連続するスペースの削除いろいろ

main.hs

import Data.List (group)


removeSequencialSpace1 :: String -> String
removeSequencialSpace1 = concat . compressSpaces . group
    where
        compressSpaces :: [String] -> [String]
        compressSpaces = foldr (\str acc -> (if ' ' `elem` str then " " else str): acc) []


removeSequencialSpace2 :: String -> String
removeSequencialSpace2 src = loop src False
    where
        loop :: String -> Bool -> String
        loop []       _    = []
        loop (' ':xs) True =    loop xs True
        loop (  x:xs) _    = x: loop xs (x == ' ')
        
  
removeSequencialSpace3 :: String -> String
removeSequencialSpace3 = foldr loop ""
    where
        loop :: Char -> String -> String
        loop x   ""          = [x]
        loop ' ' acc@(' ':_) = acc
        loop x   acc         = x: acc
        
        
removeSequencialSpace4 :: String -> String
removeSequencialSpace4 (' ':' ':ys) =    removeSequencialSpace4 (' ':ys)
removeSequencialSpace4 (  x:  y:ys) = x: removeSequencialSpace4 (  y:ys)
removeSequencialSpace4 ys           = ys

main :: IO()
main = interact removeSequencialSpace4