调用方法的Sweet.js宏 [英] Sweet.js macro that calls a method

问题描述

我正在尝试编写一个sweet.js宏，该宏需要生成方法调用语法obj.method()，但是method作为字面量表达式传递给该宏.例如:

I'm trying to write a sweet.js macro which needs to generate method call syntax, obj.method(), but the method is passed in to the macro as a literal expression. For example:

mcall(obj, toString().length);
// becomes
obj.toString().length;

我有一些接近的东西:

macro mcall {
  rule { ($o, $m:expr) } => { $o.$m }
}

mcall(obj, toString().length);

但是，这显然扩展为:

obj . ( toString ( ) . length );

这些多余的括号是从哪里来的，我该如何去除它们?我应该使用案例规则和#{}吗?我尝试了这种排列，但是在没有额外括号的情况下仍然无法成功生成方法调用.

Where are these extra parentheses coming from, and how do I get rid of them? Should I be using case rules and #{}? I tried permutations of that but still couldn't succeed at generating a method call without extra parentheses.

推荐答案

因此，当前在sweet.js令牌中，绑定到:expr模式变量的令牌被包裹在括号中，以帮助获得优先权以使其正常工作.这是一种hack，很快就会得到修复(此处有更多讨论: https://github.com/mozilla/sweet.js/issues/314 ).

So currently in sweet.js tokens bound to an :expr pattern variable get wrapped in parens to help with getting precedence to work correctly. This is kind of a hack and will get fixed soon (some more discussion here: https://github.com/mozilla/sweet.js/issues/314).

您的示例的简单解决方案是不使用:expr，因为您实际上并不需要它:

The simple solution for your example is to just not use :expr since you don't really need it:

macro mcall {
  rule { ($o, $m ...) } => { $o.$m ... }
}

侧面说明:使用:expr在技术上是错误的，因为不允许.的RHS是不受限制的表达式(例如，2+4匹配$m:expr，但obj.2+4是语法错误).

Side note: using :expr is technically wrong here since the RHS of a . is not allowed to be an unrestricted expression (eg 2+4 matches $m:expr but obj.2+4 is a syntax error).

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