> My question is: Do the ... in the case > > ((test id _kt _kf) _kt) ... > > produce one case for each identifier in the list?
Yes, they do.
> I am guessing that this is what they do. However, they are mentioned as
> literals in the inner syntax-rules,
No, they aren't. The (id ...) form is expanded by the outer syntax-rules
form, as part of expanding the id-memv?? macro. They don't remain in the
expanded result. For example, if you call
(id-memv?? foo (foo bar baz) kt kf)
the expansion will look like
(let-syntax ((test
(syntax-rules (foo bar baz)
((test foo _kt _kf) _kf)
((test bar _kt _kf) _kf)
((test baz _kt _kf) _kf)
((test otherwise _kt _kf) _kf))))
(test foo kt kf))
> so I was thinking the expansion will simply put literally three dots there,
> instead of understanding the three dots to mean "for each of the ids".
>
> And also I still am unsure about whether the three dots work like this at all.
They do.
> When one puts the ... after a compound expression, that contains the thing,
> that
> the ... were after in the matching -- in this case they were after id, and id
> is
> contained in the compound expression (test id _kt _kf) _kt) -- does that make
> the compound expression be generated for each thing matched?
Yes, see:
(syntax->datum
(with-syntax ((simple #'a)
((compound ...) #'(b c d))
(((nested-compound ...) ...) #'((e f g) (h i j))))
#'(((simple compound nested-compound) ...) ...)))
⇒ (((a b e) (a c f) (a d g)) ((a b h) (a c i) (a d j)))
> But if this is the case, then I might be misunderstanding the Guile docs at
> https://www.gnu.org/software/guile/manual/html_node/Syntax-Rules.html:
>
> "Instances of a pattern variable in the template must be followed by an
> ellipsis."
Note that this is talking about the patterns, not the syntax forms. But it
is slightly misleading: also in patterns it is perfectly possible to do
something like
(syntax->datum
(with-syntax ((((a b) ...) #'((1 2) (3 4) (5 6))))
#'((a ...) . (b ...))))
⇒ ((1 3 5) 2 4 6)
Note the pattern
((a b) ...)
An ellipsized pattern is recognized by the ellipsis, but it doesn't
need to follow a simple pattern variable, it can follow a nested
pattern.
Best,
Jean
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