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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;
}
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