Herbert Valerio actually pointed out to me in PVT that funnily enough
I've actually *forgotten* and *rediscovered* this idiom! =)
http://www.haskell.org/pipermail/libraries/2011-November/017257.html
Cheers!
On Sat, Jan 26, 2013 at 5:43 PM, Felipe Almeida Lessa
felipe.le...@gmail.com wrote:
Hey,
Just wanted to share this little insight I had that I don't think is a
common idiom. Often times I need to define:
whenJust :: Monad m = Maybe a - (a - m b) - m ()
whenJust (Just x) f = f x
whenJust Nothing _ = return ()
It always bugged me that you can't find this function anywhere.
Actually, you can find it on at least a couple of packages [1], but
you can't find it on a standard place. Or can you?
A few days ago I decided to hoogle the type of whenJust [2] and what I
discovered is that
import Data.Foldable (forM_)
whenJust = forM_
For example, instead of:
mfoo - doSomething
case mfoo of
Just foo - ...
Nothing - return ()
You may just write:
forM_ mfoo $ \foo -
...
There you go. I hope this is useful to someone =).
Cheers,
[1] http://holumbus.fh-wedel.de/hayoo/hayoo.html?query=whenJust
[2]
http://www.haskell.org/hoogle/?hoogle=Maybe%20a%20-%3E%20(a%20-%3E%20m%20b)%20-%3E%20m%20()
--
Felipe.
--
Felipe.
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