001    /*
002    // $Id: //open/mondrian-release/3.0/src/main/mondrian/olap/Exp.java#2 $
003    // This software is subject to the terms of the Common Public License
004    // Agreement, available at the following URL:
005    // http://www.opensource.org/licenses/cpl.html.
006    // Copyright (C) 1999-2002 Kana Software, Inc.
007    // Copyright (C) 2001-2006 Julian Hyde and others
008    // All Rights Reserved.
009    // You must accept the terms of that agreement to use this software.
010    //
011    // jhyde, 20 January, 1999
012    */
013    
014    package mondrian.olap;
015    
016    import mondrian.olap.type.Type;
017    import mondrian.calc.Calc;
018    import mondrian.calc.ExpCompiler;
019    import mondrian.mdx.MdxVisitorImpl;
020    import mondrian.mdx.MdxVisitor;
021    
022    import java.io.PrintWriter;
023    
024    /**
025     * An <code>Exp</code> is an MDX expression.
026     *
027     * @author jhyde
028     * @since 1.0
029     * @version $Id: //open/mondrian-release/3.0/src/main/mondrian/olap/Exp.java#2 $
030     */
031    public interface Exp {
032    
033        Exp clone();
034    
035        /**
036         * Returns the {@link Category} of the expression.
037         *
038         * @post Category.instance().isValid(return)
039         */
040        int getCategory();
041    
042        /**
043         * Returns the type of this expression. Never null.
044         */
045        Type getType();
046    
047        /**
048         * Writes the MDX representation of this expression to a print writer.
049         * Sub-expressions are invoked recursively.
050         *
051         * @param pw PrintWriter
052         */
053        void unparse(PrintWriter pw);
054    
055        /**
056         * Validates this expression.
057         *
058         * The validator acts in the role of 'visitor' (see Gang of Four
059         * 'visitor pattern'), and an expression in the role of 'visitee'.
060         *
061         * @param validator Validator contains validation context
062         *
063         * @return The validated expression; often but not always the same as
064         *   this expression
065         */
066        Exp accept(Validator validator);
067    
068        /**
069         * Converts this expression into an a tree of expressions which can be
070         * efficiently evaluated.
071         *
072         * @param compiler
073         * @return A compiled expression
074         */
075        Calc accept(ExpCompiler compiler);
076    
077        /**
078         * Accepts a visitor to this Exp.
079         * The implementation should generally dispatches to the
080         * {@link MdxVisitor#visit} method appropriate to the type of expression.
081         *
082         * @param visitor Visitor
083         */
084        Object accept(MdxVisitor visitor);
085    }
086    
087    // End Exp.java