From 120b830cab1462d76761ee0d26cba7df783dc741 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sun, 5 Nov 2023 19:38:22 +0000
Subject: Check that handled effect is user-defined effect

---
 .../org/shedlang/compiler/typechecker/TypeChecker.java |  7 +++++++
 .../typechecker/errors/NotUserDefinedEffectError.java  | 18 ++++++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 src/main/java/org/shedlang/compiler/typechecker/errors/NotUserDefinedEffectError.java

(limited to 'src/main/java')

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index 29376e9f..f86ed78f 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -1593,6 +1593,13 @@ public class TypeChecker {
     ) {
         var typedHandledEffect = typeCheckEffect(untyped.handledEffect(), context);
 
+        if (!(typedHandledEffect.value() instanceof UserDefinedEffect)) {
+            throw new NotUserDefinedEffectError(
+                typedHandledEffect.value(),
+                untyped.handledEffect().source()
+            );
+        }
+
         var declaredVariables = DeclaredVariables.forFunctionStatements(
             untyped.body().statements(),
             P.vector()
diff --git a/src/main/java/org/shedlang/compiler/typechecker/errors/NotUserDefinedEffectError.java b/src/main/java/org/shedlang/compiler/typechecker/errors/NotUserDefinedEffectError.java
new file mode 100644
index 00000000..a740dccc
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/typechecker/errors/NotUserDefinedEffectError.java
@@ -0,0 +1,18 @@
+package org.shedlang.compiler.typechecker.errors;
+
+import org.shedlang.compiler.errors.SourceError;
+import org.shedlang.compiler.sources.Source;
+import org.shedlang.compiler.types.Effect;
+
+public class NotUserDefinedEffectError extends SourceError {
+    private final Effect effect;
+
+    public NotUserDefinedEffectError(Effect effect, Source source) {
+        super("Only user-defined effects can be handled, but was: " + effect.describe(), source);
+        this.effect = effect;
+    }
+
+    public Effect effect() {
+        return effect;
+    }
+}
-- 
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