X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=assignment3.mdwn;h=e240b732b1405e176d696bbab3c5974a1d125f35;hp=9c0d2d836476078c8aa012a08600b2ed8b5f621d;hb=671e314f91abff10acfa31eab2211bb7eeb17881;hpb=94f47d126b9513c2a198eba685d44030bc31ac1d diff --git a/assignment3.mdwn b/assignment3.mdwn index 9c0d2d83..e240b732 100644 --- a/assignment3.mdwn +++ b/assignment3.mdwn @@ -12,7 +12,7 @@ originally read This has been corrected below, and in the preloaded evaluator for working on assignment 3, available here: [[assignment 3 evaluator]]. - +
Once again, the lambda evaluator will make working through this assignment much faster and more secure. @@ -42,6 +42,7 @@ Recall that version 1 style lists are constructed like this (see ; church numerals let iszero = \n. n (\x. false) true in let succ = \n s z. s (n s z) in + let add = \l r. l succ r in let mul = \m n s. m (n s) in let pred = (\shift n. n shift (make\_pair 0 0) get\_snd) (\p. p (\x y. make\_pair (succ x) x)) in let leq = \m n. iszero(n pred m) in @@ -50,6 +51,7 @@ Recall that version 1 style lists are constructed like this (see ; a fixed-point combinator for defining recursive functions let Y = \f. (\h. f (h h)) (\h. f (h h)) in let length = Y (\length l. isempty l 0 (succ (length (tail l)))) in + let fold = Y (\f l g z. isempty l z (g (head l)(f (tail l) g z))) in eq 2 2 yes no