unison/unison-src/transcripts/fix2712.md

```ucm:hide
.> builtins.merge
```

```unison
unique type Map k v = Tip | Bin Nat k v (Map k v) (Map k v)

mapWithKey : (k ->{e} a ->{e} b) -> Map k a ->{e} Map k b
mapWithKey f m = Tip
```

```ucm
.> add
```

```unison

naiomi = 
  susan: Nat ->{} Nat -> ()
  susan a b = ()
  
  pam: Map Nat Nat
  pam = Tip
  
  mapWithKey susan pam
  
```

```ucm
.> add
.> edit naiomi
.> undo
```

```ucm
.> load scratch.u
.> add
```