code>Typed</code> variant encompasses args that are written as <code>name: type</code> and the other variant, <code>Reciever</code> refers to <code>self</code> types. Ignore those for now, keep it simple.</p> | 359 | <p><code>FnArg</code> is an enum type as you might have guessed. The |
| 245 | <p>Every <code>FnArg::Typed</code> value contains a <code>pat</code>, which is in essence, the name of the argument. The type of the arg is accessible via <code>p.ty</code> (we will be using this later).</p> | 360 | <code>Typed</code> variant encompasses args that are written as |
| 246 | <p>With that done, we should be able to write the codegen for the function body:</p> | 361 | <code>name: type</code> and the other variant, <code>Reciever</code> |
| 247 | <div class="sourceCode" id="cb20"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb20-1"><a href="#cb20-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | 362 | refers to <code>self</code> types. Ignore those for now, keep it |
| 363 | simple.</p> | ||
| 364 | <p>Every <code>FnArg::Typed</code> value contains a <code>pat</code>, | ||
| 365 | which is in essence, the name of the argument. The type of the arg is | ||
| 366 | accessible via <code>p.ty</code> (we will be using this later).</p> | ||
| 367 | <p>With that done, we should be able to write the codegen for the | ||
| 368 | function body:</p> | ||
| 369 | <div class="sourceCode" id="cb20"><pre | ||
| 370 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb20-1"><a href="#cb20-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | ||
| 248 | <span id="cb20-2"><a href="#cb20-2" aria-hidden="true" tabindex="-1"></a></span> | 371 | <span id="cb20-2"><a href="#cb20-2" aria-hidden="true" tabindex="-1"></a></span> |
| 249 | <span id="cb20-3"><a href="#cb20-3" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> generate_body(fn_args<span class="op">:</span> <span class="op">&</span>[<span class="dt">Box</span><span class="op"><</span>Pat<span class="op">></span>]<span class="op">,</span> body<span class="op">:</span> <span class="dt">Box</span><span class="op"><</span>Block<span class="op">></span>) <span class="op">-></span> <span class="pp">proc_macro2::</span>TokenStream <span class="op">{</span></span> | 372 | <span id="cb20-3"><a href="#cb20-3" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> generate_body(fn_args<span class="op">:</span> <span class="op">&</span>[<span class="dt">Box</span><span class="op"><</span>Pat<span class="op">></span>]<span class="op">,</span> body<span class="op">:</span> <span class="dt">Box</span><span class="op"><</span>Block<span class="op">></span>) <span class="op">-></span> <span class="pp">proc_macro2::</span>TokenStream <span class="op">{</span></span> |
| 250 | <span id="cb20-4"><a href="#cb20-4" aria-hidden="true" tabindex="-1"></a> <span class="pp">quote!</span> <span class="op">{</span></span> | 373 | <span id="cb20-4"><a href="#cb20-4" aria-hidden="true" tabindex="-1"></a> <span class="pp">quote!</span> <span class="op">{</span></span> |
| 251 | <span id="cb20-5"><a href="#cb20-5" aria-hidden="true" tabindex="-1"></a> <span class="kw">return</span> #( <span class="kw">move</span> <span class="op">|</span>#fn_args<span class="op">|</span> )<span class="op">*</span> #body</span> | 374 | <span id="cb20-5"><a href="#cb20-5" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> #( <span class="kw">move</span> <span class="op">|</span>#fn_args<span class="op">|</span> )<span class="op">*</span> #body</span> |
| 252 | <span id="cb20-6"><a href="#cb20-6" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> | 375 | <span id="cb20-6"><a href="#cb20-6" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> |
| 253 | <span id="cb20-7"><a href="#cb20-7" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> | 376 | <span id="cb20-7"><a href="#cb20-7" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> |
| 254 | <p>That is some scary looking syntax! Allow me to explain. The <code>quote!{ ... }</code> returns a <code>proc_macro2::TokenStream</code>, if we wrote <code>quote!{ let x = 1 + 2; }</code>, it wouldn’t create a new variable <code>x</code> with value 3, it would literally produce a stream of tokens with that expression.</p> | 377 | <p>That is some scary looking syntax! Allow me to explain. The |
| 255 | <p>The <code>#</code> enables variable interpolation. <code>#body</code> will look for <code>body</code> in the current scope, take its value, and insert it in the returned <code>TokenStream</code>. Kinda like quasi quoting in LISPs, you have written one.</p> | 378 | <code>quote!{ ... }</code> returns a |
| 256 | <p>What about <code>#( move |#fn_args| )*</code>? That is repetition. <code>quote</code> iterates through <code>fn_args</code>, and drops a <code>move</code> behind each one, it then places pipes (<code>|</code>), around it.</p> | 379 | <code>proc_macro2::TokenStream</code>, if we wrote |
| 257 | <p>Let us test our first bit of codegen! Modify <code>generate_curry</code> like so:</p> | 380 | <code>quote!{ let x = 1 + 2; }</code>, it wouldn’t create a new variable |
| 258 | <div class="sourceCode" id="cb21"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb21-1"><a href="#cb21-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | 381 | <code>x</code> with value 3, it would literally produce a stream of |
| 382 | tokens with that expression.</p> | ||
| 383 | <p>The <code>#</code> enables variable interpolation. <code>#body</code> | ||
| 384 | will look for <code>body</code> in the current scope, take its value, | ||
| 385 | and insert it in the returned <code>TokenStream</code>. Kinda like quasi | ||
| 386 | quoting in LISPs, you have written one.</p> | ||
| 387 | <p>What about <code>#( move |#fn_args| )*</code>? That is repetition. | ||
| 388 | <code>quote</code> iterates through <code>fn_args</code>, and drops a | ||
| 389 | <code>move</code> behind each one, it then places pipes | ||
| 390 | (<code>|</code>), around it.</p> | ||
| 391 | <p>Let us test our first bit of codegen! Modify | ||
| 392 | <code>generate_curry</code> like so:</p> | ||
| 393 | <div class="sourceCode" id="cb21"><pre | ||
| 394 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb21-1"><a href="#cb21-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | ||
| 259 | <span id="cb21-2"><a href="#cb21-2" aria-hidden="true" tabindex="-1"></a></span> | 395 | <span id="cb21-2"><a href="#cb21-2" aria-hidden="true" tabindex="-1"></a></span> |
| 260 | <span id="cb21-3"><a href="#cb21-3" aria-hidden="true" tabindex="-1"></a> <span class="kw">fn</span> generate_curry(parsed<span class="op">:</span> ItemFn) <span class="op">-></span> TokenStream <span class="op">{</span></span> | 396 | <span id="cb21-3"><a href="#cb21-3" aria-hidden="true" tabindex="-1"></a> <span class="kw">fn</span> generate_curry(parsed<span class="op">:</span> ItemFn) <span class="op">-></span> TokenStream <span class="op">{</span></span> |
| 261 | <span id="cb21-4"><a href="#cb21-4" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> fn_body <span class="op">=</span> parsed<span class="op">.</span>block<span class="op">;</span></span> | 397 | <span id="cb21-4"><a href="#cb21-4" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> fn_body <span class="op">=</span> parsed<span class="op">.</span>block<span class="op">;</span></span> |
| @@ -272,10 +408,11 @@ syn::token::Fn --' / \ (output) | |||
| 272 | <span id="cb21-15"><a href="#cb21-15" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> <span class="kw">let</span> curried_body <span class="op">=</span> generate_body(<span class="op">&</span>arg_idents[<span class="dv">1</span><span class="op">..</span>]<span class="op">,</span> fn_body<span class="op">.</span>clone())<span class="op">;</span></span> | 408 | <span id="cb21-15"><a href="#cb21-15" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> <span class="kw">let</span> curried_body <span class="op">=</span> generate_body(<span class="op">&</span>arg_idents[<span class="dv">1</span><span class="op">..</span>]<span class="op">,</span> fn_body<span class="op">.</span>clone())<span class="op">;</span></span> |
| 273 | <span id="cb21-16"><a href="#cb21-16" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> <span class="pp">println!</span>(<span class="st">"{}"</span><span class="op">,</span> curried_body)<span class="op">;</span></span> | 409 | <span id="cb21-16"><a href="#cb21-16" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> <span class="pp">println!</span>(<span class="st">"{}"</span><span class="op">,</span> curried_body)<span class="op">;</span></span> |
| 274 | <span id="cb21-17"><a href="#cb21-17" aria-hidden="true" tabindex="-1"></a></span> | 410 | <span id="cb21-17"><a href="#cb21-17" aria-hidden="true" tabindex="-1"></a></span> |
| 275 | <span id="cb21-18"><a href="#cb21-18" aria-hidden="true" tabindex="-1"></a> <span class="kw">return</span> <span class="pp">TokenStream::</span>new()<span class="op">;</span></span> | 411 | <span id="cb21-18"><a href="#cb21-18" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> <span class="pp">TokenStream::</span>new()<span class="op">;</span></span> |
| 276 | <span id="cb21-19"><a href="#cb21-19" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span></code></pre></div> | 412 | <span id="cb21-19"><a href="#cb21-19" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span></code></pre></div> |
| 277 | <p>Add a little test to <code>tests/</code>:</p> | 413 | <p>Add a little test to <code>tests/</code>:</p> |
