Type-check string addition

3 files changed, 14 insertions, 11 deletions

diff --git a/src/main/java/org/shedlang/compiler/ast/typed/TypedBinaryOperator.java b/src/main/java/org/shedlang/compiler/ast/typed/TypedBinaryOperator.java
index 38d628fa..2f2e5929 100644
--- a/src/main/java/org/shedlang/compiler/ast/typed/TypedBinaryOperator.java
+++ b/src/main/java/org/shedlang/compiler/ast/typed/TypedBinaryOperator.java
@@ -7,7 +7,8 @@ public enum TypedBinaryOperator {
     INT_ADD(Types.INT),
     INT_EQUALS(Types.BOOL),
     INT_NOT_EQUAL(Types.BOOL),
-    INT_SUB(Types.INT);
+    INT_SUB(Types.INT),
+    STRING_ADD(Types.STRING);
 
     private final Type type;
 
diff --git a/src/main/java/org/shedlang/compiler/stackir/StackCompiler.java b/src/main/java/org/shedlang/compiler/stackir/StackCompiler.java
index b6aec8dd..6bda0b6d 100644
--- a/src/main/java/org/shedlang/compiler/stackir/StackCompiler.java
+++ b/src/main/java/org/shedlang/compiler/stackir/StackCompiler.java
@@ -24,6 +24,8 @@ public class StackCompiler {
                     new IntNotEqualInstruction(node.source());
                 case INT_SUB ->
                     new IntSubInstruction(node.source());
+                case STRING_ADD ->
+                    throw new UnsupportedOperationException("TODO");
             });
     }
 
diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index db7becc3..273f1898 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -181,21 +181,21 @@ public class TypeChecker {
     ) {
         if (left.equals(Types.INT) && right.equals(Types.INT)) {
             return switch (operator) {
-                case ADD ->
-                    TypedBinaryOperator.INT_ADD;
+                case ADD -> TypedBinaryOperator.INT_ADD;
 
-                case EQUALS ->
-                    TypedBinaryOperator.INT_EQUALS;
+                case EQUALS -> TypedBinaryOperator.INT_EQUALS;
 
-                case NOT_EQUAL ->
-                    TypedBinaryOperator.INT_NOT_EQUAL;
+                case NOT_EQUAL -> TypedBinaryOperator.INT_NOT_EQUAL;
 
-                case SUB ->
-                    TypedBinaryOperator.INT_SUB;
+                case SUB -> TypedBinaryOperator.INT_SUB;
             };
-        } else {
-            throw new UnsupportedBinaryOperationError(operator, left, right, source);
+        } else if (left.equals(Types.STRING) && right.equals(Types.STRING)) {
+            if (operator == UntypedBinaryOperator.ADD) {
+                return TypedBinaryOperator.STRING_ADD;
+            }
         }
+
+        throw new UnsupportedBinaryOperationError(operator, left, right, source);
     }
 
     public static TypeCheckerResult<TypedExpressionNode> typeCheckBoolLiteral(