[Haskell-cafe] Missing common function for Maybe types

[David Feuer]

Your code doesn't type check and there is no way to write a total function
with the type of foobar. What are you actually trying to do? Why do you say
this is "common"?

On Tue, Jul 31, 2018, 3:07 AM Marc Busqué <marc at lamarciana.com> wrote:

> Hi!
>
> I have two functions:
>
> ```
> foo :: a -> Maybe b
> bar :: a -> Maybe c
> ```
>
> From which I want to build a higher order function:
>
> ```
> foobar :: a -> (a -> Maybe b) -> (a -> Maybe c) -> Either b c
> ```
>
> The implementation I need is:
>
> ```
> foobar x f g =
>    case (f x) of
>      Nothing -> g x
>      Just y  -> Just y
> ```
>
> I'm a bit surprised that looking at hoogle I don't find a built-in
> solution for this quite common need for `Maybe` types (or perhaps for
> any monad).
>
> Am I looking in the wrong way? Does it exist a similar abstraction but
> with a different shape?
>
> Thanks in advance,
>
> Marc Busqué
> http://waiting-for-dev.github.io/about/
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