Does anyone know the proper code for a Y-combinator in Scheme that takes an
additional argument? I tried the following solutions. The non-tail
recursive implementation works, however the tail recursive implementaiton
fails. Appreciate any guidance here. Thanks
;; Y-combinator
(define Y
(lambda (f)
((lambda (x) (f (delay (x x))))
(lambda (x) (f (delay (x x)))))))
;Value: y
;; end Y-combinator
;; non-tail recursive, works
((Y (lambda (r)
(lambda (x)
(if (< x 2)
1
(* x ((force r) (- x 1)))))))
5)
;Value: 120
;; Tail reclusive implication, fails.
((Y (lambda (r)
(lambda (x acc)
(if (< x 2)
acc
(r (- x 1) (* x acc))))))
5 1)
;The object #[promise 18] is not applicable.
;; Z-combinator. works.
(define Z
(lambda (f)
((lambda (g) (f (g g)))
(lambda (g) (f (lambda args (apply (g g)
args)))))))
;Value: z
((Z (lambda (r)
(lambda (x)
(if (< x 2)
1
(* x (r (- x 1))))))) 5)
;Value: 120
;; end Z-combinator
Nick
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