在haskell中具有多值函数的功能组合? [英] Functional composition with multi-valued functions in haskell?

问题描述

我想知道是否可以使用带有多个参数的函数进行函数组合.我希望能够做这样的事情

I was wondering if it was possible to do functional composition with functions that take more than one argument. I want to be able to do something like this

x = (+3).(*)

设置 x 等于一个函数，将两个数字的乘积加三.

setting x equal to a function that adds three to the product of two numbers.

推荐答案

有多种方法可以做到，但都有些别扭.

There are multiple ways to do it, but they're all somewhat awkward.

((+3).) . (*)
≡ fmap (+3) . (*)
≡ curry $ (+3) . uncurry (*)
≡ l r -> l*r + 3

哦，等等，这是签名，还有一个紧凑的定义，猜猜它叫什么...

Oh, wait, this was the signature where there's also a compact definition, guess what it's called...

((.).(.)) (+3) (*)

我认为最明确的 lambda 解决方案在这里是最好的.

I'd argue that the lambda solution, being most explicit, is rather the best here.

什么有帮助，通常只是作为一个(或两个)行在本地完成，是将此组合定义为自定义中缀:

What helps, and is often done just locally as a one(or two)-liner, is to define this composition as a custom infix:

(.:) :: (c->d) -> (a->b->c) -> a->b->d
f .: i = l r -> f $ i l r

它允许您简单地编写 (+3) .: (*).

Which allows you to write simply (+3) .: (*).

顺便说一句，对于类似的(b->b->c) ->(a->b)->a->a->c(为中缀的两个参数预先组合正确的函数)存在广泛使用的标准实现.

BTW, for the similar (b->b->c) -> (a->b) -> a->a->c (precompose the right function to both arguments of the infix) there exists a widely-used standard implementation.

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