+1和-1之间的差异 [英] The difference between +1 and -1

问题描述

 > ：t（+1）
（+1）:: Num a => a  - > a 
 
> ：t（-1）
（-1）:: Num a => a 
  

第二个函数不是函数吗？我必须写（+（ - 1））或者有更好的方法吗？

解决方案

这是因为（ - 1）被解释为负数，但是（+ 1）被解释为curried函数（\ x-> 1 + x）。

在haskell中， （a **）是（**）a 和的语法糖（* * a）是（\ x - > x ** a）。然而，（ - ）是一种特殊情况，因为它既是一元运算符（否定）又是二元运算符（减号）。因此，这种语法糖在这里不能被明确地应用。当你想（\ x - > a-x）时，你可以写（ - ）a 正如已经在柯里化减法中回答的那样，您可以使用函数 negate 和减去以区分一元和二元 - 函数。

> :t (+1)
(+1) :: Num a => a -> a

> :t (-1)
(-1) :: Num a => a

How come the second one is not a function? Do I have to write (+(-1)) or is there a better way?

解决方案

This is because (-1) is interpreted as negative one, however (+1) is interpreted as the curried function (\x->1+x).

In haskell, (a **) is syntactic sugar for (**) a, and (** a) is (\x -> x ** a). However (-) is a special case since it is both a unary operator (negate) and a binary operator (minus). Therefore this syntactic sugar cannot be applied unambiguously here. When you want (\x -> a - x) you can write (-) a, and, as already answered in Currying subtraction, you can use the functions negate and subtract to disambiguate between the unary and binary - functions.

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