You can use 'when' or 'unless' from the module Control.Monad, but they
each have only one branch, see:
http://members.chello.nl/hjgtuyl/tourdemonad.html#unless
and
http://members.chello.nl/hjgtuyl/tourdemonad.html#when
You can create a monadic 'if' like this (in an interactive session):
Control.Monad> let ifM p a b = do { p' <- p; if p' then return a else
return b } in ifM (Just True) 1 2
Just 1
Met vriendelijke groet,
Henk-Jan van Tuyl
--
On Thu, 23 Nov 2006 22:34:49 +0100, Dougal Stanton <[EMAIL PROTECTED]>
wrote:
Is there some sort of equivalent of the if/then/else construct for use
in the IO monad? For instance the following can get quite tedious:
do bool <- doesFileExist filename
if bool
then sth
else sth'
Is there a more compact way of writing that? Something akin to:
condM (doesFileExist filename) (sth) (sth')
Or maybe there's a more sensible way of doing the above that I've
missed. I seem to use endless alternate conditions sometimes and there's
bound to be a better way.
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