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pl:prolog:pllib:means-ends [2019/06/27 15:50] |
pl:prolog:pllib:means-ends [2019/06/27 15:50] (aktualna) |
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| + | ====== Means-ends ====== | ||
| + | {{tag>planning}} | ||
| + | ===== Description ===== | ||
| + | A simple means-ends planner. | ||
| + | |||
| + | **Source**: PROLOG programming for artificial intelligence, 3rd Edition, Harlow, 2001, ISBN 0-201-40375-7. | ||
| + | ===== Download ===== | ||
| + | Program source code: {{means-ends.pl}} | ||
| + | ===== Listing ===== | ||
| + | <code prolog> | ||
| + | % Figure 17.5 A simple means-ends planner. | ||
| + | |||
| + | :- 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 simple means-ends planner | ||
| + | % plan( State, Goals, Plan, FinalState) | ||
| + | |||
| + | plan( State, Goals, [], State) :- % Plan is empty | ||
| + | satisfied( State, Goals). % Goals true in State | ||
| + | |||
| + | % The way plan is decomposed into stages by conc, the | ||
| + | % precondition plan (PrePlan) is found in breadth-first | ||
| + | % fashion. However, the length of the rest of plan is not | ||
| + | % restricted and goals are achieved in depth-first style. | ||
| + | |||
| + | plan( State, Goals, Plan, FinalState) :- | ||
| + | conc( PrePlan, [Action | PostPlan], Plan), % Divide plan | ||
| + | select( State, Goals, Goal), % Select a goal | ||
| + | achieves( Action, Goal), % Relevant action | ||
| + | can( Action, Condition), | ||
| + | plan( State, Condition, PrePlan, MidState1), % Enable Action | ||
| + | apply( MidState1, Action, MidState2), % Apply Action | ||
| + | plan( MidState2, Goals, PostPlan, FinalState). % Achieve remaining goals | ||
| + | |||
| + | % satisfied( State, Goals): Goals are true in State | ||
| + | |||
| + | satisfied( State, []). | ||
| + | |||
| + | satisfied( State, [Goal | Goals]) :- | ||
| + | member( Goal, State), | ||
| + | satisfied( State, Goals). | ||
| + | |||
| + | select( State, Goals, Goal) :- | ||
| + | member( Goal, Goals), | ||
| + | not member( Goal, State). % Goal not satisfied already | ||
| + | |||
| + | % achieves( Action, Goal): Goal is add-list of Action | ||
| + | |||
| + | achieves( Action, Goal) :- | ||
| + | adds( Action, Goals), | ||
| + | member( Goal, Goals). | ||
| + | |||
| + | % apply( State, Action, NewState): Action executed in State produces NewState | ||
| + | |||
| + | apply( State, Action, NewState) :- | ||
| + | deletes( Action, DelList), | ||
| + | delete_all( State, DelList, State1), !, | ||
| + | adds( Action, AddList), | ||
| + | conc( AddList, State1, NewState). | ||
| + | |||
| + | % delete_all( L1, L2, Diff) if Diff is set-difference of 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). | ||
| + | |||
| + | </code> | ||
| + | ===== Comments ===== | ||
