i need a way to escape not only the current call of a recursive function
(it is already done) but alls:
example:
(def (foo n)
(cond ((= n 0) 'end0)
((= n 7) (return 'end7))
(else (cons n (foo {n - 1})))))
cheme@(guile-user)> (foo 5)
(5 4 3 2 1 . end0)
scheme@(guile-user)> (foo 10)
(10 9 8 . end7)
it has just escaped from the current call to foo
(def (bar n)
(cond ((= n 0) 'end0)
((= n 7) (return-rec 'end7))
(else (cons n (bar {n - 1})))))
scheme@(guile-user)> (bar 5)
(5 4 3 2 1 . end0)
scheme@(guile-user)> (bar 10)
ice-9/boot-9.scm:1669:16: In procedure raise-exception:
Unbound variable: return-rec
i admit i should read the K. Dybvig macro paper but still had not
completely do it.
i modify this code of my Scheme+ but it fails on (bar 10) :
(define-syntax def
(lambda (stx)
(syntax-case stx ()
;; multiple definitions without values assigned
;; (def (x y z))
((_ (var1 ...)) #`(begin (define var1 '()) ...))
;; (def (foo) (when #t (return "hello") "bye"))
;; ((_ (<name> <arg> ...) <body> <body>* ...)
;; (let ((ret-id (datum->syntax stx 'return)))
;; #`(define (<name> <arg> ...)
;; (call/cc (lambda (#,ret-id) <body> <body>* ...)))))
((_ (<name> <arg> ...) <body> <body>* ...)
(let ((ret-id (datum->syntax stx 'return))
(ret-rec-id (datum->syntax stx 'return-rec)))
#`(define (<name> <arg> ...)
(define (<name> <arg> ...)
(call/cc (lambda (#,ret-id) <body> <body>* ...)))
(call/cc (lambda (#,ret-rec-id)
(<name> <arg> ...))))))
;; single definition without a value assigned
;; (def x)
((_ var) #`(define var '()))
;; (def x 7)
((_ var expr) #`(define var expr))
((_ err ...) #`(syntax-error "Bad def form"))
)))
i'am even surprised it works on (bar 5)
if someone had a solution to this problem i will again copy/paste it in my
code and gracefully thanks him a lot :-)
best regards,
damien
