private static bool TryTakeExpression(TokenKeeper tokenKeeper, out FilterClause clause)
{
if (TryTakeParenExpression(tokenKeeper, out clause) ||
TryTakeComparison(tokenKeeper, out clause))
{
var work = new TokenKeeper(tokenKeeper);
if (TryTakeRelOp(work, ref clause))
{
tokenKeeper.Swap(work);
}
return(true);
}
clause = null;
return(false);
}
private static bool TryTakeComparison(TokenKeeper tokenKeeper, out FilterClause clause)
{
Token left, right, op;
var work = new TokenKeeper(tokenKeeper);
if (TryTakeData(work, out left) && TryTakeOperator(work, out op) &&
TryTakeData(work, out right))
{
tokenKeeper.Swap(work);
clause = new ComparisonClause(left, op, right);
return(true);
}
clause = null;
return(false);
}
private static bool TryTakeRelOp(TokenKeeper tokenKeeper, ref FilterClause clause)
{
if (tokenKeeper.Next.IsRelop())
{
var work = new TokenKeeper(tokenKeeper);
var op = work.Take();
FilterClause rhs;
if (TryTakeExpression(work, out rhs))
{
var relOpClause = new RelOpClause(clause, op, rhs);
tokenKeeper.Swap(work);
clause = relOpClause;
return(true);
}
}
return(false);
}
private static bool TryTakeParenExpression(TokenKeeper tokenKeeper, out FilterClause clause)
{
if (tokenKeeper.Next.TokenType == TokenType.OpenParen)
{
var work = new TokenKeeper(tokenKeeper);
work.Take();
FilterClause expression;
if (TryTakeExpression(work, out expression) && work.Next.TokenType == TokenType.CloseParen)
{
work.Take();
clause = new ParenClause(expression);
tokenKeeper.Swap(work);
return(true);
}
}
clause = null;
return(false);
}
public RelOpClause(FilterClause lhs, Token op, FilterClause rhs)
{
Lhs = lhs;
Op = op;
Rhs = rhs;
}
public ParenClause(FilterClause clause)
{
Clause = clause;
}
