commonMain.it.unibo.tuprolog.solve.classic.fsm.StateRuleExecution.kt Maven / Gradle / Ivy

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Stable, state-machine-based implementation of Prolog's SLDNF resolution principle

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package it.unibo.tuprolog.solve.classic.fsm

import it.unibo.tuprolog.core.Substitution
import it.unibo.tuprolog.core.prepareForExecution
import it.unibo.tuprolog.solve.classic.ClassicExecutionContext
import it.unibo.tuprolog.unify.Unificator.Companion.mguWith
import it.unibo.tuprolog.utils.Cursor

data class StateRuleExecution(override val context: ClassicExecutionContext) : AbstractState(context) {
    private val failureState: StateBacktracking
        get() = StateBacktracking(context.copy(rules = Cursor.empty(), step = nextStep()))

    override fun computeNext(): State {
        return when (val unifier = context.goals.current!! mguWith context.rules.current!!.head) {
            is Substitution.Unifier -> {
                val newSubstitution = (context.substitution + unifier) as Substitution.Unifier
                val subGoals = context.rules.current!!.prepareForExecution(newSubstitution).body[newSubstitution]

                StateGoalSelection(
                    context.copy(
                        goals = subGoals.toGoals(),
                        rules = Cursor.empty(),
                        substitution = newSubstitution,
                        step = nextStep()
                    )
                )
            }
            else -> failureState
        }
    }

    override fun clone(context: ClassicExecutionContext): StateRuleExecution = copy(context = context)
}