Map是具有两个参数的函数吗? [英] Is Map a function with Two Arguments?

问题描述

我正在尝试解决一个选择题，指出以下内容

I'm trying to solve a multiple choice question that states the following

• 地图是一个重载函数
• map是一个多态函数
• 地图是咖喱函数
• 地图是高阶函数
• map是具有两个参数的函数

我知道地图过载，多态，咖喱和高阶.这是否意味着map是仅具有单个参数的函数?(我意识到这是函数被咖喱化的结果，并且haskell仅具有带单参数的函数，并通过currying和partial application来应用多个参数函数)

I know that map is overloaded, polymorphic, curried and higher-order. Does that mean that map is a function with just a single argument ? (I realize that this is a consequence of a function being curried, and haskell only has functions with single arguments with multiple argument functions being applied through currying and partial application)

推理正确吗?如果是这样，则map函数如何通过部分应用程序评估函数?

Is the reasoning correct ? And if so, how does the map function evaluate a function through partial application ?

推荐答案

与所有Haskell函数一样， map 是单参数函数.让我们看一下它的类型签名:

Like all Haskell functions, map is a single-argument function. Let's have a look at its type signature:

map :: (a -> b) -> [a] -> [b]

等效于:

map :: (a -> b) -> ([a] -> [b])

我认为这种签名在您的情况下更容易理解: map 获得一个参数-从 a 到 b 的函数-并返回另一个功能，这次是从 [a] 到 [b] .

I think this signature is easier to understand in your case: map gets one argument - a function from a to b - and returns another function, this time from [a] to [b].

本质， map 提升"一个功能-它需要一个常规功能并提升"它，以便它可以在列表上使用.提升的想法出现在Haskell的多个地方.

Essentialy, map "lifts" a function - it takes a regular function and "lifts" it so it'll work on lists. This idea of lifting appears in several places in Haskell.

例如， even 是从 Int 到 Bool 的函数-它需要一个数字并在为偶数时返回true.而且 map even 是从 [Int] 到 [Bool] 的函数-它接受一个数字列表并返回一个布尔值列表. map even 只是 even 在不同的上下文"中工作-列表而不是单个值.

For example, even is a function from Int to Bool - it takes a number and returns true iff it is even. And map even is a function from [Int] to [Bool] - it takes a list of numbers and returns a list of boolean values. map even is just even working in a different "context" - lists instead of single values.

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