I just watched this Mozilla video on some experimental work Tim Disney is doing for JS macros. While watching it, I also read came across Dave Herman's homoiconicity post.
Interesting stuff, and helped me to better understand how macros might fit into JavaScript, at least at a technical level.
My crude layman's explanation of macros: transpilers but only JS token
types are used, versus having to make your own whole grammar, and constrained to curlies
() {} [] as delimiters (thanks to Tim for the correction). These limitations are there in order to insert in a simplified
parser (called the reader) between the usual JS lexer and parser stages.
So macros seem to be useful when:
I am having trouble visualizing those use cases though. My initial reaction is that macros are something neat for a language enthusiast, but do not actually make coding, the sharing and reading of code, that much better, particularly since it involves a level of indirection that is subtle, the new grammar needs to be tracked down. I find this is the hardest part of understanding codebases, tracking down what different units of code are doing, where the definitions live.
My first impulse is to say, "just make a function" that does what you want, using existing JS grammar.
If a function is not enough, what you are probably wanting is a full custom language, so then a full grammar/transpiler makes sense. The use of transpilers are easier to call out in their use -- normally a different file extension, and by not being limited to JS token types/delimiters, you are more likely to create a terser grammar.
I can see the need to make transpiler construction easier. And if someone wanted to create a "like JS but with some tweaks", maybe create something higher level than something like jison to do that. I would have liked that when playing around with module syntax for JS, for example.
So it is hard for me to see the case for macros, at least as described in that video. They seem to be a middle ground between functions and full transpilers whose benefits seem to be outweighed by making it more difficult to comprehend code written in "JavaScript".
But I am trying to learn more about it. If anyone has pointers to the cases where macros shine and their use outweighs my perceived readability/code tracing costs, I would love to hear it. Feel free to leave a comment.
However, do not comment with at "yeah macros are dumb". This is an exploration in enlightenment. I'm already skeptical of macros, so I do not need that reinforcement. I'm looking for more concrete use cases, pros and cons on specific points, not fear of change.
Similarly, comments of the form "because, Language X has them and they are awesome" will likely not be informative. It is likely language X and JS do not share other properties and cultures that are in JS, like the propensity to create transpilers for JS. I want uses cases that for JS would not be solved via functions or a full transpiler.