On Tue, Oct 17, 2006 at 01:21:38PM -0300, V?ctor A. Rodr?guez wrote: > To: haskell-cafe@haskell.org > From: "Víctor A. Rodríguez" <[EMAIL PROTECTED]> > Date: Tue, 17 Oct 2006 13:21:38 -0300 > Subject: [Haskell-cafe] Newbie and working with IO Int and Int > > Hi all, > > I'm really newbie to Haskell, and working on a program I'm trying to make > some testing. > I make some test on certain know values ( e.g. adding 10 to 15 must return > 25) and some test on random values (eg. adding rnd1 to rnd2 must return > rnd1+rnd2). > > The problem that makes me mad is the random number generation. I can obtain > random numbers through module Random but all of them return IO Int values > (all I need are Ints) instead of Int. > I know that I can adjust my own functions to use IO Int instead of Int but > the call to certain functions must contain Int parameters, because these > ones can't be changed to accept IO Int (I read > http://haskell.org/hawiki/ThatAnnoyingIoType and know that can convert from > IO Int to Int :-P). > > How can I deal with this problem ??
you should probably keep reading on. (-: have you seen the stuff on the new wiki? http://www.haskell.org/haskellwiki/Books_and_tutorials#Using_monads short answer: the type IO Int describes computations that yield integers, and in order to get to the Int you need to run the computation. if you have a pure function f and want to feed it with random values, you need to do something like: randomIO >>= \ x -> randomIO >>= \ y -> return (f x y) the complete expression has type IO Int again. don't try to strip off that IO; there are ways, but they don't teach you how to do it right. hth, m.
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