tweak calc improvements

[lambda.git] / assignment3.mdwn

diff --git a/assignment3.mdwn b/assignment3.mdwn
index 9c0d2d8..e240b73 100644 (file)
--- 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]].
 
-
+<hr>
 
 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