| 278 | <div class="sourceCode" id="cb22"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb22-1"><a href="#cb22-1" aria-hidden="true" tabindex="-1"></a><span class="co">// tests/smoke.rs</span></span> | 414 | <div class="sourceCode" id="cb22"><pre |
| 415 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb22-1"><a href="#cb22-1" aria-hidden="true" tabindex="-1"></a><span class="co">// tests/smoke.rs</span></span> | ||
| 279 | <span id="cb22-2"><a href="#cb22-2" aria-hidden="true" tabindex="-1"></a></span> | 416 | <span id="cb22-2"><a href="#cb22-2" aria-hidden="true" tabindex="-1"></a></span> |
| 280 | <span id="cb22-3"><a href="#cb22-3" aria-hidden="true" tabindex="-1"></a><span class="at">#[</span><span class="pp">currying::</span>curry<span class="at">]</span></span> | 417 | <span id="cb22-3"><a href="#cb22-3" aria-hidden="true" tabindex="-1"></a><span class="at">#[</span><span class="pp">currying::</span>curry<span class="at">]</span></span> |
| 281 | <span id="cb22-4"><a href="#cb22-4" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add(x<span class="op">:</span> <span class="dt">u32</span><span class="op">,</span> y<span class="op">:</span> <span class="dt">u32</span><span class="op">,</span> z<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> <span class="dt">u32</span> <span class="op">{</span></span> | 418 | <span id="cb22-4"><a href="#cb22-4" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add(x<span class="op">:</span> <span class="dt">u32</span><span class="op">,</span> y<span class="op">:</span> <span class="dt">u32</span><span class="op">,</span> z<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> <span class="dt">u32</span> <span class="op">{</span></span> |
| @@ -286,17 +423,23 @@ syn::token::Fn --' / \ (output) | |||
| 286 | <span id="cb22-9"><a href="#cb22-9" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> works() <span class="op">{</span></span> | 423 | <span id="cb22-9"><a href="#cb22-9" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> works() <span class="op">{</span></span> |
| 287 | <span id="cb22-10"><a href="#cb22-10" aria-hidden="true" tabindex="-1"></a> <span class="pp">assert!</span>(<span class="cn">true</span>)<span class="op">;</span></span> | 424 | <span id="cb22-10"><a href="#cb22-10" aria-hidden="true" tabindex="-1"></a> <span class="pp">assert!</span>(<span class="cn">true</span>)<span class="op">;</span></span> |
| 288 | <span id="cb22-11"><a href="#cb22-11" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> | 425 | <span id="cb22-11"><a href="#cb22-11" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> |
| 289 | <p>You should find something like this in the output of <code>cargo test</code>:</p> | 426 | <p>You should find something like this in the output of |
| 427 | <code>cargo test</code>:</p> | ||
| 290 | <pre><code>return move | y | move | z | { x + y + z }</code></pre> | 428 | <pre><code>return move | y | move | z | { x + y + z }</code></pre> |
| 291 | <p>Glorious <code>println!</code> debugging!</p> | 429 | <p>Glorious <code>println!</code> debugging!</p> |
| 292 | <h4 id="function-signature">Function signature</h4> | 430 | <h4 id="function-signature">Function signature</h4> |
| 293 | <p>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!</p> | 431 | <p>This section gets into the more complicated bits of the macro, |
| 294 | <p>Recall what our generated type aliases should look like, for our <code>add</code> function:</p> | 432 | generating type aliases and the function signature. By the end of this |
| 295 | <div class="sourceCode" id="cb24"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb24-1"><a href="#cb24-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> <span class="dt">u32</span><span class="op">;</span></span> | 433 | section, we should have a full working auto-currying macro!</p> |
| 434 | <p>Recall what our generated type aliases should look like, for our | ||
| 435 | <code>add</code> function:</p> | ||
| 436 | <div class="sourceCode" id="cb24"><pre | ||
| 437 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb24-1"><a href="#cb24-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> <span class="dt">u32</span><span class="op">;</span></span> | ||
| 296 | <span id="cb24-2"><a href="#cb24-2" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> T0<span class="op">;</span></span> | 438 | <span id="cb24-2"><a href="#cb24-2" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> T0<span class="op">;</span></span> |
| 297 | <span id="cb24-3"><a href="#cb24-3" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T2 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> T1<span class="op">;</span></span></code></pre></div> | 439 | <span id="cb24-3"><a href="#cb24-3" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T2 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> T1<span class="op">;</span></span></code></pre></div> |
| 298 | <p>In general:</p> | 440 | <p>In general:</p> |
| 299 | <div class="sourceCode" id="cb25"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb25-1"><a href="#cb25-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> <span class="op"><</span><span class="kw">return</span> <span class="kw">type</span>><span class="op">;</span></span> | 441 | <div class="sourceCode" id="cb25"><pre |
| 442 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb25-1"><a href="#cb25-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> <span class="op"><</span><span class="cf">return</span> <span class="kw">type</span>><span class="op">;</span></span> | ||
| 300 | <span id="cb25-2"><a href="#cb25-2" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="op"><</span><span class="kw">type</span> of arg N>) -> T0<span class="op">;</span></span> | 443 | <span id="cb25-2"><a href="#cb25-2" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="op"><</span><span class="kw">type</span> of arg N>) -> T0<span class="op">;</span></span> |
| 301 | <span id="cb25-3"><a href="#cb25-3" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T2 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="op"><</span><span class="kw">type</span> of arg N - 1>) -> T1<span class="op">;</span></span> | 444 | <span id="cb25-3"><a href="#cb25-3" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T2 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="op"><</span><span class="kw">type</span> of arg N - 1>) -> T1<span class="op">;</span></span> |
| 302 | <span id="cb25-4"><a href="#cb25-4" aria-hidden="true" tabindex="-1"></a><span class="op">.</span></span> | 445 | <span id="cb25-4"><a href="#cb25-4" aria-hidden="true" tabindex="-1"></a><span class="op">.</span></span> |
| @@ -308,42 +451,59 @@ syn::token::Fn --' / \ (output) | |||
| 308 | <li>all our inputs (arguments)</li> | 451 | <li>all our inputs (arguments)</li> |
| 309 | <li>the output (the return type)</li> | 452 | <li>the output (the return type)</li> |
| 310 | </ul> | 453 | </ul> |
| 311 | <p>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: <a href="https://docs.rs/syn/1.0.18/syn/enum.Type.html">Type</a>)</p> | 454 | <p>To fetch the types of all our inputs, we can simply reuse the bits we |
| 312 | <div class="sourceCode" id="cb26"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb26-1"><a href="#cb26-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | 455 | wrote to fetch the names of all our inputs! (doc: <a |
| 456 | href="https://docs.rs/syn/1.0.18/syn/enum.Type.html">Type</a>)</p> | ||
| 457 | <div class="sourceCode" id="cb26"><pre | ||
| 458 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb26-1"><a href="#cb26-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | ||
| 313 | <span id="cb26-2"><a href="#cb26-2" aria-hidden="true" tabindex="-1"></a></span> | 459 | <span id="cb26-2"><a href="#cb26-2" aria-hidden="true" tabindex="-1"></a></span> |
| 314 | <span id="cb26-3"><a href="#cb26-3" aria-hidden="true" tabindex="-1"></a><span class="kw">use</span> <span class="pp">syn::</span><span class="op">{</span>parse_macro_input<span class="op">,</span> Block<span class="op">,</span> FnArg<span class="op">,</span> ItemFn<span class="op">,</span> Pat<span class="op">,</span> ReturnType<span class="op">,</span> Type<span class="op">};</span></span> | 460 | <span id="cb26-3"><a href="#cb26-3" aria-hidden="true" tabindex="-1"></a><span class="kw">use</span> <span class="pp">syn::</span><span class="op">{</span>parse_macro_input<span class="op">,</span> Block<span class="op">,</span> FnArg<span class="op">,</span> ItemFn<span class="op">,</span> Pat<span class="op">,</span> ReturnType<span class="op">,</span> Type<span class="op">};</span></span> |
| 315 | <span id="cb26-4"><a href="#cb26-4" aria-hidden="true" tabindex="-1"></a></span> | 461 | <span id="cb26-4"><a href="#cb26-4" aria-hidden="true" tabindex="-1"></a></span> |
| 316 | <span id="cb26-5"><a href="#cb26-5" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> extract_type(a<span class="op">:</span> FnArg) <span class="op">-></span> <span class="dt">Box</span><span class="op"><</span>Type<span class="op">></span> <span class="op">{</span></span> | 462 | <span id="cb26-5"><a href="#cb26-5" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> extract_type(a<span class="op">:</span> FnArg) <span class="op">-></span> <span class="dt">Box</span><span class="op"><</span>Type<span class="op">></span> <span class="op">{</span></span> |
| 317 | <span id="cb26-6"><a href="#cb26-6" aria-hidden="true" tabindex="-1"></a> <span class="kw">match</span> a <span class="op">{</span></span> | 463 | <span id="cb26-6"><a href="#cb26-6" aria-hidden="true" tabindex="-1"></a> <span class="cf">match</span> a <span class="op">{</span></span> |
