fixed assignment3 pred

Signed-off-by: Jim Pryor <profjim@jimpryor.net>

diff --git a/assignment3.mdwn b/assignment3.mdwn
index f84d07f..289f818 100644 (file)
--- a/assignment3.mdwn
+++ b/assignment3.mdwn
@@ -30,7 +30,7 @@ Recall that version 1 style lists are constructed like this (see
        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 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
        

diff --git a/assignment_3_evaluator.mdwn b/assignment_3_evaluator.mdwn
index 496003d..c910064 100644 (file)
--- a/assignment_3_evaluator.mdwn
+++ b/assignment_3_evaluator.mdwn
@@ -21,7 +21,7 @@ let mylist = make\_list 1 (make\_list 2 (make\_list 3 empty)) in
 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 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
 ;