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Make the undefined value unique.

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Jens Axel Søgaard 2014-08-12 19:52:58 +02:00
parent daa767998a
commit a896cf4abd
1 changed files with 4 additions and 3 deletions
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7
whalesong/lang/kernel.rkt
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@ -40,12 +40,13 @@
;; Custom letrec and letrec-values in order to avoid running ;; Custom letrec and letrec-values in order to avoid running
;; into the (in Racket) newly introduced undefined value. ;; into the (in Racket) newly introduced undefined value.
(provide letrec letrec-values) (provide letrec letrec-values)
(define unique-undefined-value (list '<undefined>))
(define-syntax (letrec stx) (define-syntax (letrec stx)
(syntax-case stx () (syntax-case stx ()
[(_ ([id expr] ...) body ...) [(_ ([id expr] ...) body ...)
(syntax/loc stx (syntax/loc stx
(let ([id '**undefined**] ...) (let ([id unique-undefined-value] ...)
(set! id expr) ... (set! id expr) ...
(let () body ...)))])) (let () body ...)))]))
@ -53,7 +54,7 @@
(syntax-case stx () (syntax-case stx ()
[(_ ([(id ...) expr] ...) body ...) [(_ ([(id ...) expr] ...) body ...)
(syntax/loc stx (syntax/loc stx
(let ([id '**undefined**] ... ...) (let ([id unique-undefined-value] ... ...)
(set!-values (id ...) expr) ... (set!-values (id ...) expr) ...
(let () body ...)))])) (let () body ...)))]))