001    /*
002     * Copyright (C) 2010 eXo Platform SAS.
003     *
004     * This is free software; you can redistribute it and/or modify it
005     * under the terms of the GNU Lesser General Public License as
006     * published by the Free Software Foundation; either version 2.1 of
007     * the License, or (at your option) any later version.
008     *
009     * This software is distributed in the hope that it will be useful,
010     * but WITHOUT ANY WARRANTY; without even the implied warranty of
011     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
012     * Lesser General Public License for more details.
013     *
014     * You should have received a copy of the GNU Lesser General Public
015     * License along with this software; if not, write to the Free
016     * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
017     * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
018     */
019    
020    package org.crsh.shell.impl;
021    
022    import org.crsh.command.SyntaxException;
023    
024    /**
025     * @author <a href="mailto:julien.viet@exoplatform.com">Julien Viet</a>
026     * @version $Revision$
027     */
028    class Parser {
029    
030      /** . */
031      private Tokenizer tokenizer;
032    
033      /** . */
034      private Token token;
035    
036      public Parser(CharSequence s) {
037        this.tokenizer = new Tokenizer(s);
038        this.token = tokenizer.nextToken();
039      }
040    
041    
042      /*
043    
044      grammar
045    
046      expr -> term | term "|" expr
047      term -> cmd | cmd "+" term
048    
049       */
050    
051      public AST parse() {
052        if (token == Token.EOF) {
053          return null;
054        } else {
055          return parseExpr();
056        }
057      }
058    
059      private AST.Expr parseExpr() {
060        AST.Term term = parseTerm();
061        if (token == Token.EOF) {
062          return new AST.Expr(term);
063        } else if (token == Token.PIPE) {
064          token = tokenizer.nextToken();
065          AST.Expr next = parseExpr();
066          return new AST.Expr(term, next);
067        } else {
068          throw new SyntaxException("Syntax error");
069        }
070      }
071    
072      private AST.Term parseTerm() {
073        if (token instanceof Token.Command) {
074          Token.Command command = (Token.Command)token;
075          token = tokenizer.nextToken();
076          if (token == Token.PLUS) {
077            token = tokenizer.nextToken();
078            AST.Term next = parseTerm();
079            return new AST.Term(command.line, next);
080          } else {
081            return new AST.Term(command.line);
082          }
083        } else {
084          throw new SyntaxException("Syntax error");
085        }
086      }
087    }