2007-01-16 filter関数。 Haskell filter :: (a -> Bool) -> [a] -> [a] 第2引数[a]の要素で(a -> Bool)がTrueの要素のみ集めてリストで返す。 main = print $ filter filterTest ["abc", "de", "f", "gh"] filterTest :: String -> Bool filterTest cs = if length cs == 2 then True else False 結果。 ["de","gh"]