Some basics:

``` unison
unique type Cat.Dog = Mouse Nat
unique type Rat.Dog = Bird

countCat = cases
  Cat.Dog.Mouse x -> Bird
```

``` ucm
scratch/main> add

  ⍟ I've added these definitions:
  
    type Cat.Dog
    type Rat.Dog
    countCat : Cat.Dog -> Rat.Dog

```
Now I want to add a constructor.

``` unison
unique type Rat.Dog = Bird | Mouse
```

``` ucm
scratch/main> update

  Okay, I'm searching the branch for code that needs to be
  updated...

  That's done. Now I'm making sure everything typechecks...

  Everything typechecks, so I'm saving the results...

  Done.

```