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make it possible to use "start" and "atok" as literal tokens

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tokens
Matthew Butterick 7 years ago
parent 3e71cfa350
commit 2d5d7ecaaf
1 changed files with 39 additions and 27 deletions
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22
parser-tools-lib/parser-tools/cfg-parser.rkt
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@ -489,6 +489,12 @@
(fail-k max-depth tasks))))]) (fail-k max-depth tasks))))])
(k end max-depth tasks new-got-k new-fail-k)))]))))) (k end max-depth tasks new-got-k new-fail-k)))])))))
;; These temp identifiers can't be `gensym` or `generate-temporary`
;; because they have to be consistent between module loads
;; (IIUC, the parser is multi-threaded, and this approach is not thread-safe)
;; so I see no alternative to the old standby of making them ludicrously unlikely
(define-for-syntax start-id-temp 'start_jihqolbbafscgxvsufnepvmxqipnxgmlpxukmdoqxqzmzgaogaftbkbyqjttwwfimifowdxfyekjiixdmtprfkcvfciraehoeuaz)
(define-for-syntax atok-id-temp 'atok_wrutdjgecmybyfipiwsgjlvsveryodlgassuzcargiuznzgdghrykfqfbwcjgzdhdoeqxcucmtjkuyucskzethozhqkasphdwbht)
(define-syntax (cfg-parser stx) (define-syntax (cfg-parser stx)
(syntax-case stx () (syntax-case stx ()
[(_ clause ...) [(_ clause ...)
@ -704,11 +710,17 @@
[(pos ...) [(pos ...)
(if src-pos? (if src-pos?
#'($1-start-pos $1-end-pos) #'($1-start-pos $1-end-pos)
#'(#f #f))]) #'(#f #f))]
#`(grammar (start [() null] ;; rename `start` and `atok` to temp ids
[(atok start) (cons $1 $2)]) ;; so that "start" and "atok" can be used as literal string tokens in a grammar.
(atok [(tok) (make-tok 'tok-id 'tok $e pos ...)] ...))) ;; not sure why this works, but it passes all tests.
#`(start start) [%start start-id-temp]
[%atok atok-id-temp])
#`(grammar (%start [() null]
[(%atok %start) (cons $1 $2)])
(%atok [(tok) (make-tok 'tok-id 'tok $e pos ...)] ...)))
(with-syntax ([%start start-id-temp])
#`(start %start))
parser-clauses)))] parser-clauses)))]
[(grammar . _) [(grammar . _)
(raise-syntax-error (raise-syntax-error

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