This worked! Thanks On Fri, May 10, 2019 at 10:12 AM Taylor R Campbell <campb...@mumble.net> wrote:
> > Date: Fri, 10 May 2019 01:28:15 -0400 > > From: Nicholas Papadonis <nick.papadonis...@gmail.com> > > > > 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. > > Try (force r) instead of r. >
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