private IEnumerable <BoolExpr <T_To> > VisitChildren(TreeExpr <T_From> expression)
{
foreach (BoolExpr <T_From> child in expression.Children)
{
yield return(child.Accept(this));
}
}
private bool VisitTree(TreeExpr <T_Identifier> expression)
{
foreach (BoolExpr <T_Identifier> child in expression.Children)
{
child.Accept(this);
}
return(true);
}
private int VisitTree(TreeExpr <T_Identifier> expression)
{
int sum = 0;
foreach (var child in expression.Children)
{
sum += child.Accept(this);
}
return(sum);
}
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);
}
}
