3 files changed, 28 insertions, 2 deletions
diff --git a/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java b/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java
index d90b78b..56ccca7 100644
--- a/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java
+++ b/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java
@@ -125,7 +125,11 @@ public class Evaluator implements ExpressionNodeMapper<InterpreterValue> {
 
     @Override
     public InterpreterValue visit(CastNode cast) {
-        throw new UnsupportedOperationException();
+        InterpreterValue value = eval(cast.getExpression());
+        if (!InterpreterTypes.isSubType(cast.getType(), value.getType())) {
+            throw new InvalidCast(cast.getType(), value.getType().getName());
+        }
+        return value;
     }
 
     private static boolean isIntegerBox(TypeCoercionNode typeCoercion) {
diff --git a/src/main/java/org/zwobble/couscous/interpreter/InterpreterTypes.java b/src/main/java/org/zwobble/couscous/interpreter/InterpreterTypes.java
index 1e644c8..71f875d 100644
--- a/src/main/java/org/zwobble/couscous/interpreter/InterpreterTypes.java
+++ b/src/main/java/org/zwobble/couscous/interpreter/InterpreterTypes.java
@@ -16,7 +16,7 @@ public class InterpreterTypes {
         }
     }
 
-    private static boolean isSubType(TypeName superTypeName, ConcreteType subType) {
+    public static boolean isSubType(TypeName superTypeName, ConcreteType subType) {
         return
             superTypeName.equals(subType.getName()) ||
             superTypeName.equals(ObjectValues.OBJECT) ||
diff --git a/src/main/java/org/zwobble/couscous/interpreter/InvalidCast.java b/src/main/java/org/zwobble/couscous/interpreter/InvalidCast.java
new file mode 100644
index 0000000..1d89ad1
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/interpreter/InvalidCast.java
@@ -0,0 +1,22 @@
+package org.zwobble.couscous.interpreter;
+
+import org.zwobble.couscous.ast.TypeName;
+
+public class InvalidCast extends RuntimeException {
+    private final TypeName expected;
+    private final TypeName actual;
+
+    public InvalidCast(TypeName expected, TypeName actual) {
+
+        this.expected = expected;
+        this.actual = actual;
+    }
+
+    public TypeName getExpected() {
+        return expected;
+    }
+
+    public TypeName getActual() {
+        return actual;
+    }
+}