58 lines
1.8 KiB
Kotlin
58 lines
1.8 KiB
Kotlin
package prolog.ast.logic
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import prolog.Answers
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import prolog.Substitutions
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import prolog.ast.terms.Functor
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import prolog.ast.terms.Goal
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/**
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* Collection of [Clause]s with the same [Functor].
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*
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* If a goal is proved, the system looks for a predicate with the same functor, then uses indexing
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* to select candidate clauses and then tries these clauses one-by-one.
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*/
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class Predicate : Resolvent {
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val functor: Functor
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val clauses: MutableList<Clause>
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/**
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* Creates a predicate with the given functor and an empty list of clauses.
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*/
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constructor(functor: Functor) {
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this.functor = functor
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this.clauses = mutableListOf()
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}
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/**
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* Creates a predicate with the given clauses.
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*/
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constructor(clauses: List<Clause>) {
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this.functor = clauses.first().functor
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require(clauses.all { it.functor == functor }) { "All clauses must have the same functor" }
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this.clauses = clauses.toMutableList()
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}
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/**
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* Adds a clause to the predicate.
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*/
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fun add(clause: Clause) {
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require(clause.functor == functor) { "Clause functor does not match predicate functor" }
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clauses.add(clause)
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}
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/**
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* Adds a list of clauses to the predicate.
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*/
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fun addAll(clauses: List<Clause>) {
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require(clauses.all { it.functor == functor }) { "All clauses must have the same functor" }
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this.clauses.addAll(clauses)
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}
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override fun solve(goal: Goal, subs: Substitutions): Answers = sequence {
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require(goal.functor == functor) { "Goal functor does not match predicate functor" }
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// Try to unify the goal with the clause
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// If the unification is successful, yield the substitutions
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clauses.forEach { yieldAll(it.solve(goal, subs)) }
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}
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}
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