| 318 | <span id="cb26-7"><a href="#cb26-7" aria-hidden="true" tabindex="-1"></a> <span class="pp">FnArg::</span>Typed(p) <span class="op">=></span> p<span class="op">.</span>ty<span class="op">,</span> <span class="co">// notice `ty` instead of `pat`</span></span> | 464 | <span id="cb26-7"><a href="#cb26-7" aria-hidden="true" tabindex="-1"></a> <span class="pp">FnArg::</span>Typed(p) <span class="op">=></span> p<span class="op">.</span>ty<span class="op">,</span> <span class="co">// notice `ty` instead of `pat`</span></span> |
| 319 | <span id="cb26-8"><a href="#cb26-8" aria-hidden="true" tabindex="-1"></a> _ <span class="op">=></span> <span class="pp">panic!</span>(<span class="st">"Not supported on types with `self`!"</span>)<span class="op">,</span></span> | 465 | <span id="cb26-8"><a href="#cb26-8" aria-hidden="true" tabindex="-1"></a> _ <span class="op">=></span> <span class="pp">panic!</span>(<span class="st">"Not supported on types with `self`!"</span>)<span class="op">,</span></span> |
| 320 | <span id="cb26-9"><a href="#cb26-9" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> | 466 | <span id="cb26-9"><a href="#cb26-9" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> |
| 321 | <span id="cb26-10"><a href="#cb26-10" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span> | 467 | <span id="cb26-10"><a href="#cb26-10" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span> |
| 322 | <span id="cb26-11"><a href="#cb26-11" aria-hidden="true" tabindex="-1"></a></span> | 468 | <span id="cb26-11"><a href="#cb26-11" aria-hidden="true" tabindex="-1"></a></span> |
| 323 | <span id="cb26-12"><a href="#cb26-12" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> extract_arg_types(fn_args<span class="op">:</span> Punctuated<span class="op"><</span>FnArg<span class="op">,</span> <span class="pp">syn::token::</span>Comma<span class="op">></span>) <span class="op">-></span> <span class="dt">Vec</span><span class="op"><</span><span class="dt">Box</span><span class="op"><</span>Type<span class="op">>></span> <span class="op">{</span></span> | 469 | <span id="cb26-12"><a href="#cb26-12" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> extract_arg_types(fn_args<span class="op">:</span> Punctuated<span class="op"><</span>FnArg<span class="op">,</span> <span class="pp">syn::token::</span>Comma<span class="op">></span>) <span class="op">-></span> <span class="dt">Vec</span><span class="op"><</span><span class="dt">Box</span><span class="op"><</span>Type<span class="op">>></span> <span class="op">{</span></span> |
| 324 | <span id="cb26-13"><a href="#cb26-13" aria-hidden="true" tabindex="-1"></a> <span class="kw">return</span> fn_args<span class="op">.</span>into_iter()<span class="op">.</span>map(extract_type)<span class="op">.</span><span class="pp">collect::</span><span class="op"><</span><span class="dt">Vec</span><span class="op"><</span>_<span class="op">>></span>()<span class="op">;</span></span> | 470 | <span id="cb26-13"><a href="#cb26-13" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> fn_args<span class="op">.</span>into_iter()<span class="op">.</span>map(extract_type)<span class="op">.</span><span class="pp">collect::</span><span class="op"><</span><span class="dt">Vec</span><span class="op"><</span>_<span class="op">>></span>()<span class="op">;</span></span> |
| 325 | <span id="cb26-14"><a href="#cb26-14" aria-hidden="true" tabindex="-1"></a></span> | 471 | <span id="cb26-14"><a href="#cb26-14" aria-hidden="true" tabindex="-1"></a></span> |
| 326 | <span id="cb26-15"><a href="#cb26-15" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> | 472 | <span id="cb26-15"><a href="#cb26-15" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> |
| 327 | <p>A good reader would have looked at the docs for output member of the <code>syn::Signature</code> struct. It has the type <code>syn::ReturnType</code>. So there is no extraction to do here right? There are actually a couple of things we have to ensure here:</p> | 473 | <p>A good reader would have looked at the docs for output member of the |
| 474 | <code>syn::Signature</code> struct. It has the type | ||
| 475 | <code>syn::ReturnType</code>. So there is no extraction to do here | ||
| 476 | right? There are actually a couple of things we have to ensure here:</p> | ||
| 328 | <ol type="1"> | 477 | <ol type="1"> |
| 329 | <li><p>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 <a href="#notes">Notes</a> section.</p></li> | 478 | <li><p>We need to ensure that the function returns! A function that does |
| 330 | <li><p>A <code>ReturnType</code> encloses the arrow of the return as well, we need to get rid of that. Recall:</p> | 479 | not return is pointless in this case, and I will tell you why, in the <a |
| 331 | <div class="sourceCode" id="cb27"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb27-1"><a href="#cb27-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> <span class="dt">u32</span></span> | 480 | href="#notes">Notes</a> section.</p></li> |
| 481 | <li><p>A <code>ReturnType</code> encloses the arrow of the return as | ||
| 482 | well, we need to get rid of that. Recall:</p> | ||
| 483 | <div class="sourceCode" id="cb27"><pre | ||
| 484 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb27-1"><a href="#cb27-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> <span class="dt">u32</span></span> | ||
| 332 | <span id="cb27-2"><a href="#cb27-2" aria-hidden="true" tabindex="-1"></a><span class="co">// and not</span></span> | 485 | <span id="cb27-2"><a href="#cb27-2" aria-hidden="true" tabindex="-1"></a><span class="co">// and not</span></span> |
| 333 | <span id="cb27-3"><a href="#cb27-3" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> <span class="op">-></span> <span class="dt">u32</span></span></code></pre></div></li> | 486 | <span id="cb27-3"><a href="#cb27-3" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> <span class="op">-></span> <span class="dt">u32</span></span></code></pre></div></li> |
| 334 | </ol> | 487 | </ol> |
| 335 | <p>Here is the snippet that handles extraction of the return type (doc: <a href="https://docs.rs/syn/1.0.19/syn/enum.ReturnType.html">syn::ReturnType</a>):</p> | 488 | <p>Here is the snippet that handles extraction of the return type (doc: |
| 336 | <div class="sourceCode" id="cb28"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb28-1"><a href="#cb28-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | 489 | <a |
| 490 | href="https://docs.rs/syn/1.0.19/syn/enum.ReturnType.html">syn::ReturnType</a>):</p> | ||
| 491 | <div class="sourceCode" id="cb28"><pre | ||
| 492 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb28-1"><a href="#cb28-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | ||
| 337 | <span id="cb28-2"><a href="#cb28-2" aria-hidden="true" tabindex="-1"></a></span> | 493 | <span id="cb28-2"><a href="#cb28-2" aria-hidden="true" tabindex="-1"></a></span> |
| 338 | <span id="cb28-3"><a href="#cb28-3" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> extract_return_type(a<span class="op">:</span> ReturnType) <span class="op">-></span> <span class="dt">Box</span><span class="op"><</span>Type<span class="op">></span> <span class="op">{</span></span> | 494 | <span id="cb28-3"><a href="#cb28-3" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> extract_return_type(a<span class="op">:</span> ReturnType) <span class="op">-></span> <span class="dt">Box</span><span class="op"><</span>Type<span class="op">></span> <span class="op">{</span></span> |
| 339 | <span id="cb28-4"><a href="#cb28-4" aria-hidden="true" tabindex="-1"></a> <span class="kw">match</span> a <span class="op">{</span></span> | 495 | <span id="cb28-4"><a href="#cb28-4" aria-hidden="true" tabindex="-1"></a> <span class="cf">match</span> a <span class="op">{</span></span> |
| 340 | <span id="cb28-5"><a href="#cb28-5" aria-hidden="true" tabindex="-1"></a> <span class="pp">ReturnType::</span>Type(_<span class="op">,</span> p) <span class="op">=></span> p<span class="op">,</span></span> | 496 | <span id="cb28-5"><a href="#cb28-5" aria-hidden="true" tabindex="-1"></a> <span class="pp">ReturnType::</span>Type(_<span class="op">,</span> p) <span class="op">=></span> p<span class="op">,</span></span> |
| 341 | <span id="cb28-6"><a href="#cb28-6" aria-hidden="true" tabindex="-1"></a> _ <span class="op">=></span> <span class="pp">panic!</span>(<span class="st">"Not supported on functions without return types!"</span>)<span class="op">,</span></span> | 497 | <span id="cb28-6"><a href="#cb28-6" aria-hidden="true" tabindex="-1"></a> _ <span class="op">=></span> <span class="pp">panic!</span>(<span class="st">"Not supported on functions without return types!"</span>)<span class="op">,</span></span> |
| 342 | <span id="cb28-7"><a href="#cb28-7" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> | 498 | <span id="cb28-7"><a href="#cb28-7" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> |
| 343 | <span id="cb28-8"><a href="#cb28-8" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> | 499 | <span id="cb28-8"><a href="#cb28-8" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> |
| 344 | <p>You might notice that we are making extensive use of the <code>panic!</code> macro. Well, that is because it is a good idea to quit on receiving an unsatisfactory <code>TokenStream</code>.</p> | 500 | <p>You might notice that we are making extensive use of the |
| 345 | <p>With all our types ready, we can get on with generating type aliases:</p> | 501 | <code>panic!</code> macro. Well, that is because it is a good idea to |
