X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=assignment_3_evaluator.mdwn;h=e357bb54a92f3cc972305a23b5ab52ba831af6ed;hp=252e27f5792073500a831749556753a335b58f41;hb=b77bb678d30bbc972f6daf6e6152640faf8f5894;hpb=78a38c6d3d7956c0fb5be8fbc9cbf307ca99a35c

diff --git a/assignment_3_evaluator.mdwn b/assignment_3_evaluator.mdwn
index 252e27f5..e357bb54 100644
--- a/assignment_3_evaluator.mdwn
+++ b/assignment_3_evaluator.mdwn
@@ -1,28 +1,45 @@
 Here are the definitions pre-loaded for working on assignment 3:
 
 <textarea id="INPUT" style="border: 2px solid black; color: black; font-family: monospace; height: 3in; overflow: auto; padding: 0.5em; width: 100%;">
-let true = \x y. x in
-let false = \x y. y in
-let and = \l r. l (r true false) false in
-let makePair = \f s g. g f s in
-let fst = true in
-let snd = false in
-let nil = makePair true meh in
-let isNil = \x. x fst in
-let makeList = \h t. makePair false (makePair h t) in
-let head = \l. isNil l err (l snd fst) in
-let tail = \l. isNil l err (l snd snd) in
-let mylist = makeList 1 (makeList 2 (makeList 3 nil)) in
-let Y = \f. (\h. f (h h)) (\h. f (h h)) in
-let isZero = \n. n (\x. false) true in
-let succ = \n s z. s (n s z) in
-let mult = \m n s. m (n s) in
-let length = Y (\length l. isNil l 0 (succ (length (tail l)))) in
-let pred = \n. isZero n 0 (length (tail (n (\p. makeList meh p) nil))) in
-let leq = \m n. isZero(n pred m) in
-let eq = \m n. and (leq m n)(leq n m) in
-%
-length (tail mylist)
+	; 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
+	
+	; a list of numbers to experiment on
+	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 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 nil = empty in
+	let isNil = isempty in
+	let makeList = make_list in
+	let isZero = iszero in
+	let mult = mul in
+	
+	;
+	length (tail mylist)
 </textarea>
 <input id="PARSE" value="Normalize" type="button">
 <input id="ETA" type="checkbox">do eta-reductions too