zipper module

gistfile1.fs

[<CompilationRepresentation(CompilationRepresentationFlags.ModuleSuffix)>]
module Zipper =
   let up z =  match z.path with
               | (d,v,other)::ep ->  match d with 
                                       | TDirection.Left  -> {focus=Branch(v,z.focus,other); path=ep}
                                       | TDirection.Right -> {focus=Branch(v,other,z.focus); path=ep}
               | []        -> failwith "can't go up" // because ep only goes down and is empty 

   let rec top z  =  match z.path with [] -> z | _  -> top (up z)

   let left z  =   match z.focus with
                          | (Branch(v, l, r)) ->  let v, explored, other = v, l, r 
                                                  {focus=explored; path=((TDirection.Left, v, other)::z.path)}
                          | Leaf -> failwith "can't go down on leaf"

   let right z =  match z.focus with
                          | (Branch(v, l, r)) ->  let v, explored, other = v, r, l 
                                                  {focus=explored; path=((TDirection.Right, v, other)::z.path)}
                          | Leaf -> failwith "can't go down on leaf"

   let rec move (p:ZDirection list) (z:'a Zipper) =
      match p with 
      | []    -> z 
      | d::xs -> match d with 
                  | Up    -> move xs (up z)
                  | Left  -> move xs (left z)
                  | Right -> move xs (right z)
   let fromTree t = {focus = t; path = []}