Implements casts in the interpreter

4 files changed, 50 insertions, 6 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;
+    }
+}
diff --git a/src/test/java/org/zwobble/couscous/tests/interpreter/EvaluatorTests.java b/src/test/java/org/zwobble/couscous/tests/interpreter/EvaluatorTests.java
index d3c2a12..4d91cdb 100644
--- a/src/test/java/org/zwobble/couscous/tests/interpreter/EvaluatorTests.java
+++ b/src/test/java/org/zwobble/couscous/tests/interpreter/EvaluatorTests.java
@@ -1,8 +1,6 @@
 package org.zwobble.couscous.tests.interpreter;
 
-import java.util.List;
-import java.util.Optional;
-
+import com.google.common.collect.ImmutableMap;
 import org.junit.Test;
 import org.zwobble.couscous.ast.ClassNode;
 import org.zwobble.couscous.ast.ExpressionNode;
@@ -14,14 +12,17 @@ import org.zwobble.couscous.interpreter.values.InterpreterValue;
 import org.zwobble.couscous.interpreter.values.StringInterpreterValue;
 import org.zwobble.couscous.tests.BackendEvalTests;
 import org.zwobble.couscous.values.IntegerValue;
+import org.zwobble.couscous.values.ObjectValues;
 import org.zwobble.couscous.values.PrimitiveValue;
 import org.zwobble.couscous.values.StringValue;
 
-import com.google.common.collect.ImmutableMap;
+import java.util.List;
+import java.util.Optional;
 
 import static org.junit.Assert.assertEquals;
 import static org.zwobble.couscous.ast.AssignmentNode.assign;
 import static org.zwobble.couscous.ast.AssignmentNode.assignStatement;
+import static org.zwobble.couscous.ast.CastNode.cast;
 import static org.zwobble.couscous.ast.ConstructorCallNode.constructorCall;
 import static org.zwobble.couscous.ast.FieldAccessNode.fieldAccess;
 import static org.zwobble.couscous.ast.FormalArgumentNode.formalArg;
@@ -186,6 +187,23 @@ public class EvaluatorTests extends BackendEvalTests {
         
         assertEquals(new UnexpectedValueType(IntegerValue.REF, StringValue.REF), exception);
     }
+
+    @Test
+    public void validCastPassesValueThrough() {
+        InterpreterValue value = eval(
+            emptyEnvironment(),
+            cast(literal("42"), ObjectValues.OBJECT));
+        assertEquals(value("42"), value);
+    }
+
+    @Test
+    public void errorIfCastIsNotValid() {
+        InvalidCast exception = assertThrows(InvalidCast.class,
+            () -> eval(emptyEnvironment(),
+                cast(literal(42), StringValue.REF)));
+        assertEquals(StringValue.REF, exception.getExpected());
+        assertEquals(IntegerValue.REF, exception.getActual());
+    }
     
     private static Environment emptyEnvironment() {
         return new Environment(