Regression planner

Description

A planner based on goal regression.

Source: PROLOG programming for artificial intelligence, 3rd Edition, Harlow, 2001, ISBN 0-201-40375-7.

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Program source code: regression_planner.pl

Listing

%   Figure  17.8  A planner based on goal regression. 
 
%   This planner searches in iterative-deepening style.
 
 
 
:- op( 900, fy, not).
 
 
 
% not Goal): negation as failure; 
 
%   Note: This is often available as a built-in predicate,
 
%   often written as prefix operator "\+", e.g. \+ likes(mary,snakes)
 
 
 
not Goal  :-
 
  Goal, !, fail
 
  ; 
 
  true.
 
 
 
%   A means-ends planner with goal regression
 
%   plan( State, Goals, Plan)
 
plan( State, Goals, [])  :-
 
  satisfied( State, Goals).                   % Goals true in State
 
 
 
plan( State, Goals, Plan)  :-
 
  conc( PrePlan, [Action], Plan),             % Divide plan achieving breadth-first effect
 
  select( State, Goals, Goal),                % Select a goal
 
  achieves( Action, Goal),
 
  can( Action, Condition),                    % Ensure Action contains no variables
 
  preserves( Action, Goals),                  % Protect Goals
 
  regress( Goals, Action, RegressedGoals),    % Regress Goals through Action
 
  plan( State, RegressedGoals, PrePlan).
 
 
 
satisfied( State, Goals)  :-
 
  delete_all( Goals, State, []).              % All Goals in State
 
 
 
select( State, Goals, Goal)  :-               % Select Goal from Goals
 
  member( Goal, Goals).                       % A simple selection principle
 
 
 
achieves( Action, Goal)  :-
 
  adds( Action, Goals),
 
  member( Goal, Goals).
 
 
 
preserves( Action, Goals)  :-                 % Action does not destroy Goals
 
  deletes( Action, Relations),
 
  not (member( Goal, Relations),
 
       member( Goal, Goals) ).
 
 
 
regress( Goals, Action, RegressedGoals)  :-       % Regress Goals through Action
 
  adds( Action, NewRelations),
 
  delete_all( Goals, NewRelations, RestGoals),
 
  can( Action, Condition),
 
  addnew( Condition, RestGoals, RegressedGoals).  % Add precond., check imposs.
 
 
 
% addnew( NewGoals, OldGoals, AllGoals):
 
%   OldGoals is the union of NewGoals and OldGoals
 
%   NewGoals and OldGoals must be compatible
 
 
 
addnew( [], L, L).
 
 
 
addnew( [Goal | _], Goals, _)  :-
 
  impossible( Goal, Goals),         % Goal incompatible with Goals
 
  !, 
 
  fail.                             % Cannot be added
 
 
 
addnew( [X | L1], L2, L3)  :-
 
  member( X, L2),  !,               % Ignore duplicate
 
  addnew( L1, L2, L3).
 
 
 
addnew( [X | L1], L2, [X | L3])  :-
 
  addnew( L1, L2, L3).
 
 
 
% delete_all( L1, L2, Diff): Diff is set-difference of lists L1 and L2
 
 
 
delete_all( [], _, []).
 
 
 
delete_all( [X | L1], L2, Diff)  :-
 
  member( X, L2), !,
 
  delete_all( L1, L2, Diff).
 
 
 
delete_all( [X | L1], L2, [X | Diff])  :-
 
  delete_all( L1, L2, Diff).

Comments

pl/prolog/pllib/regression_planner.txt · ostatnio zmienione: 2017/07/17 08:08 (edycja zewnętrzna)
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