edits

[lambda.git] / assignment3.mdwn

diff --git a/assignment3.mdwn b/assignment3.mdwn
index f84d07f..4da627a 100644 (file)
--- a/assignment3.mdwn
+++ b/assignment3.mdwn
@@ -1,6 +1,19 @@
 Assignment 3
 ------------
 
+Erratum corrected 11PM Sun 3 Oct: the following line
+
+       let tb = (make_list t12 (make_list t3 empty)) in
+
+originally read 
+
+       let tb = (make_list t12 t3) in
+
+This has been corrected below, and in the preloaded evaluator for 
+working on assignment 3.
+
+
+
 Once again, the lambda evaluator will make working through this
 assignment much faster and more secure.
 
@@ -30,7 +43,7 @@ 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
        
@@ -117,7 +130,7 @@ Expected behavior:
        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 tb = (make_list t12 (make_list t3 empty)) in
        let tc = (make_list t1 (make_list t23 empty)) in
 
        sum-leaves t1 ~~> 1