| 346 | <div class="sourceCode" id="cb29"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb29-1"><a href="#cb29-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | 502 | quit on receiving an unsatisfactory <code>TokenStream</code>.</p> |
| 503 | <p>With all our types ready, we can get on with generating type | ||
| 504 | aliases:</p> | ||
| 505 | <div class="sourceCode" id="cb29"><pre | ||
| 506 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb29-1"><a href="#cb29-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | ||
| 347 | <span id="cb29-2"><a href="#cb29-2" aria-hidden="true" tabindex="-1"></a></span> | 507 | <span id="cb29-2"><a href="#cb29-2" aria-hidden="true" tabindex="-1"></a></span> |
| 348 | <span id="cb29-3"><a href="#cb29-3" aria-hidden="true" tabindex="-1"></a><span class="kw">use</span> <span class="pp">quote::</span><span class="op">{</span>quote<span class="op">,</span> format_ident<span class="op">};</span></span> | 508 | <span id="cb29-3"><a href="#cb29-3" aria-hidden="true" tabindex="-1"></a><span class="kw">use</span> <span class="pp">quote::</span><span class="op">{</span>quote<span class="op">,</span> format_ident<span class="op">};</span></span> |
| 349 | <span id="cb29-4"><a href="#cb29-4" aria-hidden="true" tabindex="-1"></a></span> | 509 | <span id="cb29-4"><a href="#cb29-4" aria-hidden="true" tabindex="-1"></a></span> |
| @@ -357,7 +517,7 @@ syn::token::Fn --' / \ (output) | |||
| 357 | <span id="cb29-12"><a href="#cb29-12" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> <span class="kw">mut</span> type_aliases <span class="op">=</span> <span class="pp">vec!</span>[<span class="pp">quote!</span> <span class="op">{</span> <span class="kw">type</span> #type_t0 <span class="op">=</span> #fn_return_type <span class="op">}</span>]<span class="op">;</span></span> | 517 | <span id="cb29-12"><a href="#cb29-12" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> <span class="kw">mut</span> type_aliases <span class="op">=</span> <span class="pp">vec!</span>[<span class="pp">quote!</span> <span class="op">{</span> <span class="kw">type</span> #type_t0 <span class="op">=</span> #fn_return_type <span class="op">}</span>]<span class="op">;</span></span> |
| 358 | <span id="cb29-13"><a href="#cb29-13" aria-hidden="true" tabindex="-1"></a></span> | 518 | <span id="cb29-13"><a href="#cb29-13" aria-hidden="true" tabindex="-1"></a></span> |
| 359 | <span id="cb29-14"><a href="#cb29-14" aria-hidden="true" tabindex="-1"></a> <span class="co">// 3</span></span> | 519 | <span id="cb29-14"><a href="#cb29-14" aria-hidden="true" tabindex="-1"></a> <span class="co">// 3</span></span> |
| 360 | <span id="cb29-15"><a href="#cb29-15" aria-hidden="true" tabindex="-1"></a> <span class="kw">for</span> (i<span class="op">,</span> t) <span class="kw">in</span> (<span class="dv">1</span><span class="op">..</span>)<span class="op">.</span>zip(fn_arg_types<span class="op">.</span>into_iter()<span class="op">.</span>rev()) <span class="op">{</span></span> | 520 | <span id="cb29-15"><a href="#cb29-15" aria-hidden="true" tabindex="-1"></a> <span class="cf">for</span> (i<span class="op">,</span> t) <span class="kw">in</span> (<span class="dv">1</span><span class="op">..</span>)<span class="op">.</span>zip(fn_arg_types<span class="op">.</span>into_iter()<span class="op">.</span>rev()) <span class="op">{</span></span> |
| 361 | <span id="cb29-16"><a href="#cb29-16" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> p <span class="op">=</span> <span class="pp">format_ident!</span>(<span class="st">"_{}_{}"</span><span class="op">,</span> fn_name<span class="op">,</span> <span class="pp">format!</span>(<span class="st">"T{}"</span><span class="op">,</span> i <span class="op">-</span> <span class="dv">1</span>))<span class="op">;</span></span> | 521 | <span id="cb29-16"><a href="#cb29-16" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> p <span class="op">=</span> <span class="pp">format_ident!</span>(<span class="st">"_{}_{}"</span><span class="op">,</span> fn_name<span class="op">,</span> <span class="pp">format!</span>(<span class="st">"T{}"</span><span class="op">,</span> i <span class="op">-</span> <span class="dv">1</span>))<span class="op">;</span></span> |
| 362 | <span id="cb29-17"><a href="#cb29-17" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> n <span class="op">=</span> <span class="pp">format_ident!</span>(<span class="st">"_{}_{}"</span><span class="op">,</span> fn_name<span class="op">,</span> <span class="pp">format!</span>(<span class="st">"T{}"</span><span class="op">,</span> i))<span class="op">;</span></span> | 522 | <span id="cb29-17"><a href="#cb29-17" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> n <span class="op">=</span> <span class="pp">format_ident!</span>(<span class="st">"_{}_{}"</span><span class="op">,</span> fn_name<span class="op">,</span> <span class="pp">format!</span>(<span class="st">"T{}"</span><span class="op">,</span> i))<span class="op">;</span></span> |
| 363 | <span id="cb29-18"><a href="#cb29-18" aria-hidden="true" tabindex="-1"></a></span> | 523 | <span id="cb29-18"><a href="#cb29-18" aria-hidden="true" tabindex="-1"></a></span> |
| @@ -366,45 +526,70 @@ syn::token::Fn --' / \ (output) | |||
| 366 | <span id="cb29-21"><a href="#cb29-21" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span>)<span class="op">;</span></span> | 526 | <span id="cb29-21"><a href="#cb29-21" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span>)<span class="op">;</span></span> |
| 367 | <span id="cb29-22"><a href="#cb29-22" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> | 527 | <span id="cb29-22"><a href="#cb29-22" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> |
| 368 | <span id="cb29-23"><a href="#cb29-23" aria-hidden="true" tabindex="-1"></a></span> | 528 | <span id="cb29-23"><a href="#cb29-23" aria-hidden="true" tabindex="-1"></a></span> |
| 369 | <span id="cb29-24"><a href="#cb29-24" aria-hidden="true" tabindex="-1"></a> <span class="kw">return</span> type_aliases<span class="op">;</span></span> | 529 | <span id="cb29-24"><a href="#cb29-24" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> type_aliases<span class="op">;</span></span> |
| 370 | <span id="cb29-25"><a href="#cb29-25" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> | 530 | <span id="cb29-25"><a href="#cb29-25" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> |
| 371 | <p><strong>1. The return value</strong><br /> | 531 | <p><strong>1. The return value</strong><br /> |
| 372 | We are returning a <code>Vec<proc_macro2::TokenStream></code>, i. e., a list of <code>TokenStream</code>s, where each item is a type alias.</p> | 532 | We are returning a <code>Vec<proc_macro2::TokenStream></code>, i. |
| 533 | e., a list of <code>TokenStream</code>s, where each item is a type | ||
| 534 | alias.</p> | ||
| 373 | <p><strong>2. Format identifier?</strong><br /> | 535 | <p><strong>2. Format identifier?</strong><br /> |
| 374 | I’ve got some explanation to do on this line. Clearly, we are trying to write the first type alias, and initialize our <code>TokenStream</code> vector with <code>T0</code>, because it is different from the others:</p> | 536 | I’ve got some explanation to do on this line. Clearly, we are trying to |
| 375 | <div class="sourceCode" id="cb30"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb30-1"><a href="#cb30-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> something</span> | 537 | write the first type alias, and initialize our <code>TokenStream</code> |
| 538 | vector with <code>T0</code>, because it is different from the | ||
| 539 | others:</p> | ||
| 540 | <div class="sourceCode" id="cb30"><pre | ||
| 541 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb30-1"><a href="#cb30-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> something</span> | ||
| 376 | <span id="cb30-2"><a href="#cb30-2" aria-hidden="true" tabindex="-1"></a><span class="co">// the others are of the form</span></span> | 542 | <span id="cb30-2"><a href="#cb30-2" aria-hidden="true" tabindex="-1"></a><span class="co">// the others are of the form</span></span> |
| 377 | <span id="cb30-3"><a href="#cb30-3" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> Tr <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(something) <span class="op">-></span> something</span></code></pre></div> | 543 | <span id="cb30-3"><a href="#cb30-3" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> Tr <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(something) <span class="op">-></span> something</span></code></pre></div> |
| 378 | <p><code>format_ident!</code> is similar to <code>format!</code>. Instead of returning a formatted string, it returns a <code>syn::Ident</code>. Therefore, <code>type_t0</code> is actually an identifier for, in the case of our <code>add</code> function, <code>_add_T0</code>. Why is this formatting important? Namespacing.</p> | 544 | <p><code>format_ident!</code> is similar to <code>format!</code>. |
| 379 | <p>Picture this, we have two functions, <code>add</code> and <code>subtract</code>, that we wish to curry with our macro:</p> | 545 | Instead of returning a formatted string, it returns a |
| 380 | <div class="sourceCode" id="cb31"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb31-1"><a href="#cb31-1" aria-hidden="true" tabindex="-1"></a><span class="at">#[</span>curry<span class="at">]</span></span> | 546 | <code>syn::Ident</code>. Therefore, <code>type_t0</code> is actually an |
| 547 | identifier for, in the case of our <code>add</code> function, | ||
