gistfile1

module Foo where

  groupBy :: forall a. (a -> a -> Boolean) -> [a] -> [[a]]
  groupBy _  []     =  []
  groupBy eq (x:xs) = case span (eq x) xs of
    {init = ys, rest = zs} -> (x:ys) : groupBy eq zs

  span :: forall a. (a -> Boolean) -> [a] -> { init :: [a], rest :: [a] }
  span p (x:xs') | p x = case span p xs' of {init = ys, rest = zs} -> {init: (x:ys), rest: zs}
  span _ xs            = {init: [], rest: xs}