```ucm:hide
scratch/main> 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
scratch/main> add
```

```unison

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