| 548 | <code>_add_T0</code>. Why is this formatting important? Namespacing.</p> | ||
| 549 | <p>Picture this, we have two functions, <code>add</code> and | ||
| 550 | <code>subtract</code>, that we wish to curry with our macro:</p> | ||
| 551 | <div class="sourceCode" id="cb31"><pre | ||
| 552 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb31-1"><a href="#cb31-1" aria-hidden="true" tabindex="-1"></a><span class="at">#[</span>curry<span class="at">]</span></span> | ||
| 381 | <span id="cb31-2"><a href="#cb31-2" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add(<span class="op">...</span>) <span class="op">-></span> <span class="dt">u32</span> <span class="op">{</span> <span class="op">...</span> <span class="op">}</span></span> | 553 | <span id="cb31-2"><a href="#cb31-2" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add(<span class="op">...</span>) <span class="op">-></span> <span class="dt">u32</span> <span class="op">{</span> <span class="op">...</span> <span class="op">}</span></span> |
| 382 | <span id="cb31-3"><a href="#cb31-3" aria-hidden="true" tabindex="-1"></a></span> | 554 | <span id="cb31-3"><a href="#cb31-3" aria-hidden="true" tabindex="-1"></a></span> |
| 383 | <span id="cb31-4"><a href="#cb31-4" aria-hidden="true" tabindex="-1"></a><span class="at">#[</span>curry<span class="at">]</span></span> | 555 | <span id="cb31-4"><a href="#cb31-4" aria-hidden="true" tabindex="-1"></a><span class="at">#[</span>curry<span class="at">]</span></span> |
| 384 | <span id="cb31-5"><a href="#cb31-5" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> sub(<span class="op">...</span>) <span class="op">-></span> <span class="dt">u32</span> <span class="op">{</span> <span class="op">...</span> <span class="op">}</span></span></code></pre></div> | 556 | <span id="cb31-5"><a href="#cb31-5" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> sub(<span class="op">...</span>) <span class="op">-></span> <span class="dt">u32</span> <span class="op">{</span> <span class="op">...</span> <span class="op">}</span></span></code></pre></div> |
| 385 | <p>Here is the same but with macros expanded:</p> | 557 | <p>Here is the same but with macros expanded:</p> |
| 386 | <div class="sourceCode" id="cb32"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb32-1"><a href="#cb32-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> <span class="dt">u32</span><span class="op">;</span></span> | 558 | <div class="sourceCode" id="cb32"><pre |
| 559 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb32-1"><a href="#cb32-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> <span class="dt">u32</span><span class="op">;</span></span> | ||
| 387 | <span id="cb32-2"><a href="#cb32-2" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> T0<span class="op">;</span></span> | 560 | <span id="cb32-2"><a href="#cb32-2" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> T0<span class="op">;</span></span> |
| 388 | <span id="cb32-3"><a href="#cb32-3" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add( <span class="op">...</span> ) <span class="op">-></span> T1 <span class="op">{</span> <span class="op">...</span> <span class="op">}</span></span> | 561 | <span id="cb32-3"><a href="#cb32-3" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add( <span class="op">...</span> ) <span class="op">-></span> T1 <span class="op">{</span> <span class="op">...</span> <span class="op">}</span></span> |
| 389 | <span id="cb32-4"><a href="#cb32-4" aria-hidden="true" tabindex="-1"></a></span> | 562 | <span id="cb32-4"><a href="#cb32-4" aria-hidden="true" tabindex="-1"></a></span> |
| 390 | <span id="cb32-5"><a href="#cb32-5" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> <span class="dt">u32</span><span class="op">;</span></span> | 563 | <span id="cb32-5"><a href="#cb32-5" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T0 <span class="op">=</span> <span class="dt">u32</span><span class="op">;</span></span> |
| 391 | <span id="cb32-6"><a href="#cb32-6" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> T0<span class="op">;</span></span> | 564 | <span id="cb32-6"><a href="#cb32-6" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> T0<span class="op">;</span></span> |
| 392 | <span id="cb32-7"><a href="#cb32-7" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> sub( <span class="op">...</span> ) <span class="op">-></span> T1 <span class="op">{</span> <span class="op">...</span> <span class="op">}</span></span></code></pre></div> | 565 | <span id="cb32-7"><a href="#cb32-7" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> sub( <span class="op">...</span> ) <span class="op">-></span> T1 <span class="op">{</span> <span class="op">...</span> <span class="op">}</span></span></code></pre></div> |
| 393 | <p>We end up with two definitions of <code>T0</code>! Now, if we do the little <code>format_ident!</code> dance we did up there:</p> | 566 | <p>We end up with two definitions of <code>T0</code>! Now, if we do the |
| 394 | <div class="sourceCode" id="cb33"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb33-1"><a href="#cb33-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> _add_T0 <span class="op">=</span> <span class="dt">u32</span><span class="op">;</span></span> | 567 | little <code>format_ident!</code> dance we did up there:</p> |
| 568 | <div class="sourceCode" id="cb33"><pre | ||
| 569 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb33-1"><a href="#cb33-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> _add_T0 <span class="op">=</span> <span class="dt">u32</span><span class="op">;</span></span> | ||
| 395 | <span id="cb33-2"><a href="#cb33-2" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> _add_T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> _add_T0<span class="op">;</span></span> | 570 | <span id="cb33-2"><a href="#cb33-2" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> _add_T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> _add_T0<span class="op">;</span></span> |
| 396 | <span id="cb33-3"><a href="#cb33-3" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add( <span class="op">...</span> ) <span class="op">-></span> _add_T1 <span class="op">{</span> <span class="op">...</span> <span class="op">}</span></span> | 571 | <span id="cb33-3"><a href="#cb33-3" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add( <span class="op">...</span> ) <span class="op">-></span> _add_T1 <span class="op">{</span> <span class="op">...</span> <span class="op">}</span></span> |
| 397 | <span id="cb33-4"><a href="#cb33-4" aria-hidden="true" tabindex="-1"></a></span> | 572 | <span id="cb33-4"><a href="#cb33-4" aria-hidden="true" tabindex="-1"></a></span> |
| 398 | <span id="cb33-5"><a href="#cb33-5" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> _sub_T0 <span class="op">=</span> <span class="dt">u32</span><span class="op">;</span></span> | 573 | <span id="cb33-5"><a href="#cb33-5" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> _sub_T0 <span class="op">=</span> <span class="dt">u32</span><span class="op">;</span></span> |
| 399 | <span id="cb33-6"><a href="#cb33-6" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> _sub_T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> _sub_T0<span class="op">;</span></span> | 574 | <span id="cb33-6"><a href="#cb33-6" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> _sub_T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> _sub_T0<span class="op">;</span></span> |
| 400 | <span id="cb33-7"><a href="#cb33-7" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> sub( <span class="op">...</span> ) <span class="op">-></span> _sub_T1 <span class="op">{</span> <span class="op">...</span> <span class="op">}</span></span></code></pre></div> | 575 | <span id="cb33-7"><a href="#cb33-7" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> sub( <span class="op">...</span> ) <span class="op">-></span> _sub_T1 <span class="op">{</span> <span class="op">...</span> <span class="op">}</span></span></code></pre></div> |
| 401 | <p>Voilà! The type aliases don’t tread on each other. Remember to import <code>format_ident</code> from the <code>quote</code> crate.</p> | 576 | <p>Voilà! The type aliases don’t tread on each other. Remember to import |
| 577 | <code>format_ident</code> from the <code>quote</code> crate.</p> | ||
| 402 | <p><strong>3. The TokenStream Vector</strong></p> | 578 | <p><strong>3. The TokenStream Vector</strong></p> |
| 403 | <p>We iterate over our types in reverse order (<code>T0</code> is the last return, <code>T1</code> is the second last, so on), assign a number to each iteration with <code>zip</code>, generate type names with <code>format_ident</code>, push a <code>TokenStream</code> with the help of <code>quote</code> and variable interpolation.</p> | 579 | <p>We iterate over our types in reverse order (<code>T0</code> is the |
| 404 | <p>If you are wondering why we used <code>(1..).zip()</code> instead of <code>.enumerate()</code>, it’s because we wanted to start counting from 1 instead of 0 (we are already done with <code>T0</code>!).</p> | 580 | last return, <code>T1</code> is the second last, so on), assign a number |
| 581 | to each iteration with <code>zip</code>, generate type names with | ||
| 582 | <code>format_ident</code>, push a <code>TokenStream</code> with the help | ||
| 583 | of <code>quote</code> and variable interpolation.</p> | ||
| 584 | <p>If you are wondering why we used <code>(1..).zip()</code> instead of | ||
| 585 | <code>.enumerate()</code>, it’s because we wanted to start counting from | ||
| 586 | 1 instead of 0 (we are already done with <code>T0</code>!).</p> | ||
