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

[Ivan Miljenovic]

On 22 March 2010 13:49, adamtheturtle <kill2thrill at hotmail.com> wrote:
> Just tried 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 I get:
>
> Could not deduce (Eq a) from the context ()
>      arising from a use of `delete' at Cards.hs:(23,51)-(24,8)
>    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.
>
>
> Any ideas?

Yes: do what it says!

Hint: http://hackage.haskell.org/package/random-shuffle


-- 
Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com
IvanMiljenovic.wordpress.com