1 files changed, 10 insertions, 3 deletions
diff --git a/src/main/java/org/shedlang/compiler/types/TypeSubstitution.java b/src/main/java/org/shedlang/compiler/types/TypeSubstitution.java
index e08b859e..7f86b3ef 100644
--- a/src/main/java/org/shedlang/compiler/types/TypeSubstitution.java
+++ b/src/main/java/org/shedlang/compiler/types/TypeSubstitution.java
@@ -13,9 +13,16 @@ public class TypeSubstitution {
                 throw new UnsupportedOperationException("TODO");
             }
 
-            case FunctionType functionType -> {
-                throw new UnsupportedOperationException("TODO");
-            }
+            case FunctionType functionType -> new FunctionType(
+                functionType.positionalParams().stream()
+                    .map(param -> substitute(param, map))
+                    .toList(),
+                functionType.namedParams().stream()
+                    .map(param -> new NamedParam(param.name(), substitute(param.type(), map)))
+                    .toList(),
+                functionType.effect(),
+                substitute(functionType.returnType(), map)
+            );
 
             case IntType intType -> type;