So, the next question is: Why isn't this already in Control.Monad?
On Mar 21, 2007, at 8:27 AM, Jules Bean wrote:
David F. Place wrote:
Interesting, but what if 'p' is also a monadic action? For
instance, it might access the state of the State monad which 'f'
is updating.
Then I'd stop trying to do it as a one-liner, I suspect:
let untilM p f x = do
cond <- p x
if cond then return x
else do y <- f x
untilM p f y
On Mar 21, 2007, at 5:31 AM, Jules Bean wrote:
..but here 'f' is a pure function, not a monadic action. If you
want f to be a monadic action then you want:
*Main> :t let untilM p f x = if p x then return x else untilM p f
=<< f x in untilM
let untilM p f x = if p x then return x else untilM p f =<< f x
in untilM :: (Monad m) => (a -> Bool) -> (a -> m a) -> a -> m a
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David F. Place
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David F. Place
mailto:[EMAIL PROTECTED]
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