path: root/src/theory/theory_model_builder.h

/******************************************************************************
 * Top contributors (to current version):
 *   Andrew Reynolds, Mathias Preiner, Tim King
 *
 * This file is part of the cvc5 project.
 *
 * Copyright (c) 2009-2021 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.
 * ****************************************************************************
 *
 * Model class.
 */

#include "cvc5_private.h"

#ifndef CVC5__THEORY__THEORY_MODEL_BUILDER_H
#define CVC5__THEORY__THEORY_MODEL_BUILDER_H

#include <unordered_map>
#include <unordered_set>

#include "smt/env_obj.h"
#include "theory/theory_model.h"

namespace cvc5 {

class Env;

namespace theory {

/** TheoryEngineModelBuilder class
 *
 * This is the class used by TheoryEngine
 * for constructing TheoryModel objects, which is the class
 * that represents models for a set of assertions.
 *
 * A call to TheoryEngineModelBuilder::buildModel(...) is made
 * after a full effort check passes with no theory solvers
 * adding lemmas or conflicts, and theory combination passes
 * with no splits on shared terms. If buildModel is successful,
 * this will set up the data structures in TheoryModel to represent
 * a model for the current set of assertions.
 */
class TheoryEngineModelBuilder : protected EnvObj
{
  typedef std::unordered_map<Node, Node> NodeMap;
  typedef std::unordered_set<Node> NodeSet;

 public:
  TheoryEngineModelBuilder(Env& env);
  virtual ~TheoryEngineModelBuilder() {}
  /**
   * Should be called only on models m after they have been prepared
   * (e.g. using ModelManager). In other words, the equality engine of model
   * m contains all relevant information from each theory that is needed
   * for building a model. This class is responsible simply for ensuring
   * that all equivalence classes of the equality engine of m are assigned
   * constants.
   *
   * This constructs the model m, via the following steps:
   * (1) builder-specified pre-processing,
   * (2) find the equivalence classes of m's
   *     equality engine that initially contain constants,
   * (3) assign constants to all equivalence classes
   *     of m's equality engine, through alternating
   *     iterations of evaluation and enumeration,
   * (4) builder-specific processing, which includes assigning total
   *     interpretations to uninterpreted functions.
   *
   * This function returns false if any of the above
   * steps results in a lemma sent on an output channel.
   * Lemmas may be sent on an output channel by this
   * builder in steps (2) or (5), for instance, if the model we
   * are building fails to satisfy a quantified formula.
   *
   * @param m The model to build
   * @return true if the model was successfully built.
   */
  bool buildModel(TheoryModel* m);

  /** postprocess model
   *
   * This is called when m is a model that will be returned to the user. This
   * method checks the internal consistency of the model if we are in a debug
   * build.
   */
  void postProcessModel(bool incomplete, TheoryModel* m);

 protected:

  //-----------------------------------virtual functions
  /** pre-process build model
   * Do pre-processing specific to this model builder.
   * Called in step (2) of the build construction,
   * described above.
   */
  virtual bool preProcessBuildModel(TheoryModel* m);
  /** process build model
   * Do processing specific to this model builder.
   * Called in step (5) of the build construction,
   * described above.
   * By default, this assigns values to each function
   * that appears in m's equality engine.
   */
  virtual bool processBuildModel(TheoryModel* m);
  /** debug the model
   * Check assertions and printing debug information for the model.
   * Calls after step (5) described above is complete.
   */
  virtual void debugModel(TheoryModel* m) {}
  //-----------------------------------end virtual functions

  /** Debug check model.
   *
   * This throws an assertion failure if the model contains an equivalence
   * class with two terms t1 and t2 such that t1^M != t2^M.
   */
  void debugCheckModel(TheoryModel* m);

