X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=assignment_3_evaluator.mdwn;h=aba94f89cd0a21404f6e7fc51c119cd24e0baaba;hp=28693f436d9360d5603354a48ecf498e32633e8f;hb=1e70b7849153992272e219477464128c8d97789a;hpb=4cea4f69242f3a229292186c8fa652942f31f8b8

diff --git a/assignment_3_evaluator.mdwn b/assignment_3_evaluator.mdwn
index 28693f43..aba94f89 100644
--- a/assignment_3_evaluator.mdwn
+++ b/assignment_3_evaluator.mdwn
@@ -22,6 +22,7 @@ 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 = (\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
@@ -29,8 +30,8 @@ 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
@@ -42,24 +43,27 @@ let makeList = make\_list in
 let isZero = iszero in
 let mult = mul in
 ;
-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 t3) in
-let tc = (make_list t1 (make_list t23 empty)) in
+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 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 
 ;
-length (tail mylist)
+; updated: added add, and fold for v1 lists; and defn of tb fixed
+; hint: 
+fold mylist add 0
 </textarea>
 
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