リスト内包表記でmapとfilter
map(写像)は、再帰で書くとこう
mapp _ [] = [] mapp f (x: xs) = f x : mapp f xs
リスト内包表記を使った場合はこうなる
map f xs = [f x | x <- xs]
filter(濾過)は再帰で書くとこう
filter _ [] = [] filter p (x:xs) = if (f x) then (x:(filter p xs)) else (filter p xs)
リスト内包表記を使った場合はこうなる
filter p xs = [x | x <- xs, p x]