[英]Transforming a Haskell function to a point free representaion
I want to create a pointfree function that takes a list of functions, applies a single argument to each listed function, and then compresses the list via another function. 我想创建一个无点函数,该函数采用函数列表,将单个参数应用于列出的每个函数,然后通过另一个函数压缩列表。 A pointfree version of this function would have the following type signature: 该函数的无点版本将具有以下类型签名:
multiplex :: ([a] -> b) -> [(c -> a)] -> (c -> b)
And an example usage: 以及示例用法:
invariantsHold :: (Integral a) => a -> Bool
invariantsHold = multiplex (all id) [(>=0),(<=50),even]
I was able to write the following: 我能够编写以下内容:
multiplex :: ([a] -> b) -> [(c -> a)] -> c -> b
multiplex f xs e = f $ map ((flip ($)) e) xs
This implementation is not pointfree, how can I transform this function to a pointfree representation? 此实现不是无点的, 如何将这个函数转换为无点的表示形式?
Not in pointfree style, but surely could be simplified significantly by using Applicative
(need to import Control.Applicative
): 并非采用无点样式,但可以肯定地通过使用Applicative
进行简化(需要导入Control.Applicative
):
multiplex f xs e = f $ xs <*> pure e
invariantsHold
also could be simplified a little: invariantsHold
也可以稍微简化一下:
invariantsHold = multiplex and [(>=0),(<=50),even]
Using sequenceA
(from Data.Traversable
) is another way to define this multiplex
: 使用sequenceA
(来自Data.Traversable
)是定义此multiplex
另一种方法:
multiplex f xs e = f $ sequenceA xs e
And this definition can be rewritten in pointfree style (give by pointfree
): 这个定义可以用pointfree样式重写(由pointfree
):
multiplex = (. sequenceA) . (.)
or 要么
multiplex = flip ((.) . (.)) sequenceA
Beautiful, but seems pointless to me :-) 漂亮,但对我来说似乎毫无意义:-)
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