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(while): Rewrite, continue as proper escape, break

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without return value, break and continue new for each while form,
don't depend on bindings in expansion environment.
This commit is contained in:
Kevin Ryde 2003-08-12 21:38:21 +00:00
parent 88a63bfc10
commit 773abfbb81
1 changed files with 20 additions and 12 deletions
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32
ice-9/boot-9.scm
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@ -2491,18 +2491,6 @@
(loop (1- count) (cons count result)))))
;;; {While}
;;;
;;; with `continue' and `break'.
;;;
(defmacro while (cond . body)
`(letrec ((continue (lambda () (or (not ,cond) (begin (begin ,@ body) (continue)))))
(break (lambda val (apply throw 'break val))))
(catch 'break
(lambda () (continue))
(lambda v (cadr v)))))
;;; {collect}
;;;
;;; Similar to `begin' but returns a list of the results of all constituent
@ -2560,6 +2548,26 @@
(else
(error "define-syntax-macro can only be used at the top level")))))
;;; {While}
;;;
;;; with `continue' and `break'.
;;;
;; The inner `do' loop avoids re-establishing a catch every iteration,
;; that's only necessary if continue is actually used.
;;
(define-macro (while cond . body)
(let ((key (make-symbol "while-key")))
`(,do ((break ,(lambda () (throw key #t)))
(continue ,(lambda () (throw key #f))))
((,catch (,quote ,key)
(,lambda ()
(,do ()
((,not ,cond))
,@body)
#t)
,(lambda (key arg) arg))))))
;;; {Module System Macros}
;;;