194 lines
8.8 KiB
Racket
194 lines
8.8 KiB
Racket
(module current-pvars '#%kernel
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(#%provide (for-syntax current-pvars
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current-pvars+unique)
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with-pvars
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define-pvars)
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(#%require racket/private/small-scheme
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(for-syntax '#%kernel
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racket/private/qq-and-or
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racket/private/stx))
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;; This is a poor man's syntax parameter. Since the implementation of
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;; racket/stxparam depends on syntax-case, and we want to add current-pvars to
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;; syntax-case, we cannot use syntax parameters, lest we create a cyclic
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;; dependency. Instead, we implement here a simplified "syntax parameter".
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; Like racket/stxparam, it relies on nested bindings of the same identifier,
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;; and on syntax-local-get-shadower to access the most nested binding.
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;; Since define/with-syntax and define/syntax-parse need to add new ids to
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;; the list, they redefine current-pvars-param, shadowing the outer binding.
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;; Unfortunately, if a let form contains two uses of define/with-syntax, this
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;; would result in two redefinitions of current-pvars-param, which would cause
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;; a "duplicate definition" error. Instead of shadowing the outer bindings, we
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;; therefore store the list of bound syntax pattern variables in a new, fresh
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;; identifier. When accessing the list, (current-pvars) then checks all such
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;; identifiers. The identifiers have the form current-pvars-paramNNN and are
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;; numbered sequentially, each new "shadowing" identifier using the number
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;; following the latest visible identifier.
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;; When it is safe to shadow identifiers (i.e. for with-pvars, but not for
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;; define-pvars), current-pvars-index-lower-bound is also shadowed.
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;; When current-pvars-index-lower-bound is bound, it contains the index of the
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;; latest current-pvars-paramNNN at that point.
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;; When accessing the latest current-pvars-paramNNN, a dichotomy search is
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;; performed between current-pvars-index-lower-bound and an upper bound
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;; computed by trying to access lower-bound + 2ᵏ, with increasing values of k,
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;; until an unbound identifier is found.
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;; (poor-man-parameterof exact-nonnegative-integer?)
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(define-syntaxes (current-pvars-index-lower-bound) 0)
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;; (poor-man-parameterof (listof identifier?))
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(define-syntaxes (current-pvars-param0) '())
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(begin-for-syntax
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;; (-> any/c (or/c (listof syntax?) #f))
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(define-values (syntax*->list)
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(λ (stxlist)
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(syntax->list (datum->syntax #f stxlist))))
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;; (-> identifier? (or/c #f (listof identifier?)))
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(define-values (try-current-pvars)
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(λ (id)
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(syntax-local-value
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(syntax-local-get-shadower id
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#t)
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;; Default value if we are outside of any with-pvars.
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(λ () #f))))
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;; (-> exact-nonnegative-integer? identifier?)
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(define-values (nth-current-pvars-id)
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(λ (n)
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(syntax-local-introduce
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(datum->syntax (quote-syntax here)
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(string->symbol
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(format "current-pvars-param~a" n))))))
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;; (-> exact-nonnegative-integer? (or/c #f (listof identifier?)))
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(define-values (try-nth-current-pvars)
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(λ (n)
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(try-current-pvars (nth-current-pvars-id n))))
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;; (-> exact-nonnegative-integer? exact-nonnegative-integer?
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;; exact-nonnegative-integer?)
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;; Doubles the value of n until (+ start n) is not a valid index
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;; in the current-pvars-param pseudo-array
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(define-values (double-max)
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(λ (start n)
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(if (try-nth-current-pvars (+ start n))
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(double-max start (* n 2))
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(+ start n))))
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;; (-> exact-nonnegative-integer? exact-nonnegative-integer?
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;; exact-nonnegative-integer?)
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;; Preconditions: upper > lower ∧ upper - lower = 2ᵏ ∧ k ∈ ℕ
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;; Returns the last valid index in the current-pvars-param pseudo-array,
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;; by dichotomy between
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(define-values (dichotomy)
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(λ (lower upper)
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(if (= (- upper lower) 1)
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(if (try-nth-current-pvars upper)
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upper ;; Technically not possible, still included for safety.
