1 files changed, 87 insertions, 0 deletions
diff --git a/sylt_macro/src/lib.rs b/sylt_macro/src/lib.rs
new file mode 100644
index 0000000..241ef7d
--- /dev/null
+++ b/sylt_macro/src/lib.rs
@@ -0,0 +1,87 @@
+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(#ty.as_value()) }
+        }
+    }).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)
+}