Here is a syntax-parse macro that requires one subexpression to be
wrapped with an exclamation point.
(define-syntax (test stx)
(syntax-parse stx #:datum-literals (!)
[((~or (~once (! x:expr) #:name "!")
(~not (! y:expr))) ...)
#'42]))
Everything works like I would expect:
(test (! 1) (! 2)) => test: too many occurrences of ! in: ()
(test (! 1) 2) => 42
(test 1 2) => test: missing required occurrence of ! in: ()
Here is the same macro but with an extra ~seq and an extra pair of
parens around the pattern:
(define-syntax (test stx)
(syntax-parse stx #:datum-literals (!)
[((~seq (~or (~once (! x:expr) #:name "!")
(~not (! y:expr))) ...))
#'42]))
Here are the same tests:
(test (! 1) (! 2)) => test: too many occurrences of ! in: ()
(test (! 1) 2) => 42
(test 1 2) => test: bad syntax in: (test 1 2)
I expected the same outputs as the first macro, but the last test
example only reports "bad syntax" and not "too few". Is this expected
behavior that I'm not understanding or a bug?
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