Here's one way: (~and z:id (~fail #:unless (free-identifier=? #'z #'zeta) "expected the identifier `zeta`"))
Another way is to make a syntax class (either specifically for `zeta` or parameterized by the identifier) that does the same check.
Ryan On 4/3/18 8:33 AM, Matthew Butterick wrote:
Consider the difference in results below. How would I persuade `syntax-parse` to match literal identifiers in the `free-identifier=?` sense that `syntax-case` does? (and thereby allow unbound identifiers to be compared also) IIUC, `#:literals` is too strict, as it insists that every listed identifier have a binding; `#:datum-literals` is too lenient, as it does not compare bindings at all, but rather just the symbol. ;;;;;;;;;;;;;;;;;;;;;;;;; #lang racket (require math rackunit) (module mod racket (require (for-syntax syntax/parse)) (define-syntax (mac stx) (syntax-parse stx #:literals () ;; <- can't put `zeta` here, produces an error #:datum-literals (zeta) [(_ zeta) #''match] [else #''nope])) (provide mac)) (require 'mod) (check-equal? (mac zeta) 'match) (module mod2 racket (require (for-syntax syntax/parse)) (define-syntax (mac2 stx) (syntax-case stx (zeta) [(_ zeta) #''match] [else #''nope])) (provide mac2)) (require 'mod2) (check-equal? (mac2 zeta) 'nope)
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