+++ /dev/null
-1. Complete the definitions of `move_botleft` and `move_right_or_up` from the same-fringe solution in the [[week11]] notes. Test your attempts against some example trees to see if the resulting `make_fringe_enumerator` and `same_fringe` functions work as expected.
-
- type 'a tree = Leaf of 'a | Node of ('a tree * 'a tree)
-
- type 'a starred_tree = Root | Starring_Left of 'a starred_pair | Starring_Right of 'a starred_pair
- and 'a starred_pair = { parent : 'a starred_tree; sibling: 'a tree }
- and 'a zipper = { tree : 'a starred_tree; filler: 'a tree };;
-
- let rec move_botleft (z : 'a zipper) : 'a zipper =
- (* returns z if the targetted node in z has no children *)
- (* else returns move_botleft (zipper which results from moving down and left in z) *)
- YOU SUPPLY THE DEFINITION
-
-
- let rec move_right_or_up (z : 'a zipper) : 'a zipper option =
- (* if it's possible to move right in z, returns Some (the result of doing so) *)
- (* else if it's not possible to move any further up in z, returns None *)
- (* else returns move_right_or_up (result of moving up in z) *)
- YOU SUPPLY THE DEFINITION
-
-
- let new_zipper (t : 'a tree) : 'a zipper =
- {tree = Root; filler = t}
- ;;
-
- let make_fringe_enumerator (t: 'a tree) =
- (* create a zipper targetting the root of t *)
- let zstart = new_zipper t
- in let zbotleft = move_botleft zstart
- (* create a refcell initially pointing to zbotleft *)
- in let zcell = ref (Some zbotleft)
- (* construct the next_leaf function *)
- in let next_leaf () : 'a option =
- match !zcell with
- | None -> (* we've finished enumerating the fringe *)
- None
- | Some z -> (
- (* extract label of currently-targetted leaf *)
- let Leaf current = z.filler
- (* update zcell to point to next leaf, if there is one *)
- in let () = zcell := match move_right_or_up z with
- | None -> None
- | Some z' -> Some (move_botleft z')
- (* return saved label *)
- in Some current
- )
- (* return the next_leaf function *)
- in next_leaf
- ;;
-
- let same_fringe (t1 : 'a tree) (t2 : 'a tree) : bool =
- let next1 = make_fringe_enumerator t1
- in let next2 = make_fringe_enumerator t2
- in let rec loop () : bool =
- match next1 (), next2 () with
- | Some a, Some b when a = b -> loop ()
- | None, None -> true
- | _ -> false
- in loop ()
- ;;
-