| 405 | <h4 id="getting-it-together">Getting it together</h4> | 587 | <h4 id="getting-it-together">Getting it together</h4> |
| 406 | <p>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 <code>generate_curry</code> function:</p> | 588 | <p>I promised we’d have a fully working macro by the end of last |
| 407 | <div class="sourceCode" id="cb34"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb34-1"><a href="#cb34-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | 589 | section. I lied, we have to tie everything together in our |
| 590 | <code>generate_curry</code> function:</p> | ||
| 591 | <div class="sourceCode" id="cb34"><pre | ||
| 592 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb34-1"><a href="#cb34-1" aria-hidden="true" tabindex="-1"></a><span class="co">// src/lib.rs</span></span> | ||
| 408 | <span id="cb34-2"><a href="#cb34-2" aria-hidden="true" tabindex="-1"></a></span> | 593 | <span id="cb34-2"><a href="#cb34-2" aria-hidden="true" tabindex="-1"></a></span> |
| 409 | <span id="cb34-3"><a href="#cb34-3" aria-hidden="true" tabindex="-1"></a> <span class="kw">fn</span> generate_curry(parsed<span class="op">:</span> ItemFn) <span class="op">-></span> <span class="pp">proc_macro2::</span>TokenStream <span class="op">{</span></span> | 594 | <span id="cb34-3"><a href="#cb34-3" aria-hidden="true" tabindex="-1"></a> <span class="kw">fn</span> generate_curry(parsed<span class="op">:</span> ItemFn) <span class="op">-></span> <span class="pp">proc_macro2::</span>TokenStream <span class="op">{</span></span> |
| 410 | <span id="cb34-4"><a href="#cb34-4" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> fn_body <span class="op">=</span> parsed<span class="op">.</span>block<span class="op">;</span></span> | 595 | <span id="cb34-4"><a href="#cb34-4" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> fn_body <span class="op">=</span> parsed<span class="op">.</span>block<span class="op">;</span></span> |
| @@ -428,20 +613,39 @@ I’ve got some explanation to do on this line. Clearly, we are trying to write | |||
| 428 | <span id="cb34-22"><a href="#cb34-22" aria-hidden="true" tabindex="-1"></a></span> | 613 | <span id="cb34-22"><a href="#cb34-22" aria-hidden="true" tabindex="-1"></a></span> |
| 429 | <span id="cb34-23"><a href="#cb34-23" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> <span class="kw">let</span> return_type <span class="op">=</span> <span class="pp">format_ident!</span>(<span class="st">"_{}_{}"</span><span class="op">,</span> <span class="op">&</span>fn_name<span class="op">,</span> <span class="pp">format!</span>(<span class="st">"T{}"</span><span class="op">,</span> type_aliases<span class="op">.</span>len() <span class="op">-</span> <span class="dv">1</span>))<span class="op">;</span></span> | 614 | <span id="cb34-23"><a href="#cb34-23" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> <span class="kw">let</span> return_type <span class="op">=</span> <span class="pp">format_ident!</span>(<span class="st">"_{}_{}"</span><span class="op">,</span> <span class="op">&</span>fn_name<span class="op">,</span> <span class="pp">format!</span>(<span class="st">"T{}"</span><span class="op">,</span> type_aliases<span class="op">.</span>len() <span class="op">-</span> <span class="dv">1</span>))<span class="op">;</span></span> |
| 430 | <span id="cb34-24"><a href="#cb34-24" aria-hidden="true" tabindex="-1"></a></span> | 615 | <span id="cb34-24"><a href="#cb34-24" aria-hidden="true" tabindex="-1"></a></span> |
| 431 | <span id="cb34-25"><a href="#cb34-25" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> <span class="kw">return</span> <span class="pp">quote!</span> <span class="op">{</span></span> | 616 | <span id="cb34-25"><a href="#cb34-25" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> <span class="cf">return</span> <span class="pp">quote!</span> <span class="op">{</span></span> |
| 432 | <span id="cb34-26"><a href="#cb34-26" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> #(#type_aliases)<span class="op">;*</span> <span class="op">;</span></span> | 617 | <span id="cb34-26"><a href="#cb34-26" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> #(#type_aliases)<span class="op">;*</span> <span class="op">;</span></span> |
| 433 | <span id="cb34-27"><a href="#cb34-27" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> #vis <span class="kw">fn</span> #fn_name (#first_ident<span class="op">:</span> #first_type) <span class="op">-></span> #return_type <span class="op">{</span></span> | 618 | <span id="cb34-27"><a href="#cb34-27" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> #vis <span class="kw">fn</span> #fn_name (#first_ident<span class="op">:</span> #first_type) <span class="op">-></span> #return_type <span class="op">{</span></span> |
| 434 | <span id="cb34-28"><a href="#cb34-28" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> #curried_body <span class="op">;</span></span> | 619 | <span id="cb34-28"><a href="#cb34-28" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> #curried_body <span class="op">;</span></span> |
| 435 | <span id="cb34-29"><a href="#cb34-29" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> <span class="op">}</span></span> | 620 | <span id="cb34-29"><a href="#cb34-29" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> <span class="op">}</span></span> |
| 436 | <span id="cb34-30"><a href="#cb34-30" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> <span class="op">};</span></span> | 621 | <span id="cb34-30"><a href="#cb34-30" aria-hidden="true" tabindex="-1"></a><span class="op">+</span> <span class="op">};</span></span> |
| 437 | <span id="cb34-31"><a href="#cb34-31" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span></code></pre></div> | 622 | <span id="cb34-31"><a href="#cb34-31" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span></code></pre></div> |
| 438 | <p>Most of the additions are self explanatory, I’ll go through the return statement with you. We are returning a <code>quote!{ ... }</code>, so a <code>proc_macro2::TokenStream</code>. We are iterating through the <code>type_aliases</code> variable, which you might recall, is a <code>Vec<TokenStream></code>. You might notice the sneaky semicolon before the <code>*</code>. This basically tells <code>quote</code>, 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, <code>quote</code> doesn’t insert a separator at the end of the iteration.</p> | 623 | <p>Most of the additions are self explanatory, I’ll go through the |
| 439 | <p>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 <code>add</code> function, we returned <code>T2</code>, which was in fact, the last type alias we created.</p> | 624 | return statement with you. We are returning a |
| 440 | <p>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.</p> | 625 | <code>quote!{ ... }</code>, so a <code>proc_macro2::TokenStream</code>. |
| 626 | We are iterating through the <code>type_aliases</code> variable, which | ||
| 627 | you might recall, is a <code>Vec<TokenStream></code>. You might | ||
| 628 | notice the sneaky semicolon before the <code>*</code>. This basically | ||
| 629 | tells <code>quote</code>, to insert an item, then a semicolon, and then | ||
| 630 | the next one, another semicolon, and so on. The semicolon is a | ||
| 631 | separator. We need to manually insert another semicolon at the end of it | ||
| 632 | all, <code>quote</code> doesn’t insert a separator at the end of the | ||
| 633 | iteration.</p> | ||
| 634 | <p>We retain the visibility and name of our original function. Our | ||
| 635 | curried function takes as args, just the first argument of our original | ||
| 636 | function. The return type of our curried function is actually, the last | ||
| 637 | type alias we create. If you think back to our manually curried | ||
| 638 | <code>add</code> function, we returned <code>T2</code>, which was in | ||
| 639 | fact, the last type alias we created.</p> | ||
| 640 | <p>I am sure, at this point, you are itching to test this out, but | ||
| 641 | before that, let me introduce you to some good methods of debugging | ||
| 642 | proc-macro code.</p> | ||
| 441 | <h3 id="debugging-and-testing">Debugging and Testing</h3> | 643 | <h3 id="debugging-and-testing">Debugging and Testing</h3> |
| 442 | <p>Install <code>cargo-expand</code> via:</p> | 644 | <p>Install <code>cargo-expand</code> via:</p> |
| 443 | <pre><code>cargo install cargo-expand</code></pre> | 645 | <pre><code>cargo install cargo-expand</code></pre> |
| 444 | <p><code>cargo-expand</code> is a neat little tool that expands your macro in places where it is used, and lets you view the generated code! For example:</p> | 646 | <p><code>cargo-expand</code> is a neat little tool that expands your |
| 647 | macro in places where it is used, and lets you view the generated code! | ||
| 648 | For example:</p> | ||
| 445 | <pre class="shell"><code># create a bin package hello | 649 | <pre class="shell"><code># create a bin package hello |
| 446 | $ cargo new hello | 650 | $ cargo new hello |
| 447 | 651 | ||
| @@ -463,10 +667,18 @@ fn main() { | |||
| 463 | )); | 667 | )); |
| 464 | }; | 668 | }; |
| 465 | }</code></pre> | 669 | }</code></pre> |
| 466 | <p>Writing proc-macros without <code>cargo-expand</code> is tantamount to driving a vehicle without rear view mirrors! Keep an eye on what is going on behind your back.</p> | 670 | <p>Writing proc-macros without <code>cargo-expand</code> is tantamount |
| 467 | <p>Now, your macro won’t always compile, you might just recieve the bee movie script as an error. <code>cargo-expand</code> will not work in such cases. I would suggest printing out your variables to inspect them. <code>TokenStream</code> implements <code>Display</code> as well as <code>Debug</code>. We don’t always have to be respectable programmers. Just print it.</p> | 671 | to driving a vehicle without rear view mirrors! Keep an eye on what is |
| 672 | going on behind your back.</p> | ||
| 673 | <p>Now, your macro won’t always compile, you might just recieve the bee | ||
| 674 | movie script as an error. <code>cargo-expand</code> will not work in | ||
| 675 | such cases. I would suggest printing out your variables to inspect them. | ||
| 676 | <code>TokenStream</code> implements <code>Display</code> as well as | ||
| 677 | <code>Debug</code>. We don’t always have to be respectable programmers. | ||
| 678 | Just print it.</p> | ||
| 468 | <p>Enough of that, lets get testing:</p> | 679 | <p>Enough of that, lets get testing:</p> |
| 469 | <div class="sourceCode" id="cb37"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb37-1"><a href="#cb37-1" aria-hidden="true" tabindex="-1"></a><span class="co">// tests/smoke.rs</span></span> | 680 | <div class="sourceCode" id="cb37"><pre |
| 681 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb37-1"><a href="#cb37-1" aria-hidden="true" tabindex="-1"></a><span class="co">// tests/smoke.rs</span></span> | ||
| 470 | <span id="cb37-2"><a href="#cb37-2" aria-hidden="true" tabindex="-1"></a></span> | 682 | <span id="cb37-2"><a href="#cb37-2" aria-hidden="true" tabindex="-1"></a></span> |
| 471 | <span id="cb37-3"><a href="#cb37-3" aria-hidden="true" tabindex="-1"></a><span class="at">#![</span>feature<span class="at">(</span>type_alias_impl_trait<span class="at">)]</span></span> | 683 | <span id="cb37-3"><a href="#cb37-3" aria-hidden="true" tabindex="-1"></a><span class="at">#![</span>feature<span class="at">(</span>type_alias_impl_trait<span class="at">)]</span></span> |
| 472 | <span id="cb37-4"><a href="#cb37-4" aria-hidden="true" tabindex="-1"></a></span> | 684 | <span id="cb37-4"><a href="#cb37-4" aria-hidden="true" tabindex="-1"></a></span> |
| @@ -479,55 +691,81 @@ fn main() { | |||
| 479 | <span id="cb37-11"><a href="#cb37-11" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> works() <span class="op">{</span></span> | 691 | <span id="cb37-11"><a href="#cb37-11" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> works() <span class="op">{</span></span> |
| 480 | <span id="cb37-12"><a href="#cb37-12" aria-hidden="true" tabindex="-1"></a> <span class="pp">assert_eq!</span>(<span class="dv">15</span><span class="op">,</span> add(<span class="dv">4</span>)(<span class="dv">5</span>)(<span class="dv">6</span>))<span class="op">;</span></span> | 692 | <span id="cb37-12"><a href="#cb37-12" aria-hidden="true" tabindex="-1"></a> <span class="pp">assert_eq!</span>(<span class="dv">15</span><span class="op">,</span> add(<span class="dv">4</span>)(<span class="dv">5</span>)(<span class="dv">6</span>))<span class="op">;</span></span> |
| 481 | <span id="cb37-13"><a href="#cb37-13" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> | 693 | <span id="cb37-13"><a href="#cb37-13" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> |
| 482 | <p>Run <code>cargo +nightly test</code>. You should see a pleasing message:</p> | 694 | <p>Run <code>cargo +nightly test</code>. You should see a pleasing |
| 695 | message:</p> | ||
| 483 | <pre><code>running 1 test | 696 | <pre><code>running 1 test |
| 484 | test tests::works ... ok</code></pre> | 697 | test tests::works ... ok</code></pre> |
| 485 | <p>Take a look at the expansion for our curry macro, via <code>cargo +nightly expand --tests smoke</code>:</p> | 698 | <p>Take a look at the expansion for our curry macro, via |
| 486 | <div class="sourceCode" id="cb39"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb39-1"><a href="#cb39-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> _add_T0 <span class="op">=</span> <span class="dt">u32</span><span class="op">;</span></span> | 699 | <code>cargo +nightly expand --tests smoke</code>:</p> |
| 700 | <div class="sourceCode" id="cb39"><pre | ||
| 701 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb39-1"><a href="#cb39-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> _add_T0 <span class="op">=</span> <span class="dt">u32</span><span class="op">;</span></span> | ||
| 487 | <span id="cb39-2"><a href="#cb39-2" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> _add_T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> _add_T0<span class="op">;</span></span> | 702 | <span id="cb39-2"><a href="#cb39-2" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> _add_T1 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> _add_T0<span class="op">;</span></span> |
| 488 | <span id="cb39-3"><a href="#cb39-3" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> _add_T2 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> _add_T1<span class="op">;</span></span> | 703 | <span id="cb39-3"><a href="#cb39-3" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> _add_T2 <span class="op">=</span> <span class="kw">impl</span> <span class="bu">Fn</span>(<span class="dt">u32</span>) <span class="op">-></span> _add_T1<span class="op">;</span></span> |
| 489 | <span id="cb39-4"><a href="#cb39-4" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add(x<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> _add_T2 <span class="op">{</span></span> | 704 | <span id="cb39-4"><a href="#cb39-4" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> add(x<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> _add_T2 <span class="op">{</span></span> |
| 490 | <span id="cb39-5"><a href="#cb39-5" aria-hidden="true" tabindex="-1"></a> <span class="kw">return</span> (<span class="kw">move</span> <span class="op">|</span>y<span class="op">|</span> <span class="op">{</span></span> | 705 | <span id="cb39-5"><a href="#cb39-5" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> (<span class="kw">move</span> <span class="op">|</span>y<span class="op">|</span> <span class="op">{</span></span> |
| 491 | <span id="cb39-6"><a href="#cb39-6" aria-hidden="true" tabindex="-1"></a> <span class="kw">move</span> <span class="op">|</span>z<span class="op">|</span> <span class="op">{</span></span> | 706 | <span id="cb39-6"><a href="#cb39-6" aria-hidden="true" tabindex="-1"></a> <span class="kw">move</span> <span class="op">|</span>z<span class="op">|</span> <span class="op">{</span></span> |
| 492 | <span id="cb39-7"><a href="#cb39-7" aria-hidden="true" tabindex="-1"></a> <span class="kw">return</span> x <span class="op">+</span> y <span class="op">+</span> z<span class="op">;</span></span> | 707 | <span id="cb39-7"><a href="#cb39-7" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> x <span class="op">+</span> y <span class="op">+</span> z<span class="op">;</span></span> |
| 493 | <span id="cb39-8"><a href="#cb39-8" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> | 708 | <span id="cb39-8"><a href="#cb39-8" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span> |
| 494 | <span id="cb39-9"><a href="#cb39-9" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span>)<span class="op">;</span></span> | 709 | <span id="cb39-9"><a href="#cb39-9" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span>)<span class="op">;</span></span> |
| 495 | <span id="cb39-10"><a href="#cb39-10" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span> | 710 | <span id="cb39-10"><a href="#cb39-10" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span> |
| 496 | <span id="cb39-11"><a href="#cb39-11" aria-hidden="true" tabindex="-1"></a></span> | 711 | <span id="cb39-11"><a href="#cb39-11" aria-hidden="true" tabindex="-1"></a></span> |
| 497 | <span id="cb39-12"><a href="#cb39-12" aria-hidden="true" tabindex="-1"></a><span class="co">// a bunch of other stuff generated by #[test] and assert_eq!</span></span></code></pre></div> | 712 | <span id="cb39-12"><a href="#cb39-12" aria-hidden="true" tabindex="-1"></a><span class="co">// a bunch of other stuff generated by #[test] and assert_eq!</span></span></code></pre></div> |
| 498 | <p>A sight for sore eyes.</p> | 713 | <p>A sight for sore eyes.</p> |
| 499 | <p>Here is a more complex example that generates ten multiples of the first ten natural numbers:</p> | 714 | <p>Here is a more complex example that generates ten multiples of the |
| 500 | <div class="sourceCode" id="cb40"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb40-1"><a href="#cb40-1" aria-hidden="true" tabindex="-1"></a><span class="at">#[</span>curry<span class="at">]</span></span> | 715 | first ten natural numbers:</p> |
| 716 | <div class="sourceCode" id="cb40"><pre | ||
| 717 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb40-1"><a href="#cb40-1" aria-hidden="true" tabindex="-1"></a><span class="at">#[</span>curry<span class="at">]</span></span> | ||
| 501 | <span id="cb40-2"><a href="#cb40-2" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> product(x<span class="op">:</span> <span class="dt">u32</span><span class="op">,</span> y<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> <span class="dt">u32</span> <span class="op">{</span></span> | 718 | <span id="cb40-2"><a href="#cb40-2" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> product(x<span class="op">:</span> <span class="dt">u32</span><span class="op">,</span> y<span class="op">:</span> <span class="dt">u32</span>) <span class="op">-></span> <span class="dt">u32</span> <span class="op">{</span></span> |
