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The Apache Commons JEXL library is an implementation of the JSTL Expression Language with extensions.
There is a newer version: 3.4.0
/*
 * 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.
 */
package org.apache.commons.jexl3.parser;

import org.apache.commons.jexl3.internal.Scope;
import java.util.Map;

/**
 * Enhanced script to allow parameters declaration.
 */
public class ASTJexlScript extends JexlNode {
    /** The script scope. */
    private Scope scope = null;
    /** The pragmas. */
    Map pragmas = null;

    public ASTJexlScript(int id) {
        super(id);
    }

    public ASTJexlScript(Parser p, int id) {
        super(p, id);
    }

    /**
     * Consider script with no parameters that return lambda as parametric-scripts.
     * @return the script
     */
    public ASTJexlScript script() {
        if (scope == null && jjtGetNumChildren() == 1 && jjtGetChild(0) instanceof ASTJexlLambda) {
            ASTJexlLambda lambda = (ASTJexlLambda) jjtGetChild(0);
            lambda.jjtSetParent(null);
            return lambda;
        } else {
            return this;
        }
    }

    @Override
    public Object jjtAccept(ParserVisitor visitor, Object data) {
        return visitor.visit(this, data);
    }

    /**
     * Coerce this script as an expression (ie only one child) if necessary.
     * @return true if the script was coerced, false otherwise
     */
    public boolean toExpression() {
        if (jjtGetNumChildren() > 1) {
            jjtSetChildren(new JexlNode[]{jjtGetChild(0)});
            return true;
        } else {
            return false;
        }
    }

    /**
     * Sets this script scope.
     * @param theScope the scope
     */
    public void setScope(Scope theScope) {
        this.scope = theScope;
    }

    /**
     * @return this script scope
     */
    public Scope getScope() {
        return scope;
    }

    /**
     * @return this script pragmas
     */
    public Map getPragmas() {
        return pragmas;
    }

    /**
     * Creates an array of arguments by copying values up to the number of parameters.
     * @param values the argument values
     * @return the arguments array
     */
    public Scope.Frame createFrame(Object... values) {
        if (scope != null) {
            Scope.Frame frame = scope.createFrame(null);
            if (frame != null) {
                return frame.assign(values);
            }
        }
        return null;
    }

    /**
     * Gets the (maximum) number of arguments this script expects.
     * @return the number of parameters
     */
    public int getArgCount() {
        return scope != null? scope.getArgCount() : 0;
    }

    /**
     * Gets this script symbols, i.e. parameters and local variables.
     * @return the symbol names
     */
    public String[] getSymbols() {
        return scope != null? scope.getSymbols() : null;
    }

    /**
     * Gets this script parameters, i.e. symbols assigned before creating local variables.
     * @return the parameter names
     */
    public String[] getParameters() {
        return scope != null? scope.getParameters() : null;
    }

    /**
     * Gets this script local variable, i.e. symbols assigned to local variables.
     * @return the local variable names
     */
    public String[] getLocalVariables() {
        return scope != null? scope.getLocalVariables() : null;
    }

    /**
     * Checks whether a given symbol is hoisted.
     * @param symbol the symbol number
     * @return true if hoisted, false otherwise
     */
    public boolean isHoistedSymbol(int symbol) {
        return scope != null? scope.isHoistedSymbol(symbol) : false;
    }
}