Hello all,
I've been playing around with creating circular lists (and learning racket
which has been quite fun), but I'm stumped on why the lazy version of
letrec-values is not producing a promise like the lazy version of letrec
does. With the lazy letrec I can create circular lists, but with the lazy
letrec-values I get #<undefined>. See the example below.
;;;;;;;;;;;;;;;;; example code ;;;;;;;;;;;;;;;;;;;;;;;;;
#lang lazy
;; create a circular list using letrec (this works)
(define example-working
(letrec ([A (list 'a B)]
[B (list 'b A)])
B))
(displayln "Working Example:")
(displayln example-working)
(displayln (!! example-working))
; Prints...
;Working Example:
;(b #<promise:A>)
;#0=(b (a #0#))
;; create a circular list using letrec-values (this is broken)
(define example-broken
(letrec-values ([(A) (values (list 'a B))]
[(B) (values (list 'b A))])
B))
(displayln "Broken Example:")
(displayln example-broken)
(displayln (!! example-broken))
; Prints
;Broken Example:
;(b (a #<undefined>))
;(b (a #<undefined>))
;;;;;;;;;;;;;;;;; end code ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
I realize that there are many different ways to generate circular lists,
but why doesn't this work? Am I misunderstanding something or is this a bug?
Thanks,
Luke
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