Re: [Haskell-cafe] [IO Int] -> IO [Int]

Daniel Fischer wrote:

On 5/4/07, Phlex wrote:

...

I'm trying to write a function with the signature [IO Int] -> IO [Int]

Control.Monad has a function (called "sequence") that does this for you. In fact, "sequence" is a more generic solution since its signature is ( Monad m => [m a] -> m [a]).

Unfortunately, this won't work for infinite lists either, for those you'd need an 'unsafe' action, namely 'unsafeInterleaveIO', like

import System.IO.Unsafe

conv :: [IO a] -> IO [a] conv [] = return [] conv (x:xs) = do a <- x as <- unsafeInterleaveIO (conv xs) return (a:as)

*Test> :set -fno-print-bind-result *Test> xs <- conv $ map return [1 .. ] *Test> take 20 xs [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]

HTH, Daniel

Thank you all for the very good answers. Sacha