X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=assignment_3_evaluator.mdwn;h=c910064a790698d67cc27a0dd807b3acca70f3a3;hp=4ffaaa1316634948260b4f1d99355474e2fef213;hb=2950fbdc81547d95aa8fda13cc3e042ca264e0e6;hpb=e52e762c491b3e398fc1a8a6924b100c1bf587fe

diff --git a/assignment_3_evaluator.mdwn b/assignment_3_evaluator.mdwn
index 4ffaaa13..c910064a 100644
--- a/assignment_3_evaluator.mdwn
+++ b/assignment_3_evaluator.mdwn
@@ -1,49 +1,48 @@
 Here are the definitions pre-loaded for working on assignment 3:
 
-<pre>
-<textarea id="INPUT" style="border: 2px solid black;
-color: black; font-family: monospace; height: 3in;
-overflow: auto; padding: 0.5em; width: 100%;">
+<textarea id="INPUT" style="border: 2px solid black; color: black; font-family: monospace; height: 3in; overflow: auto; padding: 0.5em; width: 100%;">
 ; booleans
 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 empty = make_pair true junk in
-let isempty = \x. x 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 make\_pair = \f s g. g f s in
+let get\_fst = true in
+let get\_snd = false in
+let empty = make\_pair true junk 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 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
-
+let mylist = make\_list 1 (make\_list 2 (make\_list 3 empty)) in
+;
 ; church numerals
 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
-
+;
 ; 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
-
+;
 ; synonyms
-let makePair = make_pair in
+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
+let makeList = make\_list in
 let isZero = iszero in
 let mult = mul in
-
+;
 length (tail mylist)
 </textarea>
-</pre>
+
 <input id="PARSE" value="Normalize" type="button">
 <input id="ETA" type="checkbox">do eta-reductions too
 <noscript><p>You may not see it because you have JavaScript turned off. Uffff!</p></noscript>