Change List.mapM' to avoid leaving functions around

1 files changed, 3 insertions, 3 deletions

diff --git a/lib/ur/list.ur b/lib/ur/list.ur
index 2ee60538..7079f6bc 100644
--- a/lib/ur/list.ur
+++ b/lib/ur/list.ur
@@ -44,8 +44,8 @@ fun mapM (m ::: (Type -> Type)) (_ : monad m) (a ::: Type) (b ::: Type) f =
     let
         fun mapM' acc ls =
             case ls of
-                [] => acc
-              | x :: ls => mapM' (x' <- f x; ls' <- acc; return (x' :: ls')) ls
+                [] => return (rev acc)
+              | x :: ls => x' <- f x; mapM' (x' :: acc) ls
     in
-        mapM' (return [])
+        mapM' []
     end