X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?a=blobdiff_plain;f=arithmetic.mdwn;h=beedc2874eeaa662e21006803bf59321567cbce3;hb=6dcf7995023877c6946a45657126ead9266dcb40;hp=bc15ae8de777a3ad40fe126cbe7500f02edd4890;hpb=cbb48495bd8cd6cdcbebd1bcd8c3051148c8b0a6;p=lambda.git

diff --git a/arithmetic.mdwn b/arithmetic.mdwn
index bc15ae8d..beedc287 100644
--- a/arithmetic.mdwn
+++ b/arithmetic.mdwn
@@ -37,15 +37,31 @@ Here are a bunch of pre-tested operations for the untyped lambda calculus. In so
 	let make_list = \h t f z. f h (t f z)  in
 	let isempty = \lst. lst (\h sofar. false) true  in
 	let head = \lst. lst (\h sofar. h) junk  in
-	let tail = \lst. (\shift lst. lst shift (make_pair empty junk) get_2nd)
+	let tail_empty = empty  in
+	let tail = \lst. (\shift. lst shift (make_pair empty tail_empty) get_2nd)
 				; where shift is
 				(\h p. p (\t y. make_pair (make_list h t) t))  in
 	let length = \lst. lst (\h sofar. succ sofar) 0  in
 	let map = \f lst. lst (\h sofar. make_list (f h) sofar) empty  in
 	let filter = \f lst. lst (\h sofar. f h (make_list h sofar) sofar) empty  in ; or
 	let filter = \f lst. lst (\h. f h (make_list h) I) empty  in
-	let reverse = \lst. lst (\h t. t make_list (\f n. f h n)) empty  in
-	
+
+	; append list2 to list1 with: list1 make_list list2
+	let singleton = \x f z. f x z  in
+	let reverse = \lst. lst (\h sofar. sofar make_list (singleton h)) 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
+                       (make_pair empty (map (\h u. u h) right))
+                       ; and build is
+                       (\h sofar. sofar (\x y. isempty y
+                                               sofar
+                                               (make_pair (make_list (\u. head y (u h)) x)  (tail y))
+                       ))  in
+
+	let all = \f lst. lst (\h sofar. and sofar (f h)) true  in
+	let any = \f lst. lst (\h sofar. or sofar (f h)) false  in
+
 
 	; version 1 lists