+1 和 -1 之间的区别
> :t (+1)
(+1) :: Num a => a -> a
> :t (-1)
(-1) :: Num a => a
为什么第二个不是函数？我必须写 (+(-1)) 还是有更好的方法？
> :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?
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这是因为
(-1)被解释为负数，而(+1)被解释为柯里化函数(\x->1+x ）。在 haskell 中，
(a **)是(**) a的语法糖，而(** 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，这个语法糖不能明确地应用在这里。当您想要(\x -> a - x)时，您可以编写(-) a，并且，正如 柯里化减法，您可以使用函数negate和subtract来消除一元和二进制之间的歧义-函数。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 functionsnegateandsubtractto disambiguate between the unary and binary-functions.我刚刚找到了一个名为
subtract的函数，所以我也可以说subtract 1。我发现这很有可读性:-)I just found a function called
subtract, so I can also saysubtract 1. I find that quite readable :-)正如其他人所指出的，
(-1)是负数。减一函数是\x -> x-1、翻转 (-) 1或实际上(+ (-1))。-在 表达式语法。+不是，大概是因为正文字不需要前导加号，允许它会导致更多混乱。编辑：我第一次弄错了。
((-) 1)是函数“减一”，或(\x -> 1-x)。(-1)is negative one, as others have noted. The subtract one function is\x -> x-1,flip (-) 1or indeed(+ (-1)).-is treated as a special case in the expression grammar.+is not, presumably because positive literals don't need the leading plus and allowing it would lead to even more confusion.Edit: I got it wrong the first time.
((-) 1)is the function "subtract from one", or(\x -> 1-x).