001    /*
002     * Copyright (c) 2005 Einar Pehrson <einar@pehrson.nu>.
003     *
004     * This file is part of
005     * CleanSheets - a spreadsheet application for the Java platform.
006     *
007     * CleanSheets is free software; you can redistribute it and/or modify
008     * it under the terms of the GNU General Public License as published by
009     * the Free Software Foundation; either version 2 of the License, or
010     * (at your option) any later version.
011     *
012     * CleanSheets is distributed in the hope that it will be useful,
013     * but WITHOUT ANY WARRANTY; without even the implied warranty of
014     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
015     * GNU General Public License for more details.
016     *
017     * You should have received a copy of the GNU General Public License
018     * along with CleanSheets; if not, write to the Free Software
019     * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
020     */
021    package csheets.core.formula.util;
022            
023    import csheets.core.Value;
024    import csheets.core.formula.BinaryOperation;
025    import csheets.core.formula.FunctionCall;
026    import csheets.core.formula.Literal;
027    import csheets.core.formula.Reference;
028    import csheets.core.formula.UnaryOperation;
029    
030    /**
031     * A base-class for customized formula interpreters. The interpretation relies
032     * on the Visitor pattern, so a typical invocation would look like
033     * <code>formula.accept(interpreter)</code>.
034     * @author Einar Pehrson
035     */
036    public abstract class Interpreter implements ExpressionVisitor {
037    
038            /**
039             * Creates a new interpreter.
040             */
041            public Interpreter() {}
042    
043            public Value visitLiteral(Literal literal) {
044                    return literal.evaluate();
045            }
046    
047            public abstract Value visitUnaryOperation(UnaryOperation operation);
048    
049            public abstract Value visitBinaryOperation(BinaryOperation operation);
050    
051            public Value visitReference(Reference reference) {
052                    return reference.evaluate();
053            }
054    
055            public abstract Value visitFunctionCall(FunctionCall call);
056    }