X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=hints%2Fassignment_4_hint_2.mdwn;fp=hints%2Fassignment_4_hint_2.mdwn;h=0000000000000000000000000000000000000000;hp=f9f4cf253a0b938b2d8a877bad7d90dd7051086e;hb=fd698b815e417dec463cb0f0e9ed056ab83daed6;hpb=573a8b36ce653c84c2aecb2b81ef99128cb41d13

diff --git a/hints/assignment_4_hint_2.mdwn b/hints/assignment_4_hint_2.mdwn
deleted file mode 100644
index f9f4cf25..00000000
--- a/hints/assignment_4_hint_2.mdwn
+++ /dev/null
@@ -1,60 +0,0 @@
-Hints for `list_equal`.
-
-*	If `left` is `[]`, what does `right` have to be for `left` and `right` to be equal? (Come on, it's not too hard, you can figure it out.)
-
-*	Suppose on the other hand that `left` has head `left_hd` and tail `left_tl`.
-	
-	<OL type=a>
-	<LI>If `right` is then `[]`, are `left` and `right` equal?
-	<LI>If `right` isn't `[]`, and its head isn't equal to `left_hd`, are `left` and `right` equal?
-	<LI>If `right` isn't `[]` and its head *is* equal to `left_hd`, what else has to be the case for `left` and `right` to be equal?
-	</OL>
-
-*	Can you now write a recursive definition of the `list_equal` function?
-What's your base case?
-
-
-<!--
-let list_equal =
-    \left right. left
-                ; here's our f
-                (\hd sofar.
-                    ; deconstruct our sofar-pair
-                    sofar (\might_be_equal right_tail.
-                        ; our new sofar
-                        make_pair
-                        (and (and might_be_equal (not (isempty right_tail))) (eq? hd (head right_tail)))
-                        (tail right_tail)
-                    ))
-                ; here's our z
-                ; we pass along the fold a pair
-                ; (might_for_all_i_know_still_be_equal?, tail_of_reversed_right)
-                ; when left is empty, the lists are equal if right is empty
-                (make_pair
-                    true ; for all we know so far, they might still be equal
-                    (reverse right)
-                )
-                ; when fold is finished, check sofar-pair
-                (\might_be_equal right_tail. and might_be_equal (isempty right_tail))
--->
-
-<!--
-list_equal [] right      = isempty right
-list_equal (hd:tl) right = and (not (isempty right))
-                            (hd == head right)
-                            (list_equal tl (tail right))
-
-Rearangement:
-
-list_equal []      = \right -> isempty right
-list_equal (hd:tl) = let prev = list_equal tl
-                     in \right -> and (not (isempty right))
-                                   (hd == head right)
-                                   (prev (tail right))
-
-Now it fits the pattern of fold_right
-
-let list_equal = \left. left (\hd sofar. \right. and (and (not (isempty right)) (eq hd (head right))) (sofar (tail right))) isempty
-
--->
-