[Haskell-beginners] Type error in function binding

[Mats Rauhala]

On 15:50 Mon 02 Apr     , bahadýr altan wrote:
> Hi.
> I'm trying to write a code which counts the number of  'a's  in a string.
> it looks like this :
> 
> mycounter st =
> if st == [] then 0
> else if head st == 'a' then 1 + mycounter tail st else mycounter tail st
> 
> but it gives this error : 
> ERROR "deneme.hs":19 - Type error in function binding
> *** Term           :mycounter
> *** Type           : [Char] -> b
> *** Does not match : ([a] -> [a]) -> [Char] -> b
> *** Because        : unification would give infinite type
> 
> I have no idea about what I'm doing wrong. Can you help me with this please?

I didn't verify, but it could be that you need parenthesize the `counter tail st`
part.

A different kind of solution could be:

counter [] = 0
counter ('a':xs) = 1 + counter xs
counter (_:xs) = counter xs

Or maybe even: `length $ filter (== 'a') xs`

-- 
Mats Rauhala
MasseR
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