  /** Evaluate equivalence class
   *
   * If this method returns a non-null node c, then c is a constant and some
   * term in the equivalence class of r evaluates to c based on the current
   * state of the model m.
   */
  Node evaluateEqc(TheoryModel* m, TNode r);
  /** is n an assignable expression?
   *
   * A term n is an assignable expression if its value is unconstrained by a
   * standard model. Examples of assignable terms are:
   * - variables,
   * - applications of array select,
   * - applications of datatype selectors,
   * - applications of uninterpreted functions.
   * Assignable terms must be first-order, that is, all instances of the above
   * terms are not assignable if they have a higher-order (function) type.
   */
  bool isAssignable(TNode n);
  /** add assignable subterms
   * Adds all assignable subterms of n to tm's equality engine.
   */
  void addAssignableSubterms(TNode n, TheoryModel* tm, NodeSet& cache);
  /** normalize representative r
   *
   * This returns a term that is equivalent to r's
   * interpretation in the model m. It may do so
   * by rewriting the application of r's operator to the
   * result of normalizing each of r's children, if
   * each child is constant.
   */
  Node normalize(TheoryModel* m, TNode r, bool evalOnly);
  /** assign constant representative
   *
   * Called when equivalence class eqc is assigned a constant
   * representative const_rep.
   *
   * eqc should be a representative of tm's equality engine.
   */
  void assignConstantRep(TheoryModel* tm, Node eqc, Node const_rep);
  /** add to type list
   *
   * This adds to type_list the list of types that tn is built from.
   * For example, if tn is (Array Int Bool) and type_list is empty,
   * then we append ( Int, Bool, (Array Int Bool) ) to type_list.
   */
  void addToTypeList(TypeNode tn,
                     std::vector<TypeNode>& type_list,
                     std::unordered_set<TypeNode>& visiting);
  /** assign function f based on the model m.
  * This construction is based on "table form". For example:
  * (f 0 1) = 1
  * (f 0 2) = 2
  * (f 1 1) = 3
  * ...
  * becomes:
  * f = (lambda xy. (ite (and (= x 0) (= y 1)) 1
  *                 (ite (and (= x 0) (= y 2)) 2
  *                 (ite (and (= x 1) (= y 1)) 3 ...)))
  */
  void assignFunction(TheoryModel* m, Node f);
  /** assign function f based on the model m.
  * This construction is based on "dag form". For example:
  * (f 0 1) = 1
  * (f 0 2) = 2
  * (f 1 1) = 3
  * ...
  * becomes:
  * f = (lambda xy. (ite (= x 0) (ite (= y 1) 1
  *                              (ite (= y 2) 2 ...))
  *                 (ite (= x 1) (ite (= y 1) 3 ...)
  *                              ...))
  *
  * where the above is represented as a directed acyclic graph (dag).
  * This construction is accomplished by assigning values to (f c)
  * terms before f, e.g.
  * (f 0) = (lambda y. (ite (= y 1) 1
  *                    (ite (= y 2) 2 ...))
  * (f 1) = (lambda y. (ite (= y 1) 3 ...))
  * where
  * f = (lambda xy. (ite (= x 0) ((f 0) y)
  *                 (ite (= x 1) ((f 1) y) ...))
  */
  void assignHoFunction(TheoryModel* m, Node f);
  /** assign functions
   *
   * Assign all unassigned functions in the model m (those returned by
   * TheoryModel::getFunctionsToAssign),
   * using the two functions above. Currently:
   * If HO logic is disabled, we call assignFunction for all functions.
   * If HO logic is enabled, we call assignHoFunction.
   */
  void assignFunctions(TheoryModel* m);

 private:
  /** normalized cache
   * A temporary cache mapping terms to their
   * normalized form, used during buildModel.
   */
  NodeMap d_normalizedCache;
  /** mapping from terms to the constant associated with their equivalence class
   */
  std::map<Node, Node> d_constantReps;

  /** Theory engine model builder assigner class
   *
   * This manages the assignment of values to terms of a given type.
   * In particular, it is a wrapper around a type enumerator that is restricted
   * by a set of values that it cannot generate, called an "assignment exclusion
   * set".
   */
  class Assigner
  {
   public:
    Assigner() : d_te(nullptr), d_isActive(false) {}
    /**
     * Initialize this assigner to generate values of type tn, with properties
     * tep and assignment exclusion set aes.
     */
    void initialize(TypeNode tn,
                    TypeEnumeratorProperties* tep,
                    const std::vector<Node>& aes);
    /** get the next term in the enumeration
     *
     * This method returns the next legal term based on type enumeration, where
     * a term is legal it does not belong to the assignment exclusion set of
     * this assigner. If no more terms exist, this method returns null. This
     * should never be the case due to the conditions ensured by theory solvers
     * for finite types. If it is the case, we give an assertion failure.
     */
    Node getNextAssignment();
    /** The type enumerator */
    std::unique_ptr<TypeEnumerator> d_te;
    /** The assignment exclusion set of this Assigner */
    std::vector<Node> d_assignExcSet;
    /**
     * Is active, flag set to true when all values in d_assignExcSet are
     * constant.
     */
    bool d_isActive;
  };
  /** Is the given Assigner ready to assign values?
   *
   * This returns true if all values in the assignment exclusion set of a have
   * a known value according to the state of this model builder (via a lookup
   * in d_constantReps). It updates the assignment exclusion vector of a to
   * these values whenever possible.
   */
  bool isAssignerActive(TheoryModel* tm, Assigner& a);
  //------------------------------------for codatatypes
  /** is v an excluded codatatype value?
   *
   * If this returns true, then v is a value
   * that cannot be used during enumeration in step (4)
   * of model construction.
   *
   * repSet is the set of representatives of the same type as v,
   * assertedReps is a map from representatives t,
   * eqc is the equivalence class that v reside.
   *
   * This function is used to avoid alpha-equivalent
   * assignments for codatatype terms, described in
   * Reynolds/Blanchette CADE 2015. In particular,
   * this function returns true if v is in
   * the set V^{x}_I from page 9, where x is eqc
   * and I is the model we are building.
   */
  bool isExcludedCdtValue(Node v,
                          std::set<Node>* repSet,
                          std::map<Node, Node>& assertedReps,
                          Node eqc);
  /** is codatatype value match
   *
   * This returns true if v is r{ eqc -> t } for some t.
   * If this function returns true, then t above is
   * stored in eqc_m.
   */
  bool isCdtValueMatch(Node v, Node r, Node eqc, Node& eqc_m);
  //------------------------------------end for codatatypes

  //---------------------------------for debugging finite model finding
  /** does type tn involve an uninterpreted sort? */
  bool involvesUSort(TypeNode tn) const;
  /** is v an excluded value based on uninterpreted sorts?
   * This gives an assertion failure in the case that v contains
   * an uninterpreted constant whose index is out of the bounds
   * specified by eqc_usort_count.
   */
  bool isExcludedUSortValue(std::map<TypeNode, unsigned>& eqc_usort_count,
                            Node v,
                            std::map<Node, bool>& visited);
  //---------------------------------end for debugging finite model finding
}; /* class TheoryEngineModelBuilder */

}  // namespace theory
}  // namespace cvc5

#endif /* CVC5__THEORY__THEORY_MODEL_BUILDER_H */