module PreludeList where infixr 5 ++ infixl 9 !! infix 4 `elem`,`notElem` map f [] = [] map f (x:xs) = f x:map f xs []++ys = ys (x:xs)++ys = x:(xs++ys) concatMap f = concat . map f filter p [] = [] filter p (x:xs) = if p x then x:filter p xs else filter p xs concat = foldr (++) [] null [] = True null (_:_) = False head (x:_) = x tail (_:xs) = xs foldr f z [] = z foldr f z (x:xs) = f x (foldr f z xs) foldl f z [] = z foldl f z (x:xs) = foldl f (f z x) xs zip (x:xs) (y:ys) = (x,y):zip xs ys zip _ _ = [] unzip [] = ([],[]) unzip ((x,y):xys) = case unzip xys of (xs,ys) -> (x:xs,y:ys) length :: [a] -> Int length [] = 0 length (_:xs) = 1+length xs replicate n x = take n (repeat x) repeat x = xs where xs = x:xs take n xs = if n<=0 then [] else case xs of [] -> [] x:xs -> x:take (n-1) xs drop n xs = if n<=0 then xs else case xs of [] -> [] x:xs -> drop (n-1) xs all p xs = foldr ((&&).p) True xs any p xs = foldr ((||).p) False xs x `elem` xs = any (x==) xs x `notElem` xs = all (x/=) xs span p xs = (takeWhile p xs,dropWhile p xs) takeWhile p [] = [] takeWhile p (x:xs) = if p x then x:takeWhile p xs else [] dropWhile p [] = [] dropWhile p (x:xs) = if p x then dropWhile p xs else x:xs reverse xs = foldl (\ys y->y:ys) [] xs foldl1 f (x:xs) = foldl f x xs minimum xs = foldl1 min xs lookup :: Eq a => a -> [(a,b)] -> Maybe b lookup x [] = Nothing lookup x ((x',y):xys) = if x'==x then Just y else lookup x xys (!!) :: [a] -> Int -> a xs !! n = if n<0 then error "Prelude.!!: negative index" else case xs of [] -> error "Prelude.!!: index too large" x:xs -> if n==0 then x else xs!!(n-1) {- lines :: String -> [String] lines "" = [] lines s = let (l, s') = break (== '\n') s in l : case s' of [] -> [] (_:s'') -> lines s'' -} unlines :: [String] -> String unlines = concatMap (++ "\n")