matita/matita/contribs/lambda/pointer_tree.ma

   1 (**************************************************************************)
   2 (*       ___                                                              *)
   3 (*      ||M||                                                             *)
   4 (*      ||A||       A project by Andrea Asperti                           *)
   5 (*      ||T||                                                             *)
   6 (*      ||I||       Developers:                                           *)
   7 (*      ||T||         The HELM team.                                      *)
   8 (*      ||A||         http://helm.cs.unibo.it                             *)
   9 (*      \   /                                                             *)
  10 (*       \ /        This file is distributed under the terms of the       *)
  11 (*        v         GNU General Public License Version 2                  *)
  12 (*                                                                        *)
  13 (**************************************************************************)
  14
  15 include "pointer_list.ma".
  16
  17 (* POINTER TREE *************************************************************)
  18
  19 (* Policy: pointer tree metavariables: P, Q *)
  20 (* Note: this is a binary tree on pointer sequences *)
  21 inductive ptrt: Type[0] ≝
  22 | tnil : ptrt
  23 | tcons: ptrl → ptrt → ptrt → ptrt
  24 .
  25
  26 let rec length (P:ptrt) on P ≝ match P with
  27 [ tnil          ⇒ 0
  28 | tcons s Q1 Q2 ⇒ length Q2 + length Q1 + |s|
  29 ].
  30
  31 interpretation "pointer tree length" 'card P = (length P).