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1 point by icemaze 4008 days ago | link | parent

1. Yes, that's much nicer, thanks.

2. "the problem is how easy it is to write something incorrect". Very true.

"evaluation order has nothing to do with macros" I'm sorry but that's incorrect. An example will show you why:

  (mac sum (x y) `(+ ,y ,x)) ; This is a toy, but some macros suffer from the same problem without being so trivial/stupid
  (= x 1)
  (+ x (++ x))   ; -> 3, the expected result
  (= x 1)
  (sum x (++ x)) ; -> 4, wrong result
Common Lisp macros usually solve this with a meta-macro called once-only that forces things to be evaluated in the right order and only once. Google it for more info.

"lisp-2 is statistically better". Well, not if people know that shadowing function can cause problems. Now a question arises: does shadowing functions solve problems in a way not possible with other methods? Does shadowing function make programs shorter? Or, equivalently, is shadowing functions really that useful? (Please provide examples if you answer this). If not, using a lisp-2 and being careful is enough. But yes, it's easy to overlook a symbol and make a mistake that can be costly. On that, I agree.

3. You are right and that's why I said "I'm not sure about [a lisp-1 like] Arc".

4. That seems really interesting, I'll look into it.



1 point by elibarzilay 4008 days ago | link

You didn't understand me.

One of the things that you can do with macros is specify evaluation order, that's correct. You should also know when and how to evaluate your arguments, as done with the once-only utility (which is really just a thin wrapper around the obvious solution of binders).

But when I said "evaluation order has nothing to do with macros" I meant the kind of macro facility that you use (the original context of this thread was hygiene). No matter which kind of macros you have, the above issues are still the same.

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