[Haskell-cafe] Occurs check error, help!

[Yuras Shumovich]

2010/3/20 boblettoj <boblettoj99 at msn.com>:
>
> Ah yes, that makes sense now, however i have another problem, here is the
> updated code:
>
> --function used to shuffle cards
> --list equals random member of array plus the rest of the array
> --i is randomly generated from range of length equal to that of cards.
> shuffle :: Int -> [a] -> [a]
> shuffle i [] = []
> shuffle i cards = [(cards!!i) :
>        (shuffle (randomR(0, ((length cards)-2)))
>        (delete (cards!!i) cards))]
>
> and the message:
> cards.hs:32:11:
>    Couldn't match expected type `Int'
>           against inferred type `g -> (Int, g)'
>    In the first argument of `shuffle', namely
>        `(randomR (0, ((length cards) - 2)))'
>    In the second argument of `(:)', namely
>        `(shuffle
>            (randomR (0, ((length cards) - 2))) (delete (cards !! i)
> cards))'
>    In the expression:
>          (cards !! i)
>        : (shuffle
>             (randomR (0, ((length cards) - 2))) (delete (cards !! i)
> cards))
>
> Doesn't RandomR return an Int?

No, see docs
http://haskell.org/hoogle/?hoogle=randomR

> thanks
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