src/theory/output_channel.h

   1 /*********************                                                        */
   2 /*! \file output_channel.h
   3  ** \verbatim
   4  ** Original author: Morgan Deters
   5  ** Major contributors: none
   6  ** Minor contributors (to current version): Andrew Reynolds, Dejan Jovanovic, Tim King
   7  ** This file is part of the CVC4 project.
   8  ** Copyright (c) 2009-2014  New York University and The University of Iowa
   9  ** See the file COPYING in the top-level source directory for licensing
  10  ** 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 "util/cvc4_assert.h"
  23 #include "theory/interrupted.h"
  24
  25 namespace CVC4 {
  26 namespace theory {
  27
  28 class Theory;
  29
  30 /**
  31  * A LemmaStatus, returned from OutputChannel::lemma(), provides information
  32  * about the lemma added.  In particular, it contains the T-rewritten lemma
  33  * for inspection and the user-level at which the lemma will reside.
  34  */
  35 class LemmaStatus {
  36   Node d_rewrittenLemma;
  37   unsigned d_level;
  38
  39 public:
  40   LemmaStatus(TNode rewrittenLemma, unsigned level) :
  41     d_rewrittenLemma(rewrittenLemma),
  42     d_level(level) {
  43   }
  44
  45   /** Get the T-rewritten form of the lemma. */
  46   TNode getRewrittenLemma() const throw() { return d_rewrittenLemma; }
  47
  48   /**
  49    * Get the user-level at which the lemma resides.  After this user level
  50    * is popped, the lemma is un-asserted from the SAT layer.  This level
  51    * will be 0 if the lemma didn't reach the SAT layer at all.
  52    */
  53   unsigned getLevel() const throw() { return d_level; }
  54
  55 };/* class LemmaStatus */
  56
  57 /**
  58  * Generic "theory output channel" interface.
  59  */
  60 class OutputChannel {
  61   /** Disallow copying: private constructor */
  62   OutputChannel(const OutputChannel&) CVC4_UNDEFINED;
  63
  64   /** Disallow assignment: private operator=() */
  65   OutputChannel& operator=(const OutputChannel&) CVC4_UNDEFINED;
  66
  67 public:
  68
  69   /**
  70    * Construct an OutputChannel.
  71    */
  72   OutputChannel() {
  73   }
  74
  75   /**
  76    * Destructs an OutputChannel.  This implementation does nothing,
  77    * but we need a virtual destructor for safety in case subclasses
  78    * have a destructor.
  79    */
  80   virtual ~OutputChannel() {
  81   }
  82
  83   /**
  84    * With safePoint(), the theory signals that it is at a safe point
  85    * and can be interrupted.
  86    */
  87   virtual void safePoint() throw(Interrupted, AssertionException) {
  88   }
  89
  90   /**
  91    * Indicate a theory conflict has arisen.
  92    *
  93    * @param n - a conflict at the current decision level.  This should
  94    * be an AND-kinded node of literals that are TRUE in the current
  95    * assignment and are in conflict (i.e., at least one must be
  96    * assigned false), or else a literal by itself (in the case of a
  97    * unit conflict) which is assigned TRUE (and T-conflicting) in the
  98    * current assignment.
  99    */
 100   virtual void conflict(TNode n) throw(AssertionException) = 0;
 101
 102   /**
 103    * Propagate a theory literal.
 104    *
 105    * @param n - a theory consequence at the current decision level
 106    * @return false if an immediate conflict was encountered
 107    */
 108   virtual bool propagate(TNode n) throw(AssertionException) = 0;
 109
 110   /**
 111    * Tell the core that a valid theory lemma at decision level 0 has
 112    * been detected.  (This requests a split.)
 113    *
 114    * @param n - a theory lemma valid at decision level 0
 115    * @param removable - whether the lemma can be removed at any point
 116    * @param preprocess - whether to apply more aggressive preprocessing
 117    * @return the "status" of the lemma, including user level at which
 118    * the lemma resides; the lemma will be removed when this user level pops
 119    */
 120   virtual LemmaStatus lemma(TNode n, bool removable = false,
 121                             bool preprocess = false)
 122     throw(TypeCheckingExceptionPrivate, AssertionException) = 0;
 123
 124   /**
 125    * Request a split on a new theory atom.  This is equivalent to
 126    * calling lemma({OR n (NOT n)}).
