Hi,
I'm starting to play with syntax-parse. Looks really great, but also quite
complex.
Here are some newbie questions.
(the example is based on the defmac of Eli)
I use two optional declaration:
(define-syntax (defmac2 stx)
(syntax-parse stx
[(defmac2 (name:identifier . xs)
(~optional (~seq #:keywords key:identifier ...))
(~optional (~seq #:captures cap:identifier ...))
body:expr)
#'(define-syntax (name stx)
(syntax-case stx (key ...)
[(name . xs)
(with-syntax ([cap (datum->syntax stx 'cap stx)] ...)
(syntax body))]))])))
1. according to the docs, I can pass #:name in an ~optional.
if I do so:
(~optional (~seq #:keywords key:identifier ...) #:name "foo")
I get:
~optional: unexpected keyword, expected one of (#:defaults) in: #:name
(according to the docs there are 3 keywords for optional, name, too-many, and
defaults)
2. my macro above works ok only if both #:keywords and #:captures are given,
because if they are not, the key and cap variables get bound to #f.
And I get messages like:
key: attribute is bound to non-syntax value: #f in: key
I therefore want to specify a default that is more reasonable than #f in my
case. I looked into the #:defaults parameter of ~optional, but unsuccessfully.
I don't know how to have it behave as I'd expect, that is, if none is given,
then key ... is "zero occurrences".
Any help is greatly appreciated!
Thanks,
-- Éric
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