BTW, for future readers... in this example:
(define-syntax if*
(syntax-rules (then else)
((_ ?test (then ?consequent) (else ?alternate))
(if ?test ?consequent ?alternate))))
The "?" part of the pattern variables is just a naming convention of
individual programmers. The "?" is the first character of the pattern
variable identifier, not special syntax.
I've tried various naming conventions here, including "?". Once my
macro clauses got large, with a mix of a number of pattern variables as
well as Racket identifiers to be captured, I settled on making the
pattern variable identifiers all-upppercase:
(define-syntax if*
(syntax-rules (then else)
((_ TEST (then CONSEQUENT) (else ALTERNATE))
(if TEST CONSEQUENT ALTERNATE))))
This example is too small too appreciate the difference, with "if" being
the only Racket identifier. Imagine you had a "syntax-rules" clause
with block of code with 20 Racket identifiers in it, and 3 pattern
variables. You'd want the pattern variables scattered throughout this
to really stand out. At least on my screen, all-caps does that better
than "?", and all-caps also takes up less horizontal space, which can
get to be an issue with patterns that you're trying to keep to a single
line for readability symmetries. Anyone else looking at the code will
instantly see which convention you're using, so you can use whatever you
want.
I have a few more useful conventions for "syntax-rules", from which
people can pick&choose depending on the situation and preferences, but
no time today to type them. Typing them up might have to wait for
pounding out a chapter of my tentative practical Racket book. (Not
trying to sell anything; book will be free in Scribble format, probably
as a PLaneT package that installs the book into your searchable local
copies of Racket documentation.)
--
http://www.neilvandyke.org/
_________________________________________________
For list-related administrative tasks:
http://lists.racket-lang.org/listinfo/users
