[Haskell-cafe] Re: filterFirst

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