X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=assignment_3_evaluator.mdwn;h=aba94f89cd0a21404f6e7fc51c119cd24e0baaba;hp=496003d08e11017e54aa4324e7f04a521ce2a60b;hb=0a9b2c5fb1adfa3b87e95fcbf26ee79d57ae7466;hpb=6a60dbeb81ccc4949724a6db13a264a0b322a22d

diff --git a/assignment_3_evaluator.mdwn b/assignment_3_evaluator.mdwn
index 496003d0..aba94f89 100644
--- a/assignment_3_evaluator.mdwn
+++ b/assignment_3_evaluator.mdwn
@@ -5,6 +5,8 @@ Here are the definitions pre-loaded for working on assignment 3:
 let true = \x y. x in
 let false = \x y. y in
 let and = \l r. l (r true false) false in
+let or = \l r. l true r in
+;
 let make\_pair = \f s g. g f s in
 let get\_fst = true in
 let get\_snd = false in
@@ -20,15 +22,16 @@ 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 add = \l r. l succ r 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
+let fold = Y (\f l g z. isempty l z (g (head l)(f (tail l) g z))) in
 ;
 ; synonyms
 let makePair = make\_pair in
@@ -40,7 +43,27 @@ let makeList = make\_list in
 let isZero = iszero in
 let mult = mul in
 ;
-length (tail mylist)
+let t1 = (make\_list 1 empty) in
+let t2 = (make\_list 2 empty) in
+let t3 = (make\_list 3 empty) in
+let t12 = (make\_list t1 (make\_list t2 empty)) in
+let t23 = (make\_list t2 (make\_list t3 empty)) in
+let ta = (make\_list t1 t23) in
+let tb = (make\_list t12 (make\_list t3 empty)) in
+let tc = (make\_list t1 (make\_list t23 empty)) in
+;
+;sum-leaves t1 ; ~~> 1
+;sum-leaves t2 ; ~~> 2
+;sum-leaves t3 ; ~~> 3
+;sum-leaves t12 ; ~~> 3
+;sum-leaves t23 ; ~~> 5
+;sum-leaves ta ; ~~> 6
+;sum-leaves tb ; ~~> 6
+;sum-leaves tc ; ~~> 6 
+;
+; updated: added add, and fold for v1 lists; and defn of tb fixed
+; hint: 
+fold mylist add 0
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