// -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
//
// The contents of this file are subject to the Netscape Public
// License Version 1.1 (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.mozilla.org/NPL/
//
// Software distributed under the License is distributed on an "AS
// IS" basis, WITHOUT WARRANTY OF ANY KIND, either express oqr
// implied. See the License for the specific language governing
// rights and limitations under the License.
//
// The Original Code is the JavaScript 2 Prototype.
//
// The Initial Developer of the Original Code is Netscape
// Communications Corporation.  Portions created by Netscape are
// Copyright (C) 1998 Netscape Communications Corporation. All
// Rights Reserved.

/**
 * Opaque reference to a JavaScript object.
 */
class JSObject;

/**
 * Opaque reference to a general JavaScript identifier key.
 * This can represent both UNICODE strings, and other more
 * efficient representations, such as hashcodes, etc.
 */
class JSIdentifier;

/**
 * Some fundamental constants.
 */
#define	JSNULL (0)
#define JSUNDEFINED = ((JSObject*)(-1))

/**
 * Basic abstraction to associate names with values in a chain of scopes.
 * Can represent any kind of scope, including lexical scopes (closures),
 * namespaces, and classes. Access control can be implemented
 */
class JSScope {
public:
    /**
     * Gets the enclosing scope of this scope (if any).
     * @return enclosing scope or JSNULL if none.
     */
    virtual JSScope* getParent() = 0;

    /**
     * Defines a new identifier in the current scope. In a completely static
     * model, this may not be possible, and so this operation will be ignored.
     * @param start the evaluation scope
     * @param id identifier to define
     * @param value optional value to associate with id
     */
    virtual void defineValue(JSScope* start, JSIndentifier* id, JSObject* