3 files changed, 116 insertions, 1 deletions

diff --git a/.gitignore b/.gitignore
index 088ba6b..83c440c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,6 @@
 # Generated by Cargo
 # will have compiled files and executables
-/target/
+**/target/**
 
 # Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
 # More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..bb0fb84
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,18 @@
+[package]
+name = "currying"
+version = "0.1.0"
+authors = ["Akshay <[email protected]>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+proc-macro2 = "1.0.9"
+quote = "1.0"
+
+[dependencies.syn]
+version = "1.0"
+features = ["full"]
+
+[lib]
+proc-macro = true
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..8a030c4
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,97 @@
+extern crate proc_macro;
+
+use proc_macro::TokenStream;
+use quote::{format_ident, quote};
+use syn::punctuated::Punctuated;
+use syn::{parse_macro_input, Block, FnArg, ItemFn, Pat, ReturnType, Type};
+
+#[proc_macro_attribute]
+pub fn curry(_attr: TokenStream, item: TokenStream) -> TokenStream {
+    let parsed = parse_macro_input!(item as ItemFn);
+    generate_curry(parsed).into()
+}
+
+fn extract_type(a: FnArg) -> Box<Type> {
+    match a {
+        FnArg::Typed(p) => p.ty,
+        _ => panic!("Not supported on types with `self`!"),
+    }
+}
+
+fn extract_arg_pat(a: FnArg) -> Box<Pat> {
+    match a {
+        FnArg::Typed(p) => p.pat,
+        _ => panic!("Not supported on types with `self`!"),
+    }
+}
+
+fn extract_return_type(a: ReturnType) -> Box<Type> {
+    match a {
+        ReturnType::Type(_, p) => p,
+        _ => panic!("Not supported on functions without return types!"),
+    }
+}
+
+fn extract_arg_types(fn_args: Punctuated<FnArg, syn::token::Comma>) -> Vec<Box<Type>> {
+    return fn_args.into_iter().map(extract_type).collect::<Vec<_>>();
+}
+
+fn extract_arg_idents(fn_args: Punctuated<FnArg, syn::token::Comma>) -> Vec<Box<Pat>> {
+    return fn_args.into_iter().map(extract_arg_pat).collect::<Vec<_>>();
+}
+
+fn generate_type_aliases(
+    fn_arg_types: &[Box<Type>],
+    fn_return_type: Box<Type>,
+    fn_name: &syn::Ident,
+) -> Vec<proc_macro2::TokenStream> {
+    let type_t0 = format_ident!("_{}_T0", fn_name);
+    let mut type_aliases = vec![quote! { type #type_t0 = #fn_return_type }];
+    for (i, t) in (1..).zip(fn_arg_types.into_iter().rev()) {
+        let p = format_ident!("_{}_{}", fn_name, format!("T{}", i - 1));
+        let n = format_ident!("_{}_{}", fn_name, format!("T{}", i));
+        type_aliases.push(quote! {
+            type #n = impl Fn(#t) -> #p
+        })
+    }
+    return type_aliases;
+}
+
+fn generate_body(fn_args: &[Box<Pat>], body: Box<Block>) -> proc_macro2::TokenStream {
+    quote! {
+        return #( move |#fn_args| )* #body
+    }
+}
+
+fn generate_curry(parsed: ItemFn) -> proc_macro2::TokenStream {
+    let fn_body = parsed.block;
+    let sig = parsed.sig;
+    let vis = parsed.vis;
+    let fn_name = sig.ident;
+    let fn_args = sig.inputs;
+    let fn_return_type = sig.output;
+
+    let arg_idents = extract_arg_idents(fn_args.clone());
+    let first_ident = &arg_idents.first().unwrap();
+    let curried_body = generate_body(&arg_idents[1..], fn_body.clone());
+
+    let arg_types = extract_arg_types(fn_args.clone());
+    let first_type = &arg_types.first().unwrap();
+    let type_aliases = generate_type_aliases(
+        &arg_types[1..],
+        extract_return_type(fn_return_type),
+        &fn_name,
+    );
+
+    let return_type = format_ident!("_{}_{}", &fn_name, format!("T{}", type_aliases.len() - 1));
+
+    let gen = quote! {
+        #(#type_aliases);* ;
+        #vis fn #fn_name (#first_ident: #first_type) -> #return_type {
+            #curried_body ;
+        }
+    };
+
+    println!("{}", gen);
+    return gen;
+}