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/********************* */
/*! \file sygus_pbe.h
** \verbatim
** Top contributors (to current version):
** Andrew Reynolds, Haniel Barbosa
** This file is part of the CVC4 project.
** Copyright (c) 2009-2019 by the authors listed in the file AUTHORS
** in the top-level source directory) and their institutional affiliations.
** All rights reserved. See the file COPYING in the top-level source
** directory for licensing information.\endverbatim
**
** \brief utility for processing programming by examples synthesis conjectures
**/
#include "cvc4_private.h"
#ifndef CVC4__THEORY__QUANTIFIERS__SYGUS_PBE_H
#define CVC4__THEORY__QUANTIFIERS__SYGUS_PBE_H
#include "context/cdhashmap.h"
#include "theory/quantifiers/sygus/sygus_module.h"
#include "theory/quantifiers/sygus/sygus_unif_io.h"
namespace CVC4 {
namespace theory {
namespace quantifiers {
class SynthConjecture;
/** SygusPbe
*
* This class implements optimizations that target synthesis conjectures
* that are in Programming-By-Examples (PBE) form.
*
* [EX#1] An example of a synthesis conjecture in PBE form is :
* exists f. forall x.
* ( f( 0 ) = 2 ) ^ ( f( 5 ) = 7 ) ^ ( f( 6 ) = 8 )
*
* We say that the above conjecture has I/O examples (0)->2, (5)->7, (6)->8.
*
* Internally, this class does the following for SyGuS inputs:
*
* (1) Infers whether the input conjecture is in PBE form or not, which
* is based on looking up information in the ExampleInfer utility.
* (2) Based on this information and on the syntactic restrictions, it
* devises a strategy for enumerating terms and construction solutions,
* which is inspired by Alur et al. "Scaling Enumerative Program Synthesis
* via Divide and Conquer" TACAS 2017. In particular, it may consider
* strategies for constructing decision trees when the grammar permits ITEs
* and a strategy for divide-and-conquer string synthesis when the grammar
* permits string concatenation. This is managed through the SygusUnif
* utilities, d_sygus_unif.
* (3) It makes (possibly multiple) calls to
* TermDatabaseSygus::regstierEnumerator(...) based
* on the strategy, which inform the rest of the system to enumerate values
* of particular types in the grammar through use of fresh variables which
* we call "enumerators".
*
* Points (1)-(3) happen within a call to SygusPbe::initialize(...).
*
* Notice that each enumerator is associated with a single
* function-to-synthesize, but a function-to-sythesize may be mapped to multiple
* enumerators. Some public functions of this class expect an enumerator as
* input, which we map to a function-to-synthesize via
* TermDatabaseSygus::getSynthFunFor(e).
*
* An enumerator is initially "active" but may become inactive if the
* enumeration exhausts all possible values in the datatype corresponding to
* syntactic restrictions for it. The search may continue unless all enumerators
* become inactive.
*
* (4) When the extension of quantifier-free datatypes procedure for SyGuS
* datatypes terminates with a model, the parent of this class calls
* SygusPbe::getCandidateList(...), where this class returns the list
* of active enumerators.
* (5) The parent class subsequently calls
* SygusPbe::constructValues(...), which informs this class that new
* values have been enumerated for active enumerators, as indicated by the
* current model. This call also requests that based on these
* newly enumerated values, whether this class is now able to construct a
* solution based on the high-level strategy (stored in d_sygus_unif).
*
* This class is not designed to work in incremental mode, since there is no way
* to specify incremental problems in SyguS.
*/
class SygusPbe : public SygusModule
{
public:
SygusPbe(QuantifiersEngine* qe, SynthConjecture* p);
~SygusPbe();
/** initialize this class
*
* This function may add lemmas to the vector lemmas corresponding
* to initial lemmas regarding static analysis of enumerators it
* introduced. For example, we may say that the top-level symbol
* of an enumerator is not ITE if it is being used to construct
* return values for decision trees.
*/
bool initialize(Node conj,
Node n,
const std::vector<Node>& candidates,
std::vector<Node>& lemmas) override;
/** get term list
*
* Adds all active enumerators associated with functions-to-synthesize in
* candidates to terms.
*/
void getTermList(const std::vector<Node>& candidates,
std::vector<Node>& terms) override;
/**
* PBE allows partial models to handle multiple enumerators if we are not
* using a strictly fair enumeration strategy.
*/
bool allowPartialModel() override;
/** construct candidates
*
* This function attempts to use unification-based approaches for constructing
* solutions for all functions-to-synthesize (indicated by candidates). These
* approaches include decision tree learning and a divide-and-conquer
* algorithm based on string concatenation.
*
* Calls to this function are such that terms is the list of active
* enumerators (returned by getTermList), and term_values are their current
* model values. This function registers { terms -> terms_values } in
* the database of values that have been enumerated, which are in turn used
* for constructing candidate solutions when possible.
*
* This function also excludes models where (terms = terms_values) by adding
* blocking clauses to lems. For example, for grammar:
* A -> A+A | x | 1 | 0
* and a call where terms = { d } and term_values = { +( x, 1 ) }, it adds:
* ~G V ~is_+( d ) V ~is_x( d.1 ) V ~is_1( d.2 )
* to lems, where G is active guard of the enumerator d (see
* TermDatabaseSygus::getActiveGuardForEnumerator). This blocking clause
* indicates that d should not be given the model value +( x, 1 ) anymore,
* since { d -> +( x, 1 ) } has now been added to the database of this class.
*/
bool constructCandidates(const std::vector<Node>& terms,
const std::vector<Node>& term_values,
const std::vector<Node>& candidates,
std::vector<Node>& candidate_values,
std::vector<Node>& lems) override;
/** is PBE enabled for any enumerator? */
bool isPbe() { return d_is_pbe; }
private:
/** true and false nodes */
Node d_true;
Node d_false;
/** is this a PBE conjecture for any function? */
bool d_is_pbe;
/**
* Map from candidates to sygus unif utility. This class implements
* the core algorithm (e.g. decision tree learning) that this module relies
* upon.
*/
std::map<Node, std::unique_ptr<SygusUnifIo> > d_sygus_unif;
/**
* map from candidates to the list of enumerators that are being used to
* build solutions for that candidate by the above utility.
*/
std::map<Node, std::vector<Node> > d_candidate_to_enum;
/** reverse map of above */
std::map<Node, Node> d_enum_to_candidate;
};
} /* namespace CVC4::theory::quantifiers */
} /* namespace CVC4::theory */
} /* namespace CVC4 */
#endif
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