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Macros are a menace (mit.edu)
6 points by palsecam 3566 days ago | 4 comments


3 points by palsecam 3566 days ago | link

Very interesting points about macros drawbacks.

pg is a well-known advocate of macros, and I suppose he influenced a lot of people in this opinion. I do like macros, but it's true, too many times you're doing it wrong if you're defining a macro.

Richard Gabriel (author of Worse is better, Lucid founder, etc.: in short: Lisp expert) said:

   "Macros encourage people who are not good at
   language design to do something equivalent to language design,
   using tools that don't help, and with effects that are too
   powerful. This makes code unreadable to people joining later and
   for the authors after time has passed. Well designed macros are
   well documented, but this doesn't happen much."
Think about it.

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2 points by akkartik 3566 days ago | link

Interesting. I suspect I overuse macros; I try consciously to improve by constraining the surface area of the program that lies under defmacro, but there's a long way to go.

One pattern: I often used to use defmacro just to get call-by-reference. Most of the time I can get by with just primitives.

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1 point by conanite 3566 days ago | link

He makes some interesting points, but macros are like everything else that's useful (fire, nuclear power ...), they can be abused. It's fair to warn people about macros, just as people are warned repeatedly about multi-threading; but it doesn't mean macros, or multi-threading, are wrong or bad. Having a few years of practicing "Don't Repeat Yourself" in java, perhaps, you have finally hit the limit, and realise that removing more duplication means a net increase in volume of code. Arc and assembly are the only non-condescending languages I know, and I love the freedom of writing unfettered code in arc.

I notice that arc's macros are mostly very short and to the point, and are strictly hygienic even though the core language doesn't impose it. As for me, I'm still learning this discipline, just as it took me a while to understand why short methods and small classes are "better".

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3 points by idoh 3564 days ago | link

I've found them really useful to build up html. Compare "tag" as a macro versus "tag" as a function.

  (tag body
    (tag div
      (map display-thread threads)))

  (tag body
    `(tag div
       ,@(map display-thread threads)))
This is sort of a simplistic example, but once you get deep into it, you are always quoting and unquoting, and it just gets too tedious.

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