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 */
021package csheets.core.formula.lang;
022
023import csheets.core.IllegalValueTypeException;
024import csheets.core.Value;
025import csheets.core.formula.Expression;
026import csheets.core.formula.Function;
027import csheets.core.formula.FunctionParameter;
028
029/**
030 * A function that returns the factorial of its argument.
031 * @author Einar Pehrson
032 */
033public 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}