dhall-bhat/Compactable/bindOptional at 598e210a5688b049a8f081386b62db0d18a6a718 · FormationAI/dhall-bhat · GitHub

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{-

bindOptional binds to a `f` of Optional over the `f a` and `compact`s away the `None` values.

Examples:

```
    let replicate =
          https://raw.githubusercontent.com/dhall-lang/dhall-lang/master/Prelude/List/replicate

in  ./Compactable/bindOptional
    List
    ./List/compactable
    ./List/monad
    Natural
    Natural
    (   λ(n : Natural)
      →       if Natural/even n

        then  replicate n (Optional Natural) (Some n)

        else  [] : List (Optional Natural)
    )
    [ 0, 1, 2, 3, 4, 5 ]
= [ 2, 2, 4, 4, 4, 4 ]
```

-}
    let Monad = ./../Monad/Type

in    λ(f : Type → Type)
    → λ(c : ./Type f)
    → λ(monad : Monad f)
    → λ(a : Type)
    → λ(b : Type)
    → λ(k : a → f (Optional b))
    → λ(fa : f a)
    → ./compact f c b (monad.bind a (Optional b) fa k)