apelsin-1.2: src/List2.hs

module List2 (stripw, intmean, replace, mread, split, breakDrop) where
import Prelude hiding (foldr, foldl, foldr1, foldl1)
import Data.Char
import Data.Foldable

stripw :: String -> String
stripw = dropWhileRev isSpace . dropWhile isSpace

dropWhileRev :: (a -> Bool) -> [a] -> [a]
dropWhileRev p = foldr (\x xs -> if p x && null xs then [] else x:xs) []

intmean :: (Integral i, Foldable f) => f i -> i
intmean l = if len == 0 then 0 else lsum `quot` len where
	(len, lsum) = foldl' (\(!n, !s) elm -> (n+1, s+elm)) (0, 0) l

replace :: (a -> Bool) -> a -> [a] -> [a]
replace f y (x:xs)
	| f x		= y : xs
	| otherwise	= x : replace f y xs
replace _ _ []		= []

mread :: (Read a) => String -> Maybe a
mread x = case reads x of
	[(a, _)]	-> Just a
	_		-> Nothing

split :: Eq a => a -> [a] -> [[a]]
split _ [] = []
split d s  = case break (== d) s of
	(w, s') -> w : case s' of
		[_]   -> [[]]
		_:s'' -> split d s''

		[]    -> []

breakDrop :: (a -> Bool) -> [a] -> ([a], [a])
breakDrop f xs = let (a, b) = break f xs
	in (a, dropWhile f b)