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//
// GParser.cc
//
// GParser: An alternate boolean parser, does not use operator precedence.
// -- but why is it called G? :-)
//
// Part of the ht://Dig package <http://www.htdig.org/>
// Copyright (c) 1995-2004 The ht://Dig Group
// For copyright details, see the file COPYING in your distribution
// or the GNU Library General Public License (LGPL) version 2 or later
// <http://www.gnu.org/copyleft/lgpl.html>
//
// $Id: GParser.cc,v 1.4 2004/05/28 13:15:24 lha Exp $
//
#include "GParser.h"
#include "OrQuery.h"
#include "NearQuery.h"
#include "AndQuery.h"
#include "NotQuery.h"
Query *
GParser::ParseFactor()
{
Query *result = 0;
if(token.IsWord())
{
result = ParseWord();
}
else if(token.IsQuote())
{
token.Next();
result = ParsePhrase();
if(result)
{
if(token.IsQuote())
{
token.Next();
}
else
{
Expected("closing \"");
delete result;
result = 0;
}
}
}
else if(token.IsLeftParen())
{
token.Next();
result = ParseExpression();
if(result)
{
if(token.IsRightParen())
{
token.Next();
}
else
{
Expected(")");
delete result;
result = 0;
}
}
}
else
{
Expected("'(', '\"', or a word");
}
return result;
}
OperatorQuery *
GParser::MakeOperatorQuery(const String &op) const
{
cerr << "Making operator for " << op << endl;
OperatorQuery *result = 0;
if(op == String("or"))
{
result = new OrQuery;
}
else if(op == String("and"))
{
result = new AndQuery;
}
else if(op == String("not"))
{
result = new NotQuery;
}
else if(op == String("near"))
{
result = new NearQuery;
}
return result;
}
Query *
GParser::ParseExpression()
{
List factors;
Query *result = 0;
String op = "";
Query *factor = ParseFactor();
if(factor)
{
result = factor;
}
while(factor && (token.IsOr() || token.IsAnd() || token.IsNot() || token.IsNear()))
{
if(op != token.Value())
{
Query *previous = result;
result = MakeOperatorQuery(token.Value());
result->Add(previous);
op = token.Value();
}
token.Next();
factor = ParseFactor();
if(factor)
{
result->Add(factor);
}
}
if(!factor && result)
{
delete result;
result = 0;
}
return result;
}
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