Type check integer subtraction

2 files changed, 15 insertions, 2 deletions

diff --git a/src/main/java/org/shedlang/compiler/ast/untyped/UntypedBinaryOperator.java b/src/main/java/org/shedlang/compiler/ast/untyped/UntypedBinaryOperator.java
index 0a14b547..f08febfa 100644
--- a/src/main/java/org/shedlang/compiler/ast/untyped/UntypedBinaryOperator.java
+++ b/src/main/java/org/shedlang/compiler/ast/untyped/UntypedBinaryOperator.java
@@ -1,5 +1,6 @@
 package org.shedlang.compiler.ast.untyped;
 
 public enum UntypedBinaryOperator {
-    ADD
+    ADD,
+    SUB
 }
diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index d3d0ef81..b4c3983e 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -157,15 +157,27 @@ public class TypeChecker {
         var rightResult = typeCheckExpression(untyped.right(), context);
         var right = rightResult.value();
         context = rightResult.context();
+        
+        var operator = typeCheckBinaryOperator(untyped.operator(), left.type(), right.type());
 
         return context.toResult(new TypedBinaryOperationNode(
-            TypedBinaryOperator.INT_ADD,
+            operator,
             left,
             right,
             untyped.source()
         ));
     }
 
+    private static TypedBinaryOperator typeCheckBinaryOperator(UntypedBinaryOperator operator, Type left, Type right) {
+        return switch (operator) {
+            case ADD ->
+                TypedBinaryOperator.INT_ADD;
+
+            case SUB ->
+                TypedBinaryOperator.INT_SUB;
+        };
+    }
+
     public static TypeCheckerResult<TypedExpressionNode> typeCheckBoolLiteral(
         UntypedBoolLiteralNode untyped,
         TypeCheckerContext context