takeWhile and dropWhile

[srid]

I was somewhat surprised that these functions were missing from the standard library (I needed them to implement groupBy). Any reason these functions (with better implementation than mine) cannot be added to the standard library?

-- Take a sorted list and group it by some key function
groupBy : (List a) -> (a -> String) -> (List (String, (List a)))
groupBy list f =
  case list of
    []       -> []
    hd::tl   -> let
                  key = f hd
                  chunk = takeWhile (\x -> (f x) == key) tl
                  rest = dropWhile (\x -> (f x) == key) tl
                in
                  (key, hd :: chunk) :: groupBy rest f

takeWhile : (a -> Bool) -> (List a) -> (List a)
takeWhile predicate list =
  case list of
    []       -> []
    hd::tl   -> if | (predicate hd) -> hd :: takeWhile predicate tl
                   | otherwise -> []

dropWhile : (a -> Bool) -> (List a) -> (List a)
dropWhile predicate list =
  case list of
    []       -> []
    hd::tl   -> if | (predicate hd) -> dropWhile predicate tl
                   | otherwise -> tl

[srid]

Oops, apologies of being lazy and not having read the contribution guidelines.

[srid]

Oops, apologies of being lazy and not having read the contribution guidelines.