X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=lambda_library.mdwn;h=0c00c4508e5f7d62c4b79086aec13cfc30769229;hp=bdd016875c302e314ae06f632183fd62937c7f19;hb=9e49e4a8db892623d6f3dd202aad27a8547ad826;hpb=c675006fcaa7ef7f096b0cf8e73e28ecb79aa1a9

diff --git a/lambda_library.mdwn b/lambda_library.mdwn
index bdd01687..0c00c450 100644
--- a/lambda_library.mdwn
+++ b/lambda_library.mdwn
@@ -63,8 +63,12 @@ and all sorts of other places. Others of them are our own handiwork.
 	; very inefficient but correct reverse
 	let reverse = \lst. lst (\h sofar. append sofar (singleton h)) empty  in ; or
 	; more efficient reverse builds a left-fold instead
-	; (make_left_list a (make_left_list b (make_left_list c empty)) ~~> \f z. f c (f b (f a z))
+	; make_left_list a (make_left_list b (make_left_list c empty)) ~~> \f z. f c (f b (f a z))
 	let reverse = (\make_left_list lst. lst make_left_list empty) (\h t f z. t f (f h z))  in
+	; most elegant
+	; revappend [a;b;c] [x;y] ~~> [c;b;a;x;y]
+	let revappend = \lst. lst (\hd sofar. \lst. sofar (make_list hd lst)) I  in
+	let rev = \lst. revappend lst empty  in
 	; zip [a;b;c] [x;y;z] ~~> [(a,x);(b,y);(c,z)]
 	let zip = \left right. (\base build. reverse left build base (\x y. reverse x))
                        ; where base is
@@ -237,8 +241,9 @@ and all sorts of other places. Others of them are our own handiwork.
 
 
 	; now you can search for primes, do encryption :-)
-	let gcd = Y (\gcd m n. iszero n m (gcd n (mod m n))) in
-	let lcm = \m n. or (iszero m) (iszero n) 0 (mul (div m (gcd m n)) n) in
+	let gcd = Y (\gcd m n. iszero n m (gcd n (mod m n)))  in ; or
+	let gcd = \m n. iszero m n (Y (\gcd m n. iszero n m (lt n m (gcd (sub m n) n) (gcd m (sub n m)))) m n)  in
+	let lcm = \m n. or (iszero m) (iszero n) 0 (mul (div m (gcd m n)) n)  in
 
 
 	; length for version 1 lists
@@ -324,5 +329,9 @@ let list_equal =
                 )
                 ; when fold is finished, check sofar-pair
                 (\might_be_equal right_tail. and might_be_equal (isempty right_tail))
+
+; most elegant
+let list_equal = \lst. lst (\hd sofar. \lst. and (and (not (isempty lst)) (eq hd (head lst))) (sofar (tail lst))) isempty
+
 -->