From b1ef87bc10b662d6e37f929fa86db7a20b44e7dd Mon Sep 17 00:00:00 2001
From: David Li <li.davidm96@gmail.com>
Date: Mon, 6 Nov 2017 20:49:04 -0500
Subject: Typecheck function declarations

---
 src/semantic/translate.rs | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/semantic/translate.rs b/src/semantic/translate.rs
index 7e0d2b8..617c832 100644
--- a/src/semantic/translate.rs
+++ b/src/semantic/translate.rs
@@ -64,8 +64,30 @@ fn trans_decl<'a>(
     tenv: &mut TypeEnvironment<'a>,
     decl: &WithLocation<ast::Declaration>) -> Result {
     match decl.declaration {
-        ast::DeclarationBody::Fun { .. } => {
-            err!(decl, TypeError::Unimplemented)
+        ast::DeclarationBody::Fun { ref ty, ref params, ref body } => {
+            let declared_ty = if let &Some(ref ty) = ty {
+                Some(ast::WithLocation::new(trans_ty(venv, tenv, &ty)?, ty.start, ty.end))
+            } else { None };
+
+            let mut new_venv = TypeEnvironment::new(Some(venv));
+            let mut new_tenv = TypeEnvironment::new(Some(tenv));
+            for param in params.iter() {
+                let decl_ty = trans_ty(&mut new_venv, &mut new_tenv, &param.ty)?;
+                new_venv.add_binding(param.name.value.clone(), decl_ty);
+            }
+
+            let body_ty = trans_exp(&mut new_venv, &mut new_tenv, &*body)?;
+
+            if let Some(decl_ty) = declared_ty {
+                if &decl_ty.value != &body_ty {
+                    return err!(decl_ty, TypeError::Mismatch {
+                        expected: decl_ty.value,
+                        actual: body_ty,
+                    });
+                }
+            }
+
+            Ok(body_ty)
         }
         ast::DeclarationBody::Ty { ref ty } => {
             trans_ty(venv, tenv, ty)
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