Re: [Haskell-cafe] Feeding a monad into itself

Also this pattern does seem Maybe-specific, in that for the general Monad case there's not an obvious termination condition. JEff

On Jul 20, 2017, at 11:03 AM, Rein Henrichs 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.

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On Thu, Jul 20, 2017 at 10:27 AM Jake 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: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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