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

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

There is a newer version: 1.0.4

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

import it.unibo.tuprolog.solve.Solution
import it.unibo.tuprolog.solve.classic.ClassicExecutionContext

data class StateBacktracking(override val context: ClassicExecutionContext) : AbstractState(context) {
    override fun computeNext(): State {
        val choicePoints = context.choicePoints
        return if (choicePoints.let { it === null || !it.hasOpenAlternatives }) {
            StateEnd(
                solution = Solution.no(context.query),
                context = context.copy(step = nextStep()),
            )
        } else {
            val choicePointContext = choicePoints!!.pathToRoot.first { it.alternatives.hasNext }
            val nextContext = choicePointContext.backtrack(context)
            if (nextContext.primitives.hasNext) {
                StatePrimitiveExecution(nextContext)
            } else {
                StateRuleExecution(nextContext)
            }
        }
    }

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