Re: [Haskell-cafe] Convert IO Int to Int

9 Jun 2009

      Am Dienstag 09 Juni 2009 15:57:24 schrieb Magnus Therning:
...
On Tue, Jun 9, 2009 at 2:52 PM, ptrash wrote:
...
Hmm...it am not getting through it. I just want to generate a random
number and then compare it with other numbers. Something like
r = randomRIO (1, 10)
if (r > 5) then... else ...
You have to do it inside the IO monad, something like
myFunc  = do
        r <- randomRIO (1, 10
        if r > 5
            then ...
            else ...
/M
Or make the source of the pseudo-random numbers explicit:

import System.Random

function :: (RandomGen g, Random a) => g -> other args -> result
function gen whatever
    | r > 5     = blah newgen something
    | r < 3     = blub newgen somethingElse
    | otherwise = bling
      where
        (r,newgen) = randomR (lo,hi) gen

and finally, when the programme is run:

main = do
    args <- getArgs
    sg <- getStdGen
    foo <- thisNThat
    print $ function sg foo

If you're doing much with random generators, wrap it in a State monad.

Re: [Haskell-cafe] Convert IO Int to Int

Daniel Fischer