Re: [Chicken-hackers] What happened to -strict-letrecs?

[John Cowan]

Alex Shinn scripsit:

> The current letrec behavior is a perfectly compliant
> interpretation of R5RS.  There is another compliant
> interpretation which would signal an error in some cases.

Here are the relevant bits of code from SISC's r5rs_pitfall.scm:

;;Credits to Al Petrofsky
;; In thread:
;; defines in letrec body 
;; http://groups.google.com/groups?selm=87bsoq0wfk.fsf%40app.dial.idiom.com
(should-be 1.1 0
 (let ((cont #f))
   (letrec ((x (call-with-current-continuation (lambda (c) (set! cont c) 0)))
            (y (call-with-current-continuation (lambda (c) (set! cont c) 0))))
     (if cont
         (let ((c cont))
           (set! cont #f)
           (set! x 1)
           (set! y 1)
           (c 0))
         (+ x y)))))

;;Credits to Al Petrofsky
;; In thread:
;; Widespread bug (arguably) in letrec when an initializer returns twice
;; http://groups.google.com/groups?selm=87d793aacz.fsf_-_%40app.dial.idiom.com
(should-be 1.2 #t
  (letrec ((x (call/cc list)) (y (call/cc list)))
    (cond ((procedure? x) (x (pair? y)))
          ((procedure? y) (y (pair? x))))
    (let ((x (car x)) (y (car y)))
      (and (call/cc x) (call/cc y) (call/cc x)))))

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