Throw NoSuchMethod when method doesn't exist

3 files changed, 24 insertions, 1 deletions

diff --git a/src/main/java/org/zwobble/couscous/interpreter/NoSuchMethod.java b/src/main/java/org/zwobble/couscous/interpreter/NoSuchMethod.java
new file mode 100644
index 0000000..e69c978
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/interpreter/NoSuchMethod.java
@@ -0,0 +1,12 @@
+package org.zwobble.couscous.interpreter;
+
+import lombok.EqualsAndHashCode;
+import lombok.Value;
+
+@Value
+@EqualsAndHashCode(callSuper=false)
+public class NoSuchMethod extends InterpreterException {
+    private static final long serialVersionUID = 1L;
+
+    String methodName;
+}
diff --git a/src/main/java/org/zwobble/couscous/values/StringValue.java b/src/main/java/org/zwobble/couscous/values/StringValue.java
index 3a1a13d..9cf81ff 100644
--- a/src/main/java/org/zwobble/couscous/values/StringValue.java
+++ b/src/main/java/org/zwobble/couscous/values/StringValue.java
@@ -2,6 +2,8 @@ package org.zwobble.couscous.values;
 
 import java.util.List;
 
+import org.zwobble.couscous.interpreter.NoSuchMethod;
+
 import lombok.Value;
 import lombok.val;
 
@@ -18,7 +20,7 @@ public class StringValue implements InterpreterValue {
             val endIndex = (IntegerValue)arguments.get(1);
             return new StringValue(value.substring(startIndex.getValue(), endIndex.getValue()));
         } else {
-            throw new UnsupportedOperationException();
+            throw new NoSuchMethod(methodName);
         }
     }
 }
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 442c6e9..ee4f700 100644
--- a/src/test/java/org/zwobble/couscous/tests/interpreter/EvaluatorTests.java
+++ b/src/test/java/org/zwobble/couscous/tests/interpreter/EvaluatorTests.java
@@ -5,6 +5,7 @@ import org.zwobble.couscous.ast.FormalArgumentNode;
 import org.zwobble.couscous.ast.TernaryConditionalNode;
 import org.zwobble.couscous.interpreter.ConditionMustBeBoolean;
 import org.zwobble.couscous.interpreter.Environment;
+import org.zwobble.couscous.interpreter.NoSuchMethod;
 import org.zwobble.couscous.values.IntegerValue;
 import org.zwobble.couscous.values.StringValue;
 
@@ -64,6 +65,14 @@ public class EvaluatorTests {
         assertEquals(new StringValue("ell"), result);
     }
     
+    @Test
+    public void errorIfMethodDoesNotExist() {
+        val exception = assertThrows(NoSuchMethod.class,
+            () -> eval(emptyEnvironment(),
+                methodCall(literal("hello"), "size")));
+        assertEquals(new NoSuchMethod("size"), exception);
+    }
+    
     private static Environment emptyEnvironment() {
         return new Environment(ImmutableMap.of());
     }