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.lang;
022    
023    import csheets.core.IllegalValueTypeException;
024    import csheets.core.Value;
025    import csheets.core.formula.Expression;
026    import csheets.core.formula.Function;
027    import csheets.core.formula.FunctionParameter;
028    
029    /**
030     * A function that returns the factorial of its argument.
031     * @author Einar Pehrson
032     */
033    public class Factorial implements Function {
034    
035            /** The only parameter: a numeric term */
036            public static final FunctionParameter[] parameters = new FunctionParameter[] {
037                    new FunctionParameter(Value.Type.NUMERIC, "Number", false,
038                            "The positive integer for which to calculate the factorial")
039            };
040    
041            /**
042             * Creates a new instance of the FACT function.
043             */
044            public Factorial() {}
045    
046            public String getIdentifier() {
047                    return "FACT";
048            }
049    
050            public Value applyTo(Expression[] arguments) throws IllegalValueTypeException {
051                    double number = arguments[0].evaluate().toDouble();
052                    if (number >= 1 && number == Math.round(number)) {
053                            int factorial = 1;
054                            for (int i = 2; i <= number; i++)
055                                    factorial *= i;
056                            return new Value(factorial);
057                    } else
058                            return new Value(new IllegalArgumentException("Argument must be a positive integer"));
059            }
060    
061            public FunctionParameter[] getParameters() {
062                    return parameters;
063            }
064    
065            public boolean isVarArg() {
066                    return false;
067            }
068    }