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lower)
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(let ([mid (/ (+ upper lower) 2)])
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(if (try-nth-current-pvars mid)
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(dichotomy mid upper)
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(dichotomy lower mid))))))
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;; (-> exact-nonnegative-integer?)
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(define-values (find-last-current-pvars)
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(λ ()
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(let ([lower-bound (syntax-local-value
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(syntax-local-get-shadower
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(syntax-local-introduce
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(quote-syntax current-pvars-index-lower-bound))
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#t))])
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(if (not (try-nth-current-pvars (+ lower-bound 1)))
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;; Short path for the common case where there are no uses
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;; of define/with-syntax or define/syntax-parse in the most nested
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;; syntax-case, with-syntax or syntax-parse
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lower-bound
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;; Find an upper bound by repeatedly doubling an offset (starting
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;; with 1) from the lower bound, then perform a dichotomy between
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;; these two bounds.
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(dichotomy lower-bound
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(double-max lower-bound 1))))))
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;; (-> (listof identifier?))
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(define-values (current-pvars)
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(λ ()
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(map car (try-nth-current-pvars (find-last-current-pvars)))))
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(define-values (current-pvars+unique)
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(λ ()
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(try-nth-current-pvars (find-last-current-pvars)))))
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;; (with-pvars [pvar ...] . body)
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(define-syntaxes (with-pvars)
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(lambda (stx)
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(if (not (and (stx-pair? stx)
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(identifier? (stx-car stx))
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(stx-pair? (stx-cdr stx))
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(syntax*->list (stx-car (stx-cdr stx)))
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(andmap identifier?
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(syntax*->list (stx-car (stx-cdr stx))))))
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(raise-syntax-error 'with-pvars "bad syntax" stx)
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(void))
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(let* ([pvars (reverse (syntax*->list (stx-car (stx-cdr stx))))]
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[unique-at-runtime (map gensym (map syntax-e pvars))]
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[stxquoted-pvars+unique (map (λ (v unique)
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`(cons (quote-syntax ,v)
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(quote-syntax ,unique)))
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pvars
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unique-at-runtime)]
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[body (stx-cdr (stx-cdr stx))]
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[old-pvars-index (find-last-current-pvars)]
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[old-pvars (try-nth-current-pvars old-pvars-index)]
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[binding (syntax-local-identifier-as-binding
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(nth-current-pvars-id (+ old-pvars-index 1)))]
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[lower-bound-binding
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(syntax-local-identifier-as-binding
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(syntax-local-introduce
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(quote-syntax current-pvars-index-lower-bound)))]
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[do-unique-at-runtime (map (λ (id pvar)
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`[(,id) (gensym (quote ,pvar))])
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unique-at-runtime
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pvars)])
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(datum->syntax
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(quote-syntax here)
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`(let-values (,@do-unique-at-runtime)
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(letrec-syntaxes+values
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([(,binding) (list* ,@stxquoted-pvars+unique
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(try-nth-current-pvars ,old-pvars-index))]
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[(,lower-bound-binding) ,(+ old-pvars-index 1)])
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()
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. ,body))))))
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(define-syntaxes (define-pvars)
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(lambda (stx)
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(if (not (and (stx-pair? stx)
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(identifier? (stx-car stx))
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(syntax*->list (stx-cdr stx))
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(andmap identifier?
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(syntax*->list (stx-cdr stx)))))
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(raise-syntax-error 'define-pvars "bad syntax" stx)
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(void))
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(let* ([pvars (reverse (syntax*->list (stx-cdr stx)))]
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[unique-at-runtime (map gensym (map syntax-e pvars))]
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[stxquoted-pvars+unique (map (λ (v unique)
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`(cons (quote-syntax ,v)
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(quote-syntax ,unique)))
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pvars
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unique-at-runtime)]
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[old-pvars-index (find-last-current-pvars)]
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[old-pvars (try-nth-current-pvars old-pvars-index)]
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[binding (syntax-local-identifier-as-binding
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(nth-current-pvars-id (+ old-pvars-index 1)))])
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(datum->syntax
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(quote-syntax here)
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`(begin
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(define-values (,@unique-at-runtime)
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(values ,@(map (λ (pvar) `(gensym (quote ,pvar))) pvars)))
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(define-syntaxes (,binding)
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(list* ,@stxquoted-pvars+unique
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(try-nth-current-pvars ,old-pvars-index))))))))) |