I'm trying to learn how to write syntax classes. My intended macro expresses a
set of Racket versions, either as inclusive intervals or as exact versions. In
an interval, "*" remove a bound.
- (version "6.5") means exactly version "6.5", as does (version ("6.5" "6.5"))
- (versions ("7.0" "7.7.0.5")) means the inclusive interval between version 7.0
and 7.7.0.5
- (versions ("7.0" "7.7.0.5") "6.5"): union of the above two items
- (versions ("6.0" "*")): all Racket versions >= 6.0
- (versions "*"), (versions ("*" "*")): all Racket versions
I was able to define the syntax class without much issue:
(define-syntax-class racket-version-selection
#:attributes (min max)
(pattern (min:string max:string))
(pattern (~and (~var v string)
(~bind [min #'v]
[max #'v]))))
Now I want each attribute-bound expression V to satisfy (or (valid-version? V)
(equal? V "*")). Where I'm stuck is how I can use #:declare with (expr/c) here.
From what I understand, expr/c does not really mean much because it accepts an
expression (as in the expr syntax-class), not attributes.
The only way I can think to fix this is to perform an additional syntax-parse
so that I can use the attributes in an expression for expr/c to consume. But is
it possible to do everything I'm thinking of in just one syntax class?
~slg
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