src/theory/output_channel.h

   1 /*********************                                                        */
   2 /*! \file output_channel.h
   3  ** \verbatim
   4  ** Top contributors (to current version):
   5  **   Morgan Deters, Tim King, Liana Hadarean
   6  ** This file is part of the CVC4 project.
   7  ** Copyright (c) 2009-2019 by the authors listed in the file AUTHORS
   8  ** in the top-level source directory) and their institutional affiliations.
   9  ** All rights reserved.  See the file COPYING in the top-level source
  10  ** directory for licensing information.\endverbatim
  11  **
  12  ** \brief The theory output channel interface
  13  **
  14  ** The theory output channel interface.
  15  **/
  16
  17 #include "cvc4_private.h"
  18
  19 #ifndef CVC4__THEORY__OUTPUT_CHANNEL_H
  20 #define CVC4__THEORY__OUTPUT_CHANNEL_H
  21
  22 #include <memory>
  23
  24 #include "proof/proof_manager.h"
  25 #include "smt/logic_exception.h"
  26 #include "theory/interrupted.h"
  27 #include "util/proof.h"
  28 #include "util/resource_manager.h"
  29
  30 namespace CVC4 {
  31 namespace theory {
  32
  33 class Theory;
  34
  35 /**
  36  * A LemmaStatus, returned from OutputChannel::lemma(), provides information
  37  * about the lemma added.  In particular, it contains the T-rewritten lemma
  38  * for inspection and the user-level at which the lemma will reside.
  39  */
  40 class LemmaStatus {
  41  public:
  42   LemmaStatus(TNode rewrittenLemma, unsigned level)
  43       : d_rewrittenLemma(rewrittenLemma), d_level(level) {}
  44
  45   /** Get the T-rewritten form of the lemma. */
  46   TNode getRewrittenLemma() const { return d_rewrittenLemma; }
  47   /**
  48    * Get the user-level at which the lemma resides.  After this user level
  49    * is popped, the lemma is un-asserted from the SAT layer.  This level
  50    * will be 0 if the lemma didn't reach the SAT layer at all.
  51    */
  52   unsigned getLevel() const { return d_level; }
  53  private:
  54   Node d_rewrittenLemma;
  55   unsigned d_level;
  56 }; /* class LemmaStatus */
  57
  58 /**
  59  * Generic "theory output channel" interface.
  60  *
  61  * All methods can throw unrecoverable CVC4::Exception's unless otherwise
  62  * documented.
  63  */
  64 class OutputChannel {
  65  public:
  66   /** Construct an OutputChannel. */
  67   OutputChannel() {}
  68
  69   /**
  70    * Destructs an OutputChannel.  This implementation does nothing,
  71    * but we need a virtual destructor for safety in case subclasses
  72    * have a destructor.
  73    */
  74   virtual ~OutputChannel() {}
  75
  76   OutputChannel(const OutputChannel&) = delete;
  77   OutputChannel& operator=(const OutputChannel&) = delete;
  78
  79   /**
  80    * With safePoint(), the theory signals that it is at a safe point
  81    * and can be interrupted.
  82    *
  83    * @throws Interrupted if the theory can be safely interrupted.
  84    */
  85   virtual void safePoint(uint64_t amount) {}
  86
  87   /**
  88    * Indicate a theory conflict has arisen.
  89    *
  90    * @param n - a conflict at the current decision level.  This should
  91    * be an AND-kinded node of literals that are TRUE in the current
  92    * assignment and are in conflict (i.e., at least one must be
  93    * assigned false), or else a literal by itself (in the case of a
  94    * unit conflict) which is assigned TRUE (and T-conflicting) in the
  95    * current assignment.
  96    * @param pf - a proof of the conflict. This is only non-null if proofs
  97    * are enabled.
  98    */
  99   virtual void conflict(TNode n, std::unique_ptr<Proof> pf = nullptr) = 0;
 100
 101   /**
 102    * Propagate a theory literal.
