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