在ReasonML中，在最后一个管道之后使用快速管道运算符编译错误 [英] Compile error using fast pipe operator after pipe last in ReasonML

问题描述

在很多 地方表示它们是彼此的直接替代。是否要将值作为最后一个参数发送给函数？最后使用管道（ |> ）。要将其作为第一个参数发送？使用快速管道（曾经在 |。上使用，现在已弃用了-> ）。

The way that the "fast pipe" operator is compared to the "pipe last" in many places implies that they are drop-in replacements for each other. Want to send a value in as the last parameter to a function? Use pipe last (|>). Want to send it as the first parameter? Use fast pipe (once upon a time |., now deprecated in favour of ->).

因此，就像我直到今天早些时候所做的那样，您的思考将被宽恕，以下代码将使您获得正则表达式匹配项之外的第一个匹配项：

So you'd be forgiven for thinking, as I did until earlier today, that the following code would get you the first match out of the regular expression match:

Js.String.match([%re "/(\\w+:)*(\\w+)/i"], "int:id")
|> Belt.Option.getExn
-> Array.get(1)

但是您会错的（再次，就像我今天早些时候一样。 ..）

But you'd be wrong (again, as I was earlier today...)

相反，编译器发出以下警告：

Instead, the compiler emits the following warning:

We've found a bug for you!
OCaml preview 3:10-27
This has type:
  'a option -> 'a
But somewhere wanted:
  'b array

请参见

See this sandbox. What gives?

推荐答案

看起来像是搞砸了-> ，因此它实际上被解释为

Looks like they screwed up the precedence of -> so that it's actually interpreted as

Js.String.match([%re "/(\\w+:)*(\\w+)/i"], "int:id")
|> (Belt.Option.getExn->Array.get(1));

内联运算符：

Array.get(Belt.Option.getExn, 1, Js.String.match([%re "/(\\w+:)*(\\w+)/i"], "int:id"));

或部分应用程序更明确，因为Reason的语法在计算时有些混乱：

or with the partial application more explicit, since Reason's syntax is a bit confusing with regards to currying:

let f = Array.get(Belt.Option.getExn, 1);
f(Js.String.match([%re "/(\\w+:)*(\\w+)/i"], "int:id"));

用<$ c替换-> $ c> |。有效。与将 |> 替换为 |。一样。

Replacing -> with |. works. As does replacing the |> with |..

我认为这是Reason中的错误，但是无论如何都建议不要使用快速管道，因为它会带来很多混乱，而带来的好处却很小。

I'd consider this a bug in Reason, but would in any case advise against using "fast pipe" at all since it invites a lot of confusion for very little benefit.

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