protected override Expression VisitUnary(UnaryExpression unaryExpression)
{
Check.NotNull(unaryExpression, nameof(unaryExpression));
if (unaryExpression.NodeType == ExpressionType.Not &&
unaryExpression.IsLogicalNot())
{
if (unaryExpression.Operand is ConstantExpression innerConstant &&
innerConstant.Value is bool value)
{
// !(true) -> false
// !(false) -> true
return(Expression.Constant(!value));
}
if (unaryExpression.Operand is UnaryExpression innerUnary &&
innerUnary.NodeType == ExpressionType.Not)
{
// !(!a) -> a
return(Visit(innerUnary.Operand));
}
if (unaryExpression.Operand is BinaryExpression innerBinary)
{
// De Morgan's
if (innerBinary.NodeType == ExpressionType.AndAlso ||
innerBinary.NodeType == ExpressionType.OrElse)
{
return(Visit(
Expression.MakeBinary(
Negate(innerBinary.NodeType),
Expression.Not(innerBinary.Left),
Expression.Not(innerBinary.Right))));
}
if (TryNegate(innerBinary.NodeType, out var negated))
{
return(Visit(
Expression.MakeBinary(
negated,
innerBinary.Left,
innerBinary.Right)));
}
}
}
return(base.VisitUnary(unaryExpression));
}