 127    *
 128    * @param n - a theory atom; must be of Boolean type
 129    */
 130   LemmaStatus split(TNode n)
 131     throw(TypeCheckingExceptionPrivate, AssertionException) {
 132     return splitLemma(n.orNode(n.notNode()));
 133   }
 134
 135   virtual LemmaStatus splitLemma(TNode n, bool removable = false)
 136     throw(TypeCheckingExceptionPrivate, AssertionException) = 0;
 137
 138   /**
 139    * If a decision is made on n, it must be in the phase specified.
 140    * Note that this is enforced *globally*, i.e., it is completely
 141    * context-INdependent.  If you ever requirePhase() on a literal,
 142    * it is phase-locked forever and ever.  If it is to ever have the
 143    * other phase as its assignment, it will be because it has been
 144    * propagated that way (or it's a unit, at decision level 0).
 145    *
 146    * @param n - a theory atom with a SAT literal assigned; must have
 147    * been pre-registered
 148    * @param phase - the phase to decide on n
 149    */
 150   virtual void requirePhase(TNode n, bool phase)
 151     throw(Interrupted, TypeCheckingExceptionPrivate, AssertionException) = 0;
 152
 153   /**
 154    * Flips the most recent unflipped decision to the other phase and
 155    * returns true.  If all decisions have been flipped, the root
 156    * decision is re-flipped and flipDecision() returns false.  If no
 157    * decisions (flipped nor unflipped) are on the decision stack, the
 158    * state is not affected and flipDecision() returns false.
 159    *
 160    * For example, if l1, l2, and l3 are all decision literals, and
 161    * have been decided in positive phase, a series of flipDecision()
 162    * calls has the following effects:
 163    *
 164    * l1 l2 l3 <br/>
 165    * l1 l2 ~l3 <br/>
 166    * l1 ~l2 <br/>
 167    * ~l1 <br/>
 168    * l1 (and flipDecision() returns false)
 169    *
 170    * Naturally, flipDecision() might be interleaved with search.  For example:
 171    *
 172    * l1 l2 l3 <br/>
 173    * flipDecision() <br/>
 174    * l1 l2 ~l3 <br/>
 175    * flipDecision() <br/>
 176    * l1 ~l2 <br/>
 177    * SAT decides l3 <br/>
 178    * l1 ~l2 l3 <br/>
 179    * flipDecision() <br/>
 180    * l1 ~l2 ~l3 <br/>
 181    * flipDecision() <br/>
 182    * ~l1 <br/>
 183    * SAT decides l2 <br/>
 184    * ~l1 l2 <br/>
 185    * flipDecision() <br/>
 186    * ~l1 ~l2 <br/>
 187    * flipDecision() returns FALSE<br/>
 188    * l1
 189    *
 190    * @return true if a decision was flipped; false if no decision
 191    * could be flipped, or if the root decision was re-flipped
 192    */
 193   virtual bool flipDecision()
 194     throw(Interrupted, TypeCheckingExceptionPrivate, AssertionException) = 0;
 195
 196   /**
 197    * Notification from a theory that it realizes it is incomplete at
 198    * this context level.  If SAT is later determined by the
 199    * TheoryEngine, it should actually return an UNKNOWN result.
 200    */
 201   virtual void setIncomplete() throw(AssertionException) = 0;
 202
 203   /**
 204    * "Spend" a "resource."  The meaning is specific to the context in
 205    * which the theory is operating, and may even be ignored.  The
 206    * intended meaning is that if the user has set a limit on the "units
 207    * of resource" that can be expended in a search, and that limit is
 208    * exceeded, then the search is terminated.  Note that the check for
 209    * termination occurs in the main search loop, so while theories
 210    * should call OutputChannel::spendResource() during particularly
 211    * long-running operations, they cannot rely on resource() to break
 212    * out of infinite or intractable computations.
 213    */
 214   virtual void spendResource() throw() {}
 215
 216   /**
 217    * Handle user attribute.
 218    * Associates theory t with the attribute attr.  Theory t will be
 219    * notified whenever an attribute of name attr is set on a node.
 220    * This can happen through, for example, the SMT-LIBv2 language.
 221    */
 222   virtual void handleUserAttribute(const char* attr, Theory* t) {}
 223
 224
 225   /** Demands that the search restart from sat search level 0.
 226    * Using this leads to non-termination issues.
 227    * It is appropriate for prototyping for theories.
 228    */
 229   virtual void demandRestart() throw(TypeCheckingExceptionPrivate, AssertionException) {}
 230
 231 };/* class OutputChannel */
 232
 233 }/* CVC4::theory namespace */
 234 }/* CVC4 namespace */
 235
 236 #endif /* __CVC4__THEORY__OUTPUT_CHANNEL_H */