[Haskell-cafe] Re: filterFirst

[apfelmus]

Alexteslin wrote:
> filterAlpha :: (a -> Bool) -> [a] -> [a]
> filterAlpha f [] = []
> filterAlpha f (x:xs)
> 	|f x 	= x : filterAlpha xs
> 	|otherwise	= filterAlpha xs
> 
> 
> and i am getting this error message:
> 
> Type error in application
> Expression :filterAlpha xs
> Type        : [b]
> Dous not match : a -> Bool

  filterAlpha :: (a -> Bool) -> [a] -> [a]
  filterAlpha f [] = []
  filterAlpha f (x:xs)
     | f x       = x : filterAlpha f xs
     | otherwise =     filterAlpha f xs

filterAlpha  has two parameters. The first parameter is a function (a ->
Bool), the second is a list [a]. The error message complains that  xs ,
which you actidentially gave as first parameter, is a list [a] and not a
function (a -> Bool).

Regards,
apfelmus