From 1c62effe91b5e50d1dbbc79c01655abfb3c17e16 Mon Sep 17 00:00:00 2001
From: David Li <li.davidm96@gmail.com>
Date: Sun, 5 Nov 2017 09:33:03 -0500
Subject: Check types in add expressions

---
 src/semantic/translate.rs | 43 ++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 40 insertions(+), 3 deletions(-)

diff --git a/src/semantic/translate.rs b/src/semantic/translate.rs
index 7bcd646..d3ebd2c 100644
--- a/src/semantic/translate.rs
+++ b/src/semantic/translate.rs
@@ -5,16 +5,21 @@ use super::types::Ty;
 #[derive(Debug)]
 pub enum TypeError {
     Unimplemented,
+    Mismatch {
+        expected: Ty,
+        actual: Ty,
+    },
 }
 
 type TypeEnvironment<'a> = environment::Environment<'a, String, Ty>;
 pub type Result = ::std::result::Result<Ty, WithLocation<TypeError>>;
 
 pub fn translate(program: &ast::Program) -> Result {
-    trans_exp(TypeEnvironment::new(None), &*program.0)
+    let mut env = TypeEnvironment::new(None);
+    trans_exp(&mut env, &*program.0)
 }
 
-fn trans_exp<'a>(venv: TypeEnvironment<'a>, exp: &WithLocation<ast::Expression>) -> Result {
+fn trans_exp<'a>(venv: &mut TypeEnvironment<'a>, exp: &WithLocation<ast::Expression>) -> Result {
     use ast::Expression::*;
 
     match &exp.value {
@@ -25,7 +30,39 @@ fn trans_exp<'a>(venv: TypeEnvironment<'a>, exp: &WithLocation<ast::Expression>)
             Err(WithLocation::new(TypeError::Unimplemented, exp.start, exp.end))
         },
         &BinOp(ref op, ref left, ref right) => {
-            Err(WithLocation::new(TypeError::Unimplemented, exp.start, exp.end))
+            use ast::BinOp::*;
+            match op {
+                &Add => {
+                    let left = trans_exp(venv, left)?;
+                    let right = trans_exp(venv, right)?;
+                    match (left, right) {
+                        (Ty::Int, Ty::Int) => {
+                            Ok(Ty::Int)
+                        }
+                        (Ty::String, Ty::String) => {
+                            Ok(Ty::String)
+                        }
+                        (Ty::Int, other) => {
+                            Err(WithLocation::new(TypeError::Mismatch {
+                                expected: Ty::Int,
+                                actual: other,
+                            }, exp.start, exp.end))
+                        }
+                        (Ty::String, other) => {
+                            Err(WithLocation::new(TypeError::Mismatch {
+                                expected: Ty::String,
+                                actual: other,
+                            }, exp.start, exp.end))
+                        }
+                        _ => {
+                            Err(WithLocation::new(TypeError::Unimplemented, exp.start, exp.end))
+                        }
+                    }
+                }
+                _ => {
+                    Err(WithLocation::new(TypeError::Unimplemented, exp.start, exp.end))
+                }
+            }
         },
         &Number(_) => Ok(Ty::Int),
         &String(_) => Ok(Ty::String),
-- 
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