[Haskell-beginners] Need Help

[kaushal Pathak]

Whats the issue with following pgm to find permutation of a string

permute myStr = foldl(\acc x1 ->
                      (foldr(\x2 acc1 ->
                                 (zipWith (\x3 y3 -> x3 ++ [x1] ++ y3)
(inits acc1) (tails acc1)))
                       [] acc))
                    [] myStr


On Wed, Apr 29, 2009 at 6:35 PM, kaushal Pathak <kaushalkp at gmail.com> wrote:

> Here is another one liner I am stuck at(Find permuation of string), here is
> my one line code :
>
> permute myStr = foldr(\x acc -> (zipWith (\x1 y1 -> x1 ++ [x] ++ y1) (inits
> acc) (tails acc))) [] myStr
>
> and here is 5 line error ;-(
>
>     Occurs check: cannot construct the infinite type: a = [a]
>       Expected type: [a]
>       Inferred type: [[a]]
>     In the expression:
>         (zipWith (\ x1 y1 -> x1 ++ x ++ y1) (inits acc) (tails acc))
>     In the first argument of `foldr', namely
>         `(\ x acc
>               -> (zipWith (\ x1 y1 -> x1 ++ x ++ y1) (inits acc) (tails
> acc)))'
>
>
> Will really appreciate your help in moving ahead
>
> Regards
> Kaushal
>
>
>
>
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