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//
// QueryParser.cc
//
// QueryParser: (abstract) root of the family of classes that create
// Query trees by analyzing query strings.
// The main public interface consists on Parse(),
// which does the job.
// The subclasses must provide a lexer.
// This class implements also the common behaviour needed to
// parse single words and phrases.
//
// 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: QueryParser.cc,v 1.4 2004/05/28 13:15:24 lha Exp $
//
#include "QueryParser.h"
#include "Query.h"
#include "htString.h"
#include "ExactWordQuery.h"
#include "PhraseQuery.h"
#include "FuzzyExpander.h"
extern int debug;
FuzzyExpander *
QueryParser::expander = 0;
//
// parse a query string
//
//
Query *
QueryParser::Parse(const String &query_string)
{
error = "";
Token().Set(query_string);
Query *result = ParseExpression();
if(result && !Token().IsEnd())
{
Expected("end of query");
// delete result;
result = 0;
}
return result;
}
// parse one word
// return a fuzzy word query
//
Query *
QueryParser::ParseWord()
{
Query *result = 0;
if(expander)
{
result = expander->MakeQuery(Token().Value());
}
else
{
result = new ExactWordQuery(Token().Value());
}
Token().Next();
return result;
}
//
// parse one word
// return an exact query
//
Query *
QueryParser::ParseExactWord()
{
Query *result = new ExactWordQuery(Token().Value());
Token().Next();
return result;
}
//
// phrase == word { word }
//
Query *
QueryParser::ParsePhrase()
{
Query *result = 0;
Query *word = 0;
if(!Token().IsEnd() && !Token().IsQuote())
{
word = ParseExactWord();
}
if(word)
{
result = new PhraseQuery;
result->Add(word);
while(word && !Token().IsEnd() && !Token().IsQuote())
{
word = ParseExactWord();
if(word)
{
result->Add(word);
}
}
}
if(!word && result)
{
delete result;
result = 0;
}
if(!result)
{
Expected("at least one word after \"");
}
return result;
}
void
QueryParser::Expected(const String &what)
{
error << "Expected " << what;
if(Token().IsEnd())
{
error << " at the end";
}
else
{
error << " instead of '" << Token().Value() << "'";
}
}
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