internal override BoolExpr <T_Identifier> VisitNot(NotExpr <T_Identifier> expression)
{
BoolExpr <T_Identifier> child = expression.Child.Accept(this);
switch (child.ExprType)
{
case ExprType.Not:
return(((NotExpr <T_Identifier>)child).Child);
case ExprType.True: return(FalseExpr <T_Identifier> .Value);
case ExprType.False: return(TrueExpr <T_Identifier> .Value);
default: return(base.VisitNot(expression));
}
}
/// <summary>
/// Initialize a new Not expression with the given child.
/// </summary>
/// <param name="child"></param>
internal NotExpr(BoolExpr <T_Identifier> child)
: base(new BoolExpr <T_Identifier>[] { child })
{
}
protected override bool EquivalentTypeEquals(BoolExpr <T_Identifier> other)
{
return(((TreeExpr <T_Identifier>)other).Children.SetEquals(Children));
}
protected override bool EquivalentTypeEquals(BoolExpr <T_Identifier> other)
{
return(_comparer.Equals(_identifier, ((TermExpr <T_Identifier>)other)._identifier));
}
protected override bool EquivalentTypeEquals(BoolExpr <T_Identifier> other)
{
return(object.ReferenceEquals(this, other));
}
protected abstract bool EquivalentTypeEquals(BoolExpr <T_Identifier> other);
// (left iff. right) iff. (left --> right AND right --> left)
internal Equivalence(BoolExpr <T_Identifier> left, BoolExpr <T_Identifier> right)
: base(new Implication(left, right), new Implication(right, left))
{
_left = left;
_right = right;
}
private BoolExpr <T_Identifier> SimplifyTree(TreeExpr <T_Identifier> tree)
{
bool isAnd = ExprType.And == tree.ExprType;
Debug.Assert(isAnd || ExprType.Or == tree.ExprType);
// Get list of simplified children, flattening nested And/Or expressions
List <BoolExpr <T_Identifier> > simplifiedChildren = new List <BoolExpr <T_Identifier> >(tree.Children.Count);
foreach (BoolExpr <T_Identifier> child in tree.Children)
{
BoolExpr <T_Identifier> simplifiedChild = child.Accept(this);
// And(And(A, B), C) iff. And(A, B, C)
// Or(Or(A, B), C) iff. Or(A, B, C)
if (simplifiedChild.ExprType == tree.ExprType)
{
simplifiedChildren.AddRange(((TreeExpr <T_Identifier>)simplifiedChild).Children);
}
else
{
simplifiedChildren.Add(simplifiedChild);
}
}
// Track negated children separately to identify tautologies and contradictions
Dictionary <BoolExpr <T_Identifier>, bool> negatedChildren = new Dictionary <BoolExpr <T_Identifier>, bool>(tree.Children.Count);
List <BoolExpr <T_Identifier> > otherChildren = new List <BoolExpr <T_Identifier> >(tree.Children.Count);
foreach (BoolExpr <T_Identifier> simplifiedChild in simplifiedChildren)
{
switch (simplifiedChild.ExprType)
{
case ExprType.Not:
negatedChildren[((NotExpr <T_Identifier>)simplifiedChild).Child] = true;
break;
case ExprType.False:
// False And A --> False
if (isAnd)
{
return(FalseExpr <T_Identifier> .Value);
}
// False || A --> A (omit False from child collections)
break;
case ExprType.True:
// True Or A --> True
if (!isAnd)
{
return(TrueExpr <T_Identifier> .Value);
}
// True And A --> A (omit True from child collections)
break;
default:
otherChildren.Add(simplifiedChild);
break;
}
}
List <BoolExpr <T_Identifier> > children = new List <BoolExpr <T_Identifier> >();
foreach (BoolExpr <T_Identifier> child in otherChildren)
{
if (negatedChildren.ContainsKey(child))
{
// A && !A --> False, A || !A --> True
if (isAnd)
{
return(FalseExpr <T_Identifier> .Value);
}
else
{
return(TrueExpr <T_Identifier> .Value);
}
}
children.Add(child);
}
foreach (BoolExpr <T_Identifier> child in negatedChildren.Keys)
{
