[Haskell-cafe] Where's the error in this snippet of code?

Christian Maeder maeder at tzi.de
Wed Mar 24 17:55:11 EST 2004

Alex Gontcharov wrote:
> Ignore the layout

pStack needs to be indented to the same level than digStack (or a 
"where" must be inserted after digStack).

> I can't find the error, running it gives parse error during compile on
> pStack, it is not very descriptive and I don't what is wrong.

after correct indentation, the error message of ghc is quite accurate:

     Couldn't match `[Integer]' against `Integer -> [Integer]'
	Expected type: [Integer]
	Inferred type: Integer -> [Integer]
     Probable cause: `pStack' is applied to too few arguments in the call
	(pStack xs)
     In the second argument of `(++)', namely `pStack xs'

> --Stack for the digits for numbers, a modulo b
>     digStack :: Integer->Integer->[Integer]
>     digStack a b
>       | a == 0 = []
>       | otherwise = (mod a b):(digStack (div a b) b)
>                      --Takes a list of remainders and
>                      pStack :: [Integer] -> Integer -> [Integer]
>                      pStack [] _ = []
>                      pStack (x:xs) a =
>                         digStack x a ++ pStack xs

the last expression should probably be "pStack xs a"

> I think I will never like Haskell :-)

Come on,

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