Disallow returns in effect handlers

3 files changed, 21 insertions, 0 deletions

diff --git a/src/main/java/org/shedlang/compiler/typechecker/ReturnTypeState.java b/src/main/java/org/shedlang/compiler/typechecker/ReturnTypeState.java
index bb96cfa7..b43b17ea 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/ReturnTypeState.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/ReturnTypeState.java
@@ -14,8 +14,13 @@ public sealed interface ReturnTypeState {
         return new ImplicitLowerBound(type);
     }
 
+    static ReturnTypeState effectHandler(Type resumeType) {
+        return new EffectHandler(resumeType);
+    }
+
     record NotInFunction() implements ReturnTypeState {}
     record Explicit(Type type) implements ReturnTypeState {}
     record ImplicitUnknown() implements ReturnTypeState {}
     record ImplicitLowerBound(Type type) implements ReturnTypeState {}
+    record EffectHandler(Type resumeType) implements ReturnTypeState {}
 }
diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index 4cf49b47..756e4584 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -618,6 +618,9 @@ public class TypeChecker {
                 // TODO: better error
                 throw new IllegalStateException();
             }
+            case ReturnTypeState.EffectHandler effectHandler -> {
+                returnType = effectHandler.resumeType();
+            }
         }
 
         // TODO: get free variables on exit?
@@ -847,6 +850,9 @@ public class TypeChecker {
                 // reasonable error.
                 throw new CannotReturnOutsideOfFunctionError(returnValueSource);
             }
+            case ReturnTypeState.EffectHandler effectHandler -> {
+                throw new CannotReturnFromEffectHandlerFieldError(returnValueSource);
+            }
         };
 
         return context;
diff --git a/src/main/java/org/shedlang/compiler/typechecker/errors/CannotReturnFromEffectHandlerFieldError.java b/src/main/java/org/shedlang/compiler/typechecker/errors/CannotReturnFromEffectHandlerFieldError.java
new file mode 100644
index 00000000..e887f353
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/typechecker/errors/CannotReturnFromEffectHandlerFieldError.java
@@ -0,0 +1,10 @@
+package org.shedlang.compiler.typechecker.errors;
+
+import org.shedlang.compiler.errors.SourceError;
+import org.shedlang.compiler.sources.Source;
+
+public class CannotReturnFromEffectHandlerFieldError extends SourceError {
+    public CannotReturnFromEffectHandlerFieldError(Source source) {
+        super("Cannot return from effect handler field", source);
+    }
+}