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1 point by absz 5955 days ago | link | parent

Speaking of "real gensyms," is there a reason uniq isn't simply defined (in ac.scm) to be

  (xdef 'uniq gensym)
? mzscheme's gensym has all the right properties:

  > (gensym)
  g26
  > (define g (gensym))
  > g
  g27
  > (equal? g 'g27)
  #f
  > (gensym 'prefix)
  prefix28
  > (gensym "string")
  string29
Does something break because they aren't "real" symbols? Or can we just (on Anarki) go ahead and make this change?


2 points by conanite 5955 days ago | link

speaking of gensyms, is there a reason uniq isn't defined in arc? one less axiom? (on a related note, I don't know why sig is defined in ac.scm, it doesn't seem to be otherwise referenced there)

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1 point by absz 5954 days ago | link

Because if/when we have real gensyms, where if we have

  arc> (= gs (uniq))
  gs2003
then (is gs 'gs2003) returns nil, instead of t (which it currently does), we won't be able to define uniq in Arc. It's another datatype (the "uninterned symbol"), and thus it needs an axiom. The axiom could be something besides uniq (string->uninterned-symbol, for instance, or usym) if (isnt (usym "foo") (usym "foo")).

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1 point by conanite 5954 days ago | link

Aha. So uniq in its current form is really 'kinda-uniq. How important is it that gensyms aren't equal to each other? I mean, if "everyone knows" /gs[0-9]+/ is "reserved" for gensyms, then all we need do is not make symbols matching that pattern. Thus is the language minimaler.

I'm just being lazy. It can't be that difficult to implement ...

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2 points by absz 5954 days ago | link

For now, it's not: see http://arclanguage.org/item?id=7529 . Thanks to mzscheme, it's a one-line change :)

And does that really make the language more minimal? If we leave uniq as it is, we could move it to arc.arc, but we have the axiom that symbols of the form /gs\d+/ are forbidden; if we change uniq, uniq is an axiom, but we don't have to worry about formats.

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2 points by stefano 5954 days ago | link

Even if Arc were not based on mzscheme the change would be minimal: it takes exactly the same operations as creating a normal symbol, with the difference that it doesn't have to be interned.

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2 points by conanite 5953 days ago | link

"doesn't have to be", or must not be interned? I'm thinking the latter, if the point is to guarantee that no other symbol shall be equal to a gensym ...

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3 points by stefano 5953 days ago | link

You're right: it must not be interned.

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2 points by almkglor 5955 days ago | link

I don't think anything would break; care to try?

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1 point by absz 5954 days ago | link

Alright, done and on the git.

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