[Haskell-beginners] Ignoring the result of a monadic computation
magnus at therning.org
Fri Nov 19 10:26:04 EST 2010
On Fri, Nov 19, 2010 at 15:21, Brent Yorgey <byorgey at seas.upenn.edu> wrote:
> On Fri, Nov 19, 2010 at 07:56:02AM +0100, Tim Baumgartner wrote:
>> while learning about monads, I had something like
>> line <- getLine
>> putStrLn line
>> and I wondered if I could write it in one line, without naming of parameters.
>> I finally came up with
>> getLine >>= ignore something >>= putStrLn
>> ignore :: Monad m => m a -> b -> m b
>> ignore m a = m >> return a
>> I'm satisfied with this solution but searching hoogle I didn't find
>> a standard function for my ignore. Am I missing something?
> Nope, there isn't such a function, but I like it. It reminds me of
> (*>) and (<*) from Control.Applicative. Note that you sometimes see
> the name 'ignore' used for a slightly different function, namely
> ignore :: Monad m => m a -> m ()
> ignore m = m >> return ()
> but yours is a bit more general. Other names for your function might
> be 'passThrough' or something like that.
I'm not sure I see any benefit of ': m a -> b -> m b' over 'm a -> m
()'. When would you want to use the former?
Magnus Therning (OpenPGP: 0xAB4DFBA4)
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