children.Add(child.MakeNegated());
}
if (0 == children.Count)
{
// And() iff. True
if (isAnd)
{
return(TrueExpr <T_Identifier> .Value);
}
// Or() iff. False
else
{
return(FalseExpr <T_Identifier> .Value);
}
}
else if (1 == children.Count)
{
// Or(A) iff. A, And(A) iff. A
return(children[0]);
}
else
{
// Construct simplified And/Or expression
TreeExpr <T_Identifier> result;
if (isAnd)
{
result = new AndExpr <T_Identifier>(children);
}
else
{
result = new OrExpr <T_Identifier>(children);
}
return(result);
}
}
internal static IEnumerable <T_Identifier> GetLeaves(BoolExpr <T_Identifier> expression)
{
return(GetTerms(expression).Select(term => term.Identifier));
}
internal static BoolExpr <DomainConstraint <T_Variable, T_Element> > EliminateNot <T_Variable, T_Element>(BoolExpr <DomainConstraint <T_Variable, T_Element> > expression)
{
return(expression.Accept(NonNegatedDomainConstraintTreeVisitor <T_Variable, T_Element> .Instance));
}
internal override BoolExpr <T_Identifier> LocalSimplify(BoolExpr <T_Identifier> expression)
{
return(expression.Accept(Simplifier <T_Identifier> .Instance));
}
/// <summary> /// Performs local simplification appropriate to the current identifier. /// </summary> internal abstract BoolExpr <T_Identifier> LocalSimplify(BoolExpr <T_Identifier> expression);
internal override BoolExpr <DomainConstraint <T_Variable, T_Element> > LocalSimplify(BoolExpr <DomainConstraint <T_Variable, T_Element> > expression)
{
expression = NegationPusher.EliminateNot <T_Variable, T_Element>(expression);
return(expression.Accept(Simplifier <DomainConstraint <T_Variable, T_Element> > .Instance));
}
/// <summary>
/// Adds an equivalence to this KB, of the form:
///
/// left iff. right
/// </summary>
/// <param name="left">Left operand</param>
/// <param name="right">Right operand</param>
internal void AddEquivalence(BoolExpr <T_Identifier> left, BoolExpr <T_Identifier> right)
{
AddFact(new Equivalence(left, right));
}
/// <summary>
/// Adds the given implication to this KB, where implication is of the form:
///
/// condition --> implies
/// </summary>
/// <param name="condition">Condition</param>
/// <param name="implies">Entailed expression</param>
internal void AddImplication(BoolExpr <T_Identifier> condition, BoolExpr <T_Identifier> implies)
{
AddFact(new Implication(condition, implies));
}
/// <summary>
/// Initialize a new normal form node representing the given expression. Caller must
/// ensure the expression is logically equivalent to the node.
/// </summary>
/// <param name="expr">Expression logically equivalent to this node.</param>
protected NormalFormNode(BoolExpr <T_Identifier> expr)
{
_expr = expr.Simplify();
}
internal static int CountTerms(BoolExpr <T_Identifier> expression)
{
Debug.Assert(null != expression);
return(expression.Accept(s_instance));
}
public bool Equals(BoolExpr <T_Identifier> other)
{
return(null != other && ExprType == other.ExprType &&
EquivalentTypeEquals(other));
}
internal Converter(BoolExpr <T_Identifier> expr, ConversionContext <T_Identifier> context)
{
_context = context ?? IdentifierService <T_Identifier> .Instance.CreateConversionContext();
_vertex = ToDecisionDiagramConverter <T_Identifier> .TranslateToRobdd(expr, _context);
}
// (condition --> implies) iff. (!condition OR implies)
internal Implication(BoolExpr <T_Identifier> condition, BoolExpr <T_Identifier> implies)
: base(condition.MakeNegated(), implies)
{
_condition = condition;
_implies = implies;
}
