enumerate

{-
Generate a list of numbers from `+0` up to but not including the specified
number

Examples:

```
./enumerate +10 = [ +0, +1, +2, +3, +4, +5, +6, +7, +8, +9 ]

./enumerate +0 = [] : List Natural
```
-}
    let enumerate
        : Natural → List Natural
        =   λ(n : Natural)
          → List/build
            Natural
            (   λ(list : Type)
              → λ(cons : Natural → list → list)
              → List/fold
                { index : Natural, value : {} }
                ( List/indexed
                  {}
                  ( List/build
                    {}
                    (   λ(list : Type)
                      → λ(cons : {} → list → list)
                      → Natural/fold n list (cons {=})
                    )
                  )
                )
                list
                (λ(x : { index : Natural, value : {} }) → cons x.index)
            )

in  enumerate