[Haskell-cafe] Missing common function for Maybe types

Vanessa McHale vanessa.mchale at iohk.io
Tue Jul 31 11:39:16 UTC 2018

That doesn't exactly make sense. You'd need two versions of that
function in all likelihood - one left-biased and another right-biased.

On 07/31/2018 02:07 AM, Marc Busqué 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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*Vanessa McHale*
Functional Compiler Engineer | Chicago, IL

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