I just wanted to say thanks to everyone that helped me on this. I'm still reading/cogitating the stuff you gave me, but I did manage to write a Fisher-Yates shuffle using random numbers. I had a lightbulb moment while reading about sequence (so I suppose that might count as my 7th Monad tutorial :). The <- takes values out of monads[1]. So simple! -- let c = [11..18] --shuff (length c) c shuff :: Int -> [a] -> IO [a] shuff 0 xs = return xs shuff (len + 1) xs = (rand 1 (len + 1)) >>= \r -> shuff len $ requeue r xs where requeue = \z xs -> (init $ take z xs) ++ (drop z xs) ++ [last $ take z xs] rand :: Int -> Int -> IO Int rand low high = getStdRandom (randomR (low,high)) Since it's recursive I suspect there may be a way to do this with a fold, but I'll probably work that out at a later lightbulb moment (after more questions:) Thanks again. Iain [1] In a lot of IO tutorials it just seems to be the 'do' syntax for assigning a value to a symbol, but of course, :t getLine getLine :: IO String On 24 Sep 2008, at 10:03 pm, Iain Barnett wrote:
Hi,
I have a function, that produces a random number between two given numbers
rand :: Int -> Int -> IO Int rand low high = getStdRandom (randomR (low,high))
(Naively) I'd like to write something like
take (rand 1 10 ) [1..10]
and see [1,2,3,4] ... or anything but nasty type-error messages.
I'm reading about 6 tutorials on monads simultaneously but still can't crack this simple task, and won't pain you with all the permutations of code I've already tried. It's a lot, and it ain't pretty.
Would anyone be able to break away from C/C++ vs Haskell to help? Just a point in the right direction or a good doc to read, anything that helps will be much appreciated.
Regards Iain