Represents the equivalent of Prolog's once(Pred). The aim is to remove any choicepoints produced by Pred. More...

#include <pred.hpp>

Inheritance diagram for pl_search::Once:

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Collaboration diagram for pl_search::Once:

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Public Member Functions
	Once (Trail *trail, PredPtr pred)
	Constructs a Once predicate with the given trail and predicate.

bool	call () override
	Calls the once predicate.

Public Member Functions inherited from pl_search::Pred
	Pred (Trail *trail)
	Default constructor.

PredPtr	get_continuation ()
	Gets the continuation of the predicate.

virtual void	set_continuation (PredPtr cont)
	Sets the continuation of the predicate.

PredPtr	last_pred ()
	Follows the continuation chain to the last predicate.

virtual void	call_init ()
	Initialize call.

bool	call_continuation ()
	Calls the continuation of the predicate - first call_init and then call.

virtual	~Pred ()=default
	Virtual destructor for proper cleanup.

virtual std::string	get_name ()
	For debugging.

Protected Attributes
PredPtr	pred

Protected Attributes inherited from pl_search::Pred
PredPtr	continuation
	The continuation of the predicate.

Trail *	trail
	Pointer to the trail for managing variable bindings.

Detailed Description

Represents the equivalent of Prolog's once(Pred). The aim is to remove any choicepoints produced by Pred.

The meta-predicate Once is used to remove any choicepoints produced by Pred. If Pred succeeds then the continuation is called and any choicepoints produced by Pred are removed. If Pred or the continuation fails then the Once predicate fails and any bindings produced by Pred are undone. Note that Pred is a local call - i.e. its continuation is not related to the continuation of the Once predicate. Also note that Pred could be a conjunction of predicates.

Constructor & Destructor Documentation

◆ Once()

pl_search::Once::Once	(	Trail *	trail,
		PredPtr	pred
	)

inline

Constructs a Once predicate with the given trail and predicate.

Parameters

trail	Pointer to the trail.
pred	The predicate called within the once.

Member Function Documentation

◆ call()

bool pl_search::Once::call ( )

overridevirtual

Calls the once predicate.

Returns: True if the predicate succeeds and the continuation succeeds, false otherwise, removing any choicepoints produced by the predicate.

When a Once object is called it calls the predicate supplied to the Once constructor. If the call fails then the Once predicate fails and any bindings created by the call are undone. If the call succeeds then the continuation is called. Note that no alternative choices for pred are tried if the continuation fails. The Once predicate is used to remove any choicepoints produced by pred.

Reimplemented from pl_search::Pred.

Member Data Documentation

◆ pred

PredPtr pl_search::Once::pred

protected

The documentation for this class was generated from the following files:

include/pl_search/pred.hpp
src/pred.cpp

Public Member Functions