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Closure Stylesheets is an extension to CSS that adds variables, functions, conditionals, and mixins to standard CSS. The tool also supports minification, linting, RTL flipping, and CSS class renaming.

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/*
 * Copyright 2009 Google Inc.
 *
 * Licensed 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.
 */

package com.google.common.css.compiler.ast;

import java.util.List;

/**
 * Encapsulates a custom function callable from GSS stylesheet files.
 */

public interface GssFunction {

    /**
     * Returns the number of parsed arguments that this function takes,
     * or {@code null} if the number of arguments may vary.
     */
    Integer getNumExpectedArguments();

    /**
     * Processes a list of function call arguments and returns a list of
     * CssNodes representing this call's output, which replace the input
     * nodes in the AST. Errors will be reported to the ErrorManager.
     */
    List getCallResultNodes(
            List args, ErrorManager errorManager)
            throws GssFunctionException;

    /**
     * Processes a list of strings as function arguments and returns a string
     * result. Errors are reported by throwing {@link GssFunctionException}.
     */
    String getCallResultString(List args) throws GssFunctionException;
}