src/java/org/apache/fop/fo/expr/Function.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/* $Id$ */

package org.apache.fop.fo.expr;

import org.apache.fop.fo.properties.Property;
import org.apache.fop.datatypes.PercentBase;

/**
 * Interface for managing XSL-FO Functions
 */
public interface Function {

    /**
     * @return the number of arguments that must be passed to this function. For
     * example, if the function should determine the minimum of two numbers, it
     * must be passed two arguments, one for each of the two values.
     */
    int nbArgs();

    /**
     * @return the basis for percentage calculations
     */
    PercentBase getPercentBase();

    /**
     * Evaluate the function
     * @param args an array of Properties that should be evaluated
     * @param propInfo the PropertyInfo
     * @return the Property satisfying the function
     * @throws PropertyException for problems when evaluating the function
     */
    Property eval(Property[] args,
                  PropertyInfo propInfo) throws PropertyException;

    /**
     * @return if it is allowed to fill up the property list with
     * the property name if only one arg is missing.
     */
    boolean padArgsWithPropertyName();
}