X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=assignment_3_evaluator.mdwn;h=c910064a790698d67cc27a0dd807b3acca70f3a3;hp=c0af5d017e02f98165f6accc738d3cd8eb886a82;hb=880952bd8862bde3c8e71238097fc2726c244e57;hpb=5ed8a6c84fad085dfab0bb91621c5a887f8802ef

diff --git a/assignment_3_evaluator.mdwn b/assignment_3_evaluator.mdwn
index c0af5d01..c910064a 100644
--- a/assignment_3_evaluator.mdwn
+++ b/assignment_3_evaluator.mdwn
@@ -6,13 +6,13 @@ let true = \x y. x in
 let false = \x y. y in
 let and = \l r. l (r true false) false in
 let make\_pair = \f s g. g f s in
-let fst = true in
-let snd = false in
+let get\_fst = true in
+let get\_snd = false in
 let empty = make\_pair true junk in
-let isempty = \x. x fst in
+let isempty = \x. x get\_fst in
 let make\_list = \h t. make\_pair false (make\_pair h t) in
-let head = \l. isempty l err (l snd fst) in
-let tail = \l. isempty l err (l snd snd) in
+let head = \l. isempty l err (l get\_snd get\_fst) in
+let tail = \l. isempty l err (l get\_snd get\_snd) in
 ;
 ; a list of numbers to experiment on
 let mylist = make\_list 1 (make\_list 2 (make\_list 3 empty)) in
@@ -21,7 +21,7 @@ let mylist = make\_list 1 (make\_list 2 (make\_list 3 empty)) in
 let iszero = \n. n (\x. false) true in
 let succ = \n s z. s (n s z) in
 let mul = \m n s. m (n s) in
-let pred = \n. iszero n 0 (length (tail (n (\p. make\_list junk p) empty))) 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
 let eq = \m n. and (leq m n)(leq n m) in
 ;
@@ -32,6 +32,8 @@ let length = Y (\length l. isempty l 0 (succ (length (tail l)))) in
 ;
 ; synonyms
 let makePair = make\_pair in
+let fst = get\_fst in
+let snd = get\_snd in
 let nil = empty in
 let isNil = isempty in
 let makeList = make\_list in