[Haskell-cafe] Feeding a monad into itself
jclites at mac.com
Fri Jul 21 02:16:15 UTC 2017
Also this pattern does seem Maybe-specific, in that for the general Monad case there's not an obvious termination condition.
> On Jul 20, 2017, at 11:03 AM, Rein Henrichs <rein.henrichs at gmail.com> wrote:
> This is about as good as you can do. The monad-loops package provides a variety of similar combinators, generally implemented in similar ways, but not this specific combinator. The downside of this combinator is that it is partial: it will run forever without producing anything if f never gives a Nothing.
>> On Thu, Jul 20, 2017 at 10:27 AM Jake <jake.waksbaum at gmail.com> wrote:
>> I have a function f :: a -> Maybe a that I want to feed into itself with some initial input until it returns Nothing.
>> untilNothing :: (a -> Maybe a) -> a -> a
>> untilNothing f x = case f x of
>> Just x' -> untilNothing f x'
>> Nothing -> x
>> Is there a better way to do this? I feel like there is something more general going on with Monads being fed into themselves, but maybe I'm wrong. Thoughts?
>> Haskell-Cafe mailing list
>> To (un)subscribe, modify options or view archives go to:
>> Only members subscribed via the mailman list are allowed to post.
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> Only members subscribed via the mailman list are allowed to post.
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Haskell-Cafe