 103    *
 104    * @param n - a theory consequence at the current decision level
 105    * @return false if an immediate conflict was encountered
 106    */
 107   virtual bool propagate(TNode n) = 0;
 108
 109   /**
 110    * Tell the core that a valid theory lemma at decision level 0 has
 111    * been detected.  (This requests a split.)
 112    *
 113    * @param n - a theory lemma valid at decision level 0
 114    * @param rule - the proof rule for this lemma
 115    * @param removable - whether the lemma can be removed at any point
 116    * @param preprocess - whether to apply more aggressive preprocessing
 117    * @param sendAtoms - whether to ensure atoms are sent to the theory
 118    * @return the "status" of the lemma, including user level at which
 119    * the lemma resides; the lemma will be removed when this user level pops
 120    */
 121   virtual LemmaStatus lemma(TNode n, ProofRule rule, bool removable = false,
 122                             bool preprocess = false,
 123                             bool sendAtoms = false) = 0;
 124
 125   /**
 126    * Variant of the lemma function that does not require providing a proof rule.
 127    */
 128   virtual LemmaStatus lemma(TNode n, bool removable = false,
 129                             bool preprocess = false, bool sendAtoms = false) {
 130     return lemma(n, RULE_INVALID, removable, preprocess, sendAtoms);
 131   }
 132
 133   /**
 134    * Request a split on a new theory atom.  This is equivalent to
 135    * calling lemma({OR n (NOT n)}).
 136    *
 137    * @param n - a theory atom; must be of Boolean type
 138    */
 139   LemmaStatus split(TNode n) { return splitLemma(n.orNode(n.notNode())); }
 140
 141   virtual LemmaStatus splitLemma(TNode n, bool removable = false) = 0;
 142
 143   /**
 144    * If a decision is made on n, it must be in the phase specified.
 145    * Note that this is enforced *globally*, i.e., it is completely
 146    * context-INdependent.  If you ever requirePhase() on a literal,
 147    * it is phase-locked forever and ever.  If it is to ever have the
 148    * other phase as its assignment, it will be because it has been
 149    * propagated that way (or it's a unit, at decision level 0).
 150    *
 151    * @param n - a theory atom with a SAT literal assigned; must have
 152    * been pre-registered
 153    * @param phase - the phase to decide on n
 154    */
 155   virtual void requirePhase(TNode n, bool phase) = 0;
 156
 157   /**
 158    * Notification from a theory that it realizes it is incomplete at
 159    * this context level.  If SAT is later determined by the
 160    * TheoryEngine, it should actually return an UNKNOWN result.
 161    */
 162   virtual void setIncomplete() = 0;
 163
 164   /**
 165    * "Spend" a "resource."  The meaning is specific to the context in
 166    * which the theory is operating, and may even be ignored.  The
 167    * intended meaning is that if the user has set a limit on the "units
 168    * of resource" that can be expended in a search, and that limit is
 169    * exceeded, then the search is terminated.  Note that the check for
 170    * termination occurs in the main search loop, so while theories
 171    * should call OutputChannel::spendResource() during particularly
 172    * long-running operations, they cannot rely on resource() to break
 173    * out of infinite or intractable computations.
 174    */
 175   virtual void spendResource(unsigned amount) {}
 176
 177   /**
 178    * Handle user attribute.
 179    * Associates theory t with the attribute attr.  Theory t will be
 180    * notified whenever an attribute of name attr is set on a node.
 181    * This can happen through, for example, the SMT-LIBv2 language.
 182    */
 183   virtual void handleUserAttribute(const char* attr, Theory* t) {}
 184
 185   /** Demands that the search restart from sat search level 0.
 186    * Using this leads to non-termination issues.
 187    * It is appropriate for prototyping for theories.
 188    */
 189   virtual void demandRestart() {}
 190
 191 }; /* class OutputChannel */
 192
 193 }  // namespace theory
 194 }  // namespace CVC4
 195
 196 #endif /* CVC4__THEORY__OUTPUT_CHANNEL_H */