``` unison
structural type Foo f
  = Foo (f ())
unique type Baz = Baz (Foo Bar)

unique type Bar 
  = Bar Baz
```

``` ucm

  Loading changes detected in scratch.u.

  Kind mismatch arising from
        3 | unique type Baz = Baz (Foo Bar)
    
    Foo expects an argument of kind: Type -> Type; however, it
    is applied to Bar which has kind: Type.

```