hints/assignment_4_hint_2.mdwn

   1 Hints for list\_equal.
   2
   3 <!--
   4 let list_equal =
   5     \left right. left
   6                 ; here's our f
   7                 (\hd sofar.
   8                     ; deconstruct our sofar-pair
   9                     sofar (\might_be_equal right_tail.
  10                         ; our new sofar
  11                         make_pair
  12                         (and (and might_be_equal (not (isempty right_tail))) (eq? hd (head right_tail)))
  13                         (tail right_tail)
  14                     ))
  15                 ; here's our z
  16                 ; we pass along the fold a pair
  17                 ; (might_for_all_i_know_still_be_equal?, tail_of_reversed_right)
  18                 ; when left is empty, the lists are equal if right is empty
  19                 (make_pair
  20                     true ; for all we know so far, they might still be equal
  21                     (reverse right)
  22                 )
  23                 ; when fold is finished, check sofar-pair
  24                 (\might_be_equal right_tail. and might_be_equal (isempty right_tail))
  25 -->