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Experimental, functional-programming-based implementation of Prolog's SLDNF resolution principle
package it.unibo.tuprolog.solve.streams.solver
import it.unibo.tuprolog.core.Term
import it.unibo.tuprolog.solve.primitive.Solve
import it.unibo.tuprolog.solve.sideffects.SideEffectManager
import it.unibo.tuprolog.solve.streams.StreamsSolver
import it.unibo.tuprolog.solve.streams.stdlib.primitive.Call
import it.unibo.tuprolog.solve.streams.stdlib.primitive.Catch
import it.unibo.tuprolog.solve.streams.stdlib.primitive.Cut
import it.unibo.tuprolog.unify.Unificator.Companion.matches
/**
* Specific implementation of [SideEffectManager] for [StreamsSolver]
*
* @author Enrico
*/
internal data class SideEffectManagerImpl(
// CUT side effect fields
/** The sequence of parent execution contexts before this, limited to a "clause scope" */
private val clauseScopedParents: List = emptyList(),
/** Valued when this execution context is child of a choicePoint context, indicating a point where to cut */
private val isChoicePointChild: Boolean = false,
/** Filled when cut execution happens, this indicates which are the parent contexts whose unexplored children should be cut */
private val toCutContextsParent: Sequence = emptySequence(),
// Catch / Throw side effects fields
/** The sequence of parent [Solve.Request]s from this execution context till the resolution root */
internal val logicalParentRequests: List> = emptyList(),
/** The sequence of no more selectable parent requests, because already used */
private val throwNonSelectableParentContexts: Sequence = emptySequence(),
/** The execution context where a `catch` was found and till which other unexplored sub-trees should be cut */
private val throwRelatedToCutContextsParent: StreamsExecutionContext? = null
) : SideEffectManager {
override fun cut(): SideEffectManager = copy(
toCutContextsParent = toCutContextsParent + getFirstChoicePointContext() // only second value could be enough, but more testing needed
)
/** Initializes isChoicePointChild to `false` whatever it was, and adds given [currentContext] to clauseScopedParents */
internal fun stateInitInitialize(currentContext: StreamsExecutionContext): SideEffectManagerImpl = copy(
clauseScopedParents = clauseScopedParents.toMutableList().apply { add(0, currentContext) },
isChoicePointChild = false
)
/**
* Method that updates internal structures when creating a new solve request
*
* @param currentContext the context current before new solve request creation
* @param isChoicePointChild whether this solve request is child of a ChoicePoint
* @param logicalParentRequest the Solve.Request to be considered logically the parent of this (to correctly implement `catch/throw` interaction)
*/
internal fun creatingNewRequest(
currentContext: StreamsExecutionContext,
isChoicePointChild: Boolean,
logicalParentRequest: Solve.Request
) = copy(
clauseScopedParents = clauseScopedParents.toMutableList().apply { add(0, currentContext) },
isChoicePointChild = isChoicePointChild,
logicalParentRequests = when (logicalParentRequest) {
in logicalParentRequests -> logicalParentRequests.dropWhile { it != logicalParentRequest }
else -> logicalParentRequests.toMutableList().apply { add(0, logicalParentRequest) }
}
)
/** Method that updates sideEffects manager to not consider parents older than current first, because entering new "rule-scope" */
internal fun enterRuleSubScope() = copy(
clauseScopedParents = listOf(clauseScopedParents.first())
)
/** Method that updates clauseScopedParent to include upper scope parents; this is needed to maintain Cut functionality through Response chain */
internal fun extendParentScopeWith(upperScopeSideEffectsManager: SideEffectManagerImpl) = copy(
clauseScopedParents = clauseScopedParents
.toMutableList()
.apply { addAll(upperScopeSideEffectsManager.clauseScopedParents) }
)
/**
* Method that queries if a Cut should be executed in StateRuleSelection
*
* A cut should execute:
* - if throw was called, and not already caught
* - if cut was called, and the first "scoped" choice point context is to be cut
*/
internal fun shouldCutExecuteInRuleSelection() =
clauseScopedParents.lastOrNull() in toCutContextsParent ||
shouldExecuteThrowCut()
/** A method to retrieve the first ancestor catch request that has its second argument that unifies with [toUnifyArgument] */
internal fun retrieveAncestorCatchRequest(toUnifyArgument: Term): Solve.Request? {
val ancestorCatchesRequests = logicalParentRequests.filter { it.signature == Catch.signature }
.filterNot { it.context in throwNonSelectableParentContexts } // exclude already used catch requests
return ancestorCatchesRequests.find { it.arguments[1].matches(toUnifyArgument) }
}
/** Method to set the catch request whose not explored children should be cut from search tree */
internal fun throwCut(ancestorCatchContext: StreamsExecutionContext) = copy(
throwRelatedToCutContextsParent = ancestorCatchContext
)
/** Method to query if provided context was that selected by [throwCut] invocation */
internal fun isSelectedThrowCatch(contextImpl: StreamsExecutionContext) =
throwRelatedToCutContextsParent == contextImpl
/** Method to remove catch request with that [contextImpl], ensuring that's no more selectable */
internal fun ensureNoMoreSelectableCatch(contextImpl: StreamsExecutionContext) = copy(
throwNonSelectableParentContexts = throwNonSelectableParentContexts + contextImpl
)
/**
* Utility method to reset [Cut] changed data structures to initial value before exiting [Call] scope
*
* That implements expected ISO behaviour, for which *call/1 is said to be opaque (or not transparent) to cut.*
*/
internal fun resetCutWorkChanges(toRecoverSituation: SideEffectManagerImpl) =
// opaque behaviour of call/1 w.r.t cut/0, results in cancellation of sub-goal work onto "cut"'s data structures
copy(toCutContextsParent = toRecoverSituation.toCutContextsParent)
/**
* Method to query if the throw Cut should execute; the throw cut can exit clause Scope, so it uses different data structures
*/
internal fun shouldExecuteThrowCut() =
logicalParentRequests.any { it.context == throwRelatedToCutContextsParent }
/** Internal function to retrieve the first choice point to be Cut, if present */
private fun getFirstChoicePointContext() = clauseScopedParents
.filter { it.sideEffectManager.isChoicePointChild }
.mapNotNull { it.sideEffectManager.clauseScopedParents.firstOrNull() }
}
/** Bridge method to reach [SideEffectManagerImpl.shouldCutExecuteInRuleSelection] homonym method from a [SideEffectManager] */
internal fun SideEffectManager?.shouldCutExecuteInRuleSelection(): Boolean =
(this as? SideEffectManagerImpl)?.shouldCutExecuteInRuleSelection() ?: false
/** Bridge method to reach [SideEffectManagerImpl.extendParentScopeWith] homonym method from a [SideEffectManager] */
internal fun SideEffectManager?.extendParentScopeWith(upperScopeSideEffectsManager: SideEffectManagerImpl): SideEffectManagerImpl? =
(this as? SideEffectManagerImpl)?.extendParentScopeWith(upperScopeSideEffectsManager)
/** Bridge method to reach [SideEffectManagerImpl.resetCutWorkChanges] homonym method from a [SideEffectManager] */
internal fun SideEffectManager?.resetCutWorkChanges(toRecoverSituation: SideEffectManagerImpl): SideEffectManagerImpl? =
(this as? SideEffectManagerImpl)?.resetCutWorkChanges(toRecoverSituation)
/** Bridge method to reach [SideEffectManagerImpl.isSelectedThrowCatch] homonym method from a [SideEffectManager] */
internal fun SideEffectManager?.isSelectedThrowCatch(context: StreamsExecutionContext): Boolean =
(this as? SideEffectManagerImpl)?.isSelectedThrowCatch(context) ?: false
/** Bridge method to reach [SideEffectManagerImpl.shouldExecuteThrowCut] homonym method from a [SideEffectManager] */
internal fun SideEffectManager?.shouldExecuteThrowCut(): Boolean =
(this as? SideEffectManagerImpl)?.shouldExecuteThrowCut() ?: false