| 502 | <span id="cb40-3"><a href="#cb40-3" aria-hidden="true" tabindex="-1"></a> x <span class="op">*</span> y</span> | 719 | <span id="cb40-3"><a href="#cb40-3" aria-hidden="true" tabindex="-1"></a> x <span class="op">*</span> y</span> |
| 503 | <span id="cb40-4"><a href="#cb40-4" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span> | 720 | <span id="cb40-4"><a href="#cb40-4" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span> |
| 504 | <span id="cb40-5"><a href="#cb40-5" aria-hidden="true" tabindex="-1"></a></span> | 721 | <span id="cb40-5"><a href="#cb40-5" aria-hidden="true" tabindex="-1"></a></span> |
| 505 | <span id="cb40-6"><a href="#cb40-6" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> multiples() <span class="op">-></span> <span class="dt">Vec</span><span class="op"><</span><span class="dt">Vec</span><span class="op"><</span><span class="dt">u32</span><span class="op">>>{</span></span> | 722 | <span id="cb40-6"><a href="#cb40-6" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> multiples() <span class="op">-></span> <span class="dt">Vec</span><span class="op"><</span><span class="dt">Vec</span><span class="op"><</span><span class="dt">u32</span><span class="op">>>{</span></span> |
| 506 | <span id="cb40-7"><a href="#cb40-7" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> v <span class="op">=</span> (<span class="dv">1</span><span class="op">..=</span><span class="dv">10</span>)<span class="op">.</span>map(product)<span class="op">;</span></span> | 723 | <span id="cb40-7"><a href="#cb40-7" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> v <span class="op">=</span> (<span class="dv">1</span><span class="op">..=</span><span class="dv">10</span>)<span class="op">.</span>map(product)<span class="op">;</span></span> |
| 507 | <span id="cb40-8"><a href="#cb40-8" aria-hidden="true" tabindex="-1"></a> <span class="kw">return</span> (<span class="dv">1</span><span class="op">..=</span><span class="dv">10</span>)</span> | 724 | <span id="cb40-8"><a href="#cb40-8" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> (<span class="dv">1</span><span class="op">..=</span><span class="dv">10</span>)</span> |
| 508 | <span id="cb40-9"><a href="#cb40-9" aria-hidden="true" tabindex="-1"></a> <span class="op">.</span>map(<span class="op">|</span>x<span class="op">|</span> v<span class="op">.</span>clone()<span class="op">.</span>map(<span class="op">|</span>f<span class="op">|</span> f(x))<span class="op">.</span>collect())</span> | 725 | <span id="cb40-9"><a href="#cb40-9" aria-hidden="true" tabindex="-1"></a> <span class="op">.</span>map(<span class="op">|</span>x<span class="op">|</span> v<span class="op">.</span>clone()<span class="op">.</span>map(<span class="op">|</span>f<span class="op">|</span> f(x))<span class="op">.</span>collect())</span> |
| 509 | <span id="cb40-10"><a href="#cb40-10" aria-hidden="true" tabindex="-1"></a> <span class="op">.</span>collect()<span class="op">;</span></span> | 726 | <span id="cb40-10"><a href="#cb40-10" aria-hidden="true" tabindex="-1"></a> <span class="op">.</span>collect()<span class="op">;</span></span> |
| 510 | <span id="cb40-11"><a href="#cb40-11" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> | 727 | <span id="cb40-11"><a href="#cb40-11" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div> |
| 511 | <h3 id="notes">Notes</h3> | 728 | <h3 id="notes">Notes</h3> |
| 512 | <p>I didn’t quite explain why we use <code>move |arg|</code> in our closure. This is because we want to take ownership of the variable supplied to us. Take a look at this example:</p> | 729 | <p>I didn’t quite explain why we use <code>move |arg|</code> in our |
| 513 | <div class="sourceCode" id="cb41"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb41-1"><a href="#cb41-1" aria-hidden="true" tabindex="-1"></a><span class="kw">let</span> v <span class="op">=</span> add(<span class="dv">5</span>)<span class="op">;</span></span> | 730 | closure. This is because we want to take ownership of the variable |
| 731 | supplied to us. Take a look at this example:</p> | ||
| 732 | <div class="sourceCode" id="cb41"><pre | ||
| 733 | class="sourceCode rust"><code class="sourceCode rust"><span id="cb41-1"><a href="#cb41-1" aria-hidden="true" tabindex="-1"></a><span class="kw">let</span> v <span class="op">=</span> add(<span class="dv">5</span>)<span class="op">;</span></span> | ||
| 514 | <span id="cb41-2"><a href="#cb41-2" aria-hidden="true" tabindex="-1"></a><span class="kw">let</span> g<span class="op">;</span></span> | 734 | <span id="cb41-2"><a href="#cb41-2" aria-hidden="true" tabindex="-1"></a><span class="kw">let</span> g<span class="op">;</span></span> |
| 515 | <span id="cb41-3"><a href="#cb41-3" aria-hidden="true" tabindex="-1"></a><span class="op">{</span></span> | 735 | <span id="cb41-3"><a href="#cb41-3" aria-hidden="true" tabindex="-1"></a><span class="op">{</span></span> |
| 516 | <span id="cb41-4"><a href="#cb41-4" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> x <span class="op">=</span> <span class="dv">5</span><span class="op">;</span></span> | 736 | <span id="cb41-4"><a href="#cb41-4" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> x <span class="op">=</span> <span class="dv">5</span><span class="op">;</span></span> |
| 517 | <span id="cb41-5"><a href="#cb41-5" aria-hidden="true" tabindex="-1"></a> g <span class="op">=</span> v(x)<span class="op">;</span></span> | 737 | <span id="cb41-5"><a href="#cb41-5" aria-hidden="true" tabindex="-1"></a> g <span class="op">=</span> v(x)<span class="op">;</span></span> |
| 518 | <span id="cb41-6"><a href="#cb41-6" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span> | 738 | <span id="cb41-6"><a href="#cb41-6" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span> |
| 519 | <span id="cb41-7"><a href="#cb41-7" aria-hidden="true" tabindex="-1"></a><span class="pp">println!</span>(<span class="st">"{}"</span><span class="op">,</span> g(<span class="dv">2</span>))<span class="op">;</span></span></code></pre></div> | 739 | <span id="cb41-7"><a href="#cb41-7" aria-hidden="true" tabindex="-1"></a><span class="pp">println!</span>(<span class="st">"{}"</span><span class="op">,</span> g(<span class="dv">2</span>))<span class="op">;</span></span></code></pre></div> |
| 520 | <p>Variable <code>x</code> goes out of scope before <code>g</code> can return a concrete value. If we take ownership of <code>x</code> by <code>move</code>ing it into our closure, we can expect this to work reliably. In fact, rustc understands this, and forces you to use <code>move</code>.</p> | 740 | <p>Variable <code>x</code> goes out of scope before <code>g</code> can |
| 521 | <p>This usage of <code>move</code> is exactly why <strong>a curried function without a return is useless</strong>. 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.</p> | 741 | return a concrete value. If we take ownership of <code>x</code> by |
| 742 | <code>move</code>ing it into our closure, we can expect this to work | ||
| 743 | reliably. In fact, rustc understands this, and forces you to use | ||
| 744 | <code>move</code>.</p> | ||
| 745 | <p>This usage of <code>move</code> is exactly why <strong>a curried | ||
| 746 | function without a return is useless</strong>. Every variable we pass to | ||
| 747 | our curried function gets moved into its local scope. Playing with these | ||
| 748 | variables cannot cause a change outside this scope. Returning is our | ||
| 749 | only method of interaction with anything beyond this function.</p> | ||
| 522 | <h3 id="conclusion">Conclusion</h3> | 750 | <h3 id="conclusion">Conclusion</h3> |
| 523 | <p>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.</p> | 751 | <p>Currying may not seem to be all that useful. Curried functions are |
| 524 | <p>My original intention with <a href="https://peppe.rs">peppe.rs</a> was to post condensed articles, a micro blog, but this one turned out extra long.</p> | 752 | unwieldy in Rust because the standard library is not built around |
| 753 | currying. If you enjoy the possibilities posed by currying, consider | ||
| 754 | taking a look at Haskell or Scheme.</p> | ||
| 755 | <p>My original intention with <a href="https://peppe.rs">peppe.rs</a> | ||
| 756 | was to post condensed articles, a micro blog, but this one turned out | ||
| 757 | extra long.</p> | ||
| 525 | <p>Perhaps I should call it a ‘macro’ blog :)</p> | 758 | <p>Perhaps I should call it a ‘macro’ blog :)</p> |
| 526 | <section class="footnotes" role="doc-endnotes"> | 759 | <section id="footnotes" class="footnotes footnotes-end-of-document" |
| 760 | role="doc-endnotes"> | ||
| 527 | <hr /> | 761 | <hr /> |
| 528 | <ol> | 762 | <ol> |
| 529 | <li id="fn1" role="doc-endnote"><p><a href="https://doc.rust-lang.org/book/ch13-01-closures.html">https://doc.rust-lang.org/book/ch13-01-closures.html</a><a href="#fnref1" class="footnote-back" role="doc-backlink">↩︎</a></p></li> | 763 | <li id="fn1"><p><a |
| 530 | <li id="fn2" role="doc-endnote"><p><a href="https://caniuse.rs">caniuse.rs</a> contains an indexed list of features and their status.<a href="#fnref2" class="footnote-back" role="doc-backlink">↩︎</a></p></li> | 764 | href="https://doc.rust-lang.org/book/ch13-01-closures.html">https://doc.rust-lang.org/book/ch13-01-closures.html</a><a |
| 765 | href="#fnref1" class="footnote-back" role="doc-backlink">↩︎</a></p></li> | ||
| 766 | <li id="fn2"><p><a href="https://caniuse.rs">caniuse.rs</a> contains an | ||
| 767 | indexed list of features and their status.<a href="#fnref2" | ||
| 768 | class="footnote-back" role="doc-backlink">↩︎</a></p></li> | ||
| 531 | </ol> | 769 | </ol> |
| 532 | </section> | 770 | </section> |
| 533 | 771 | ||