``` unison
structural type Foo = MkFoo Nat

main : () -> Foo
main _ = MkFoo 5
```

``` ucm

  Loading changes detected in scratch.u.

  I found and typechecked these definitions in scratch.u. If you
  do an `add` or `update`, here's how your codebase would
  change:
  
    ⍟ These new definitions are ok to `add`:
    
      structural type Foo
      main : 'Foo

```
``` ucm
foo/main> add

  ⍟ I've added these definitions:
  
    structural type Foo
    main : 'Foo

foo/main> run main

  MkFoo 5

```