使用模式匹配或函数组合实现revmap函数

Question

高阶函数映射定义：

map :: (a -> b) -> [a] -> [b]
map f [] = []
map f (x:xs) = f x:map f xs

那么如何用模式匹配/使用函数组合来编写revmap函数？

Answer 1

假设您想要类似OCaml的rev_map功能：

revmap :: (a -> b) -> [a] -> [b]
revmap f xs = go xs []
  where
    go [] acc     = acc
    go (x:xs) acc = go xs (f x : acc)