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Experimental, functional-programming-based implementation of Prolog's SLDNF resolution principle

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package it.unibo.tuprolog.solve.streams.stdlib.primitive

import it.unibo.tuprolog.solve.exception.error.TypeError
import it.unibo.tuprolog.solve.primitive.PrimitiveWrapper
import it.unibo.tuprolog.solve.primitive.Solve
import it.unibo.tuprolog.solve.streams.StreamsSolver
import it.unibo.tuprolog.solve.streams.solver.StreamsExecutionContext
import it.unibo.tuprolog.solve.streams.solver.isWellFormed
import it.unibo.tuprolog.solve.streams.solver.newSolveRequest
import it.unibo.tuprolog.solve.streams.solver.prepareForExecutionAsGoal
import it.unibo.tuprolog.solve.streams.solver.replyWith
import it.unibo.tuprolog.solve.streams.solver.resetCutWorkChanges

/**
 * Implementation of primitive handling `call/1` behaviour
 *
 * @author Enrico
 */
internal object Call : PrimitiveWrapper("call", 1) {

    override fun uncheckedImplementation(request: Solve.Request): Sequence =
        request.ensuringAllArgumentsAreInstantiated().arguments.single().let { toBeCalledGoal ->
            when {
                toBeCalledGoal.isWellFormed() ->
                    StreamsSolver.solveToResponses(request.newSolveRequest(toBeCalledGoal.prepareForExecutionAsGoal())).map {
                        request.replyWith(
                            it.copy(
                                sideEffectManager = it.sideEffectManager
                                    .resetCutWorkChanges(request.context.sideEffectManager)
                            )
                        )
                    }

                else -> throw TypeError(
                    message = "call/1 argument is neither a Variable nor a well-formed goal",
                    context = request.context,
                    expectedType = TypeError.Expected.CALLABLE,
                    culprit = toBeCalledGoal
                )
            }
        }
}