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use proc_macro::TokenStream;
use quote::quote;
use syn::{Expr, Pat, Token, parse::{Parse, ParseStream, Result}, parse_macro_input};
struct ExternBlock {
pattern: Pat,
_arrow: Token![->],
return_ty: Expr,
_fat_arrow: Token![=>],
block: Expr,
_comma: Token![,],
}
struct ExternFunction {
function: syn::Ident,
blocks: Vec<ExternBlock>
}
impl Parse for ExternBlock {
fn parse(input: ParseStream) -> Result<Self> {
Ok(Self {
pattern: input.parse()?,
_arrow: input.parse()?,
return_ty: input.parse()?,
_fat_arrow: input.parse()?,
block: input.parse()?,
_comma: input.parse()?,
})
}
}
impl Parse for ExternFunction {
fn parse(input: ParseStream) -> Result<Self> {
let mut res = Self {
function: input.parse()?,
blocks: Vec::new(),
};
while !input.is_empty() {
res.blocks.push(input.parse()?);
}
Ok(res)
}
}
#[proc_macro]
pub fn extern_function(tokens: TokenStream) -> TokenStream {
let parsed: ExternFunction = parse_macro_input!(tokens);
let function = parsed.function;
let typecheck_blocks: Vec<_> = parsed.blocks.iter().map(|block| {
let pat = block.pattern.clone();
let ty = block.return_ty.clone();
quote! {
#pat => { Ok(sylt::Value::from(#ty)) }
}
}).collect();
let eval_blocks: Vec<_> = parsed.blocks.iter().map(|block| {
let pat = block.pattern.clone();
let expr = block.block.clone();
quote! {
#pat => #expr
}
}).collect();
let tokens = quote! {
pub fn #function (
__values: &[sylt::Value],
__typecheck: bool
) -> ::std::result::Result<sylt::Value, sylt::error::ErrorKind>
{
if __typecheck {
#[allow(unused_variables)]
match __values {
#(#typecheck_blocks),*
_ => Err(sylt::error::ErrorKind::ExternTypeMismatch(stringify!(#function).to_string(), __values.iter().map(|v| sylt::Type::from(v)).collect()))
}
} else {
match __values {
#(#eval_blocks),*
_ => Err(sylt::error::ErrorKind::ExternTypeMismatch(stringify!(#function).to_string(), __values.iter().map(|v| sylt::Type::from(v)).collect()))
}
}
}
};
TokenStream::from(tokens)
}
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