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pl:prolog:pllib:forward-chaining_rule_interpreter [2019/06/27 15:50] (aktualna) |
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| + | ====== Forward-chaining rule interpreter ====== | ||
| + | {{tag>forward-chaining rules interpreter}} | ||
| + | ===== Description ===== | ||
| + | A forward chaining rule interpreter. | ||
| + | |||
| + | **Source**: PROLOG programming for artificial intelligence, 3rd Edition, Harlow, 2001, ISBN 0-201-40375-7. | ||
| + | ===== Download ===== | ||
| + | Program source code: {{forward-chaining_rule_interpreter.pl}} | ||
| + | ===== Listing ===== | ||
| + | <code prolog> | ||
| + | % Figure 15.7 A forward chaining rule interpreter. | ||
| + | |||
| + | :- 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. | ||
| + | |||
| + | :- op( 800, fx, if). | ||
| + | :- op( 700, xfx, then). | ||
| + | :- op( 300, xfy, or). | ||
| + | :- op( 200, xfy, and). | ||
| + | |||
| + | % Simple forward chaining in Prolog | ||
| + | |||
| + | forward :- | ||
| + | new_derived_fact( P), % A new fact | ||
| + | !, | ||
| + | write( 'Derived: '), write( P), nl, | ||
| + | assert( fact( P)), | ||
| + | forward % Continue | ||
| + | ; | ||
| + | write( 'No more facts'). % All facts derived | ||
| + | |||
| + | new_derived_fact( Concl) :- | ||
| + | if Cond then Concl, % A rule | ||
| + | not fact( Concl), % Rule's conclusion not yet a fact | ||
| + | composed_fact( Cond). % Condition true? | ||
| + | |||
| + | composed_fact( Cond) :- | ||
| + | fact( Cond). % Simple fact | ||
| + | |||
| + | composed_fact( Cond1 and Cond2) :- | ||
| + | composed_fact( Cond1), | ||
| + | composed_fact( Cond2). % Both conjuncts true | ||
| + | |||
| + | composed_fact( Cond1 or Cond2) :- | ||
| + | composed_fact( Cond1) | ||
| + | ; | ||
| + | composed_fact( Cond2). | ||
| + | </code> | ||
| + | ===== Comments ===== | ||
