Check for duplicate named params in function type

1 files changed, 10 insertions, 0 deletions

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index 3dd5e138..d7ad4627 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -651,6 +651,16 @@ public class TypeChecker {
             })
             .toList();
 
+        var seenParamNames = new HashSet<String>();
+        for (var untypedParamNode : untyped.params().named()) {
+            if (!seenParamNames.add(untypedParamNode.name())) {
+                throw new DuplicateVariableName(
+                    untypedParamNode.name(),
+                    untypedParamNode.source()
+                );
+            }
+        }
+
         var effect = untyped.effect()
             .map(untypedEffect -> typeCheckTypeLevelExpression(
                 TypeSets.EFFECT,