haskell - 将 `apply` 映射到函数列表

Question

Learn You a Haskell演示使用柯里化(Currying)的映射:

*Main> let xs = map (*) [1..3]

xs 现在等于 [(1*), (2*), (3*)]

已编辑以根据 Antal S-Z 更正订单的评论。

我们可以获取列表中的第一项，并对其应用 3 - 返回 3*1。

*Main> (xs !! 0) 3
3

但是，我如何应用下面的 foo 将 1 应用于 xs 中的所有柯里化(Currying)函数？

*Main> let foo = 1
*Main> map foo xs

<interactive>:160:5:
    Couldn't match expected type `(Integer -> Integer) -> b0'
                with actual type `Integer'
    In the first argument of `map', namely `foo'
    In the expression: map foo xs
    In an equation for `it': it = map foo xs

期望的输出:

[1, 2, 3]

Answer 1

使用($)函数...

Prelude> :t ($)
($) :: (a -> b) -> a -> b

...只将第二个参数传递给它。

Prelude> let foo = 2
Prelude> map ($ foo) [(1*), (2*), (3*)]
[2,4,6]