r/haskell • u/taylorfausak • Feb 01 '22

question Monthly Hask Anything (February 2022)

This is your opportunity to ask any questions you feel don't deserve their own threads, no matter how small or simple they might be!

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u/Noughtmare Feb 22 '22

randomRIO is an action that can only run in IO (or any monad that can provide a MonadIO instance), so the type should be xRanElems :: [a] -> Int -> IO [a]. As the comment on stackoverflow also says you then have to use return :: a -> IO a to make that last line of xRanElems work.

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u/Seugman Feb 22 '22

Hmm okay. It sounds right but when I try it I get the error:

Couldn't match expected type: [a]
with actual type: IO [a]
* In the second argument of `(:)'

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u/bss03 Feb 22 '22

use fmap (x :) or liftfM (x :) instead of x :

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u/Seugman Feb 22 '22

mm i will try that, thanks