[Haskell-cafe] Re: Occurs check error, help!

adamtheturtle kill2thrill at hotmail.com
Sun Mar 21 23:31:12 EDT 2010

So I have the code 

shuffle :: Int -> [a] -> [a]
shuffle i [] = []
shuffle i cards = (cards!!i) : shuffle (fst pair) (delete (cards!!i) cards)
    where pair = randomR (0, 51) (mkStdGen 42)

and it doesn't work, am I missing something?

    Could not deduce (Eq a) from the context ()
      arising from a use of `delete' at Cards.hs:39:51-73
    Possible fix:
      add (Eq a) to the context of the type signature for `shuffle'
    In the second argument of `shuffle', namely
        `(delete (cards !! i) cards)'
    In the second argument of `(:)', namely
        `shuffle (fst pair) (delete (cards !! i) cards)'
    In the expression:
          (cards !! i) : shuffle (fst pair) (delete (cards !! i) cards)
Failed, modules loaded: none.

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