146 lines
5.7 KiB
Scheme
146 lines
5.7 KiB
Scheme
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#lang scheme/base
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(require scheme/class
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syntax/stx)
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(provide (all-defined-out))
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;; Problem: If stx1 and stx2 are two distinguishable syntax objects, it
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;; still may be the case that (syntax-e stx1) and (syntax-e stx2) are
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;; indistinguishable.
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;; Solution: Rather than map stx to (syntax-e stx), in the cases where
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;; (syntax-e stx) is confusable, map it to a different, unique, value.
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;; - stx is identifier : map it to an uninterned symbol w/ same rep
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;; (Symbols are useful: see pretty-print's style table)
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;; - else : map it to a syntax-dummy object
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;; NOTE: Nulls are only wrapped when *not* list-terminators.
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;; If they were always wrapped, the pretty-printer would screw up
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;; list printing (I think).
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(define-struct syntax-dummy (val))
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;; A SuffixOption is one of
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;; - 'never -- never
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;; - 'always -- suffix > 0
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;; - 'over-limit -- suffix > limit
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;; - 'all-if-over-limit -- suffix > 0 if any over limit
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;; syntax->datum/tables : stx partition% num SuffixOption
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;; -> (values s-expr hashtable hashtable)
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;; When partition is not false, tracks the partititions that subterms belong to
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;; When limit is a number, restarts processing with numbering? set to true
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;;
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;; Returns three values:
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;; - an S-expression
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;; - a hashtable mapping S-expressions to syntax objects
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;; - a hashtable mapping syntax objects to S-expressions
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;; Syntax objects which are eq? will map to same flat values
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(define (syntax->datum/tables stx partition limit suffixopt)
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(table stx partition limit suffixopt))
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;; table : syntax maybe-partition% maybe-num SuffixOption -> (values s-expr hashtable hashtable)
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(define (table stx partition limit suffixopt)
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(define (make-identifier-proxy id)
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(case suffixopt
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((never) (unintern (syntax-e id)))
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((always)
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(let ([n (send partition get-partition id)])
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(if (zero? n) (unintern (syntax-e id)) (suffix (syntax-e id) n))))
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((over-limit)
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(let ([n (send partition get-partition id)])
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(if (<= n limit)
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(unintern (syntax-e id))
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(suffix (syntax-e id) n))))))
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(let/ec escape
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(let ([flat=>stx (make-hasheq)]
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[stx=>flat (make-hasheq)])
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(define (loop obj)
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(cond [(hash-ref stx=>flat obj (lambda _ #f))
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=> (lambda (datum) datum)]
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[(and partition (identifier? obj))
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(when (and (eq? suffixopt 'all-if-over-limit)
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(> (send partition count) limit))
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(call-with-values (lambda () (table stx partition #f 'always))
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escape))
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(let ([lp-datum (make-identifier-proxy obj)])
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(hash-set! flat=>stx lp-datum obj)
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(hash-set! stx=>flat obj lp-datum)
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lp-datum)]
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[(and (syntax? obj) (check+convert-special-expression obj))
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=> (lambda (newobj)
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(when partition (send partition get-partition obj))
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(let* ([inner (cadr newobj)]
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[lp-inner-datum (loop inner)]
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[lp-datum (list (car newobj) lp-inner-datum)])
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(hash-set! flat=>stx lp-inner-datum inner)
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(hash-set! stx=>flat inner lp-inner-datum)
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(hash-set! flat=>stx lp-datum obj)
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(hash-set! stx=>flat obj lp-datum)
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lp-datum))]
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[(syntax? obj)
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(when partition (send partition get-partition obj))
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(let ([lp-datum (loop (syntax-e obj))])
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(hash-set! flat=>stx lp-datum obj)
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(hash-set! stx=>flat obj lp-datum)
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lp-datum)]
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[(pair? obj)
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(pairloop obj)]
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[(symbol? obj)
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(unintern obj)]
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[(null? obj)
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(make-syntax-dummy obj)]
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[(boolean? obj)
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(make-syntax-dummy obj)]
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[(number? obj)
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(make-syntax-dummy obj)]
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[(keyword? obj)
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(make-syntax-dummy obj)]
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[(vector? obj)
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(list->vector (map loop (vector->list obj)))]
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[(box? obj)
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(box (loop (unbox obj)))]
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[else obj]))
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(define (pairloop obj)
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(cond [(pair? obj)
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(cons (loop (car obj))
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(pairloop (cdr obj)))]
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[(null? obj)
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null]
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[(and (syntax? obj) (null? (syntax-e obj)))
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null]
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[else (loop obj)]))
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(values (loop stx)
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flat=>stx
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stx=>flat))))
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;; check+convert-special-expression : syntax -> #f/syntaxish
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(define (check+convert-special-expression stx)
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(define stx-list (stx->list stx))
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(and stx-list (= 2 (length stx-list))
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(let ([kw (car stx-list)]
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[expr (cadr stx-list)])
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(and (identifier? kw)
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(memq (syntax-e kw) special-expression-keywords)
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(bound-identifier=? kw (datum->syntax stx (syntax-e kw)))
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(andmap (lambda (f) (equal? (f stx) (f kw)))
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(list syntax-source
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syntax-line
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syntax-column
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syntax-position
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syntax-original?
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syntax-source-module))
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(cons (syntax-e kw)
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(list expr))))))
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(define special-expression-keywords
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'(quote quasiquote unquote unquote-splicing syntax))
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;; FIXME: quasisyntax unsyntax unsyntax-splicing
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(define (unintern sym)
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(string->uninterned-symbol (symbol->string sym)))
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(define (suffix sym n)
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(string->uninterned-symbol (format "~a:~a" sym n)))
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