fix erasure issues inside where clauses (add type to LetRec)

aoc2024/SortedMap.newt

@@ -57,19 +57,11 @@ updateMap k v (MapOf map) = case insertT23 k v map of
   Left map' => MapOf map'
   Right (a, b, c) => MapOf (Node2 a b c)
 
--- FIXME this doesn't work in a `where` because Letrec doesn't have the type
-toList' : ∀ k v h. T23 h k v → List (k × v) → List (k × v)
-toList' (Leaf k v) acc = (k, v) :: acc
-toList' (Node2 t1 k1 t2) acc = toList' t2 (toList' t1 acc)
-toList' (Node3 t1 k1 t2 k2 t3) acc = toList' t3 $ toList' t2 $ toList' t1 acc
-
 toList : ∀ k v. SortedMap k v → List (k × v)
-toList {k} {v} (MapOf smap) = reverse $ toList' smap Nil
-  -- FIXME erasure checking false positive (need type on foo in env when processing Letrec)
-  -- where
-  --   foo : ∀ k v h. T23 h k v → List (k × v) → List (k × v)
-  --   foo (Leaf k v) acc = (k, v) :: acc
-  --   foo (Node2 t1 k1 t2) acc = foo t2 (foo t1 acc)
-  --   foo (Node3 t1 k1 t2 k2 t3) acc = foo t3 $ foo t2 $ foo t1 acc
+toList {k} {v} (MapOf smap) = reverse $ go smap Nil
+  where
+    go : ∀ h. T23 h k v → List (k × v) → List (k × v)
+    go (Leaf k v) acc = (k, v) :: acc
+    go (Node2 t1 k1 t2) acc = go t2 (go t1 acc)
+    go (Node3 t1 k1 t2 k2 t3) acc = go t3 $ go t2 $ go t1 acc
 toList _ = Nil
-