Your `foobar` function cannot work, it doesn't handle the case when the URL is neither http nor https. I would use catMaybes and headMay to work this out...untested code, and you'll need the `safe` library for headMay too... parse :: ByteString -> Maybe (Url Http, Option scheme) parse input = headMay $ catMaybes $ fmap input [parseUrlHttp, parseUrlHttps] And everything is lazy so if the input gets parsed correctly by the first call you never actually perform the second one.... n On 31/07/18 08:07, 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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