Re: Ellipsis in the _pattern_ Taylor Campbell 12 Oct 2003 13:54 UTC

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
SYNTAX-RULES macros with SYNTAX-RULES macros (e.g., to implement

>                                                         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
Andre van Tonder's monadic CPS macros!)  You'll learn quite a lot of
by doing so, and also several pitfalls of SYNTAX-RULES.

> 				Bear