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Re: Ellipsis in the _pattern_




On Sunday, Oct 12, 2003, at 00:42 US/Eastern, bear wrote:

You know, if it doesn't make sense to you it probably means the thing I'm thinking about is a nonissue anyway. As I said, I haven't eaten and breathed enough macrology to fully understand the intent of ::: in the first place.
I just have the impression that if we actually need it,

Well, we might not. I'm not sure, but it seems useful to me when processing SYNTAX-RULES macros with SYNTAX-RULES macros (e.g., to implement SYNTAX-RULES).

then something might break down if we want to go to meta-macros or meta-meta macros and don't have a corresponding "nested" form or the ability to produce/match it in
the inputs to our higher-order macros.

Perhaps it would be good if I specify further: ::: in the template literally generates the identifier ':::', because there's nothing special it would do, until the macro gets expanded into another macro whose pattern contains :::.

Still, the reason I doubt its actual utility is that I don't think anything prevents ... from matching a "sequence" of length one whose only member is
another ellipsis.

Yes, ... might match a sequence containing ellipsis, but still I want to be able to literally match ellipsis: I want to be _sure_ of the fact that what I
am matching is ellipsis.

Maybe I should get embarassed about my ignorance here and shut up.

Better yet, write some amazingly complex CPS macros. (No cheating by using Andre van Tonder's monadic CPS macros!) You'll learn quite a lot of macrology
by doing so, and also several pitfalls of SYNTAX-RULES.

				Bear