F# 中的加法类型 (+) [英] Type of addition (+) in F#

问题描述

我刚刚了解到 OCAML 必须有一个 . 后缀来进行浮点运算.一个例子是 3.+.4. 等于 7.(浮点数).但是，F# 以相同的方式处理浮点数和整数运算，因此 3 + 4 (int) 和 3.+ 4.(浮动)有效.

I just learned that OCAML have to have a . postfix for doing float arithmetic. An example would be 3. +. 4. which equals 7. (float). However, F# handles float and integer arithmetic in the same way, so both 3 + 4 (int) and 3. + 4. (float) works.

F# 有 + 自然分配给 int 所以 let add a b = a + b 是 int ->内部 ->整数.事实上 (+) 给了我 val it : (int -> int -> int) = <fun:it@6-1>.

F# have + naturally assigned to int so let add a b = a + b is of type int -> int -> int. And indeed (+) gives me val it : (int -> int -> int) = <fun:it@6-1>.

这导致了我认为非常违反直觉的以下序列:

That leads to the following sequence which I think quite counter-intuitive:

> 3. + 4.;;
val it : float = 7.0
> (+);;
val it : (int -> int -> int) = <fun:it@8-2>

所以我的问题是:重载"是由编译器中的特殊机制/案例完成的，还是语言范围内的事情，所以我可能可以定义一个名为 add 的函数(或其他任何东西)对整数有一个定义，对浮点数(或任何其他类型)有一个定义.

So my question is: Is the "overloading" done by a special mechanism/case in the compiler or is this a language-wide thing so I potentially can define a function called add (or anything else) which have a one definition for integers and one for floats (or any other type.)

推荐答案

简而言之，F# 具有通过 inline 关键字和静态成员约束"的临时重载机制.内置数学运算符还有一些特殊的魔法，它神奇地假设 int 类型没有其他约束.(+) 几乎是所有 F# 中最特别/最神奇的东西，因此它不能很好地介绍语言/类型系统.

Briefly, F# has an ad-hoc-overloading mechanism via the inline keyword and "static member constraints". There is some further magic specific to the built-in math operators, which magically assumes type int the absence of other constraints. (+) is just about the most special/magical thing in all of F#, so it does not make for a nice introduction to the language/type system.

一般来说，重载"对于静态类型、类型推断的语言来说是困难的.F#在这里的选择非常务实.OCaml 做了不同的、简单的、务实的事情(没有重载).Haskell 做了一个不同的、复杂但优雅的事情(类型类).它们在语言/库设计空间中都有些合理.

In general, "overloading" is difficult for statically-typed, type-inferred languages. F#'s choices here are very pragmatic. OCaml does a different, simple, pragmatic thing (no overloading). Haskell does a different, complex-but-elegant thing (type classes). They're all somewhat reasonable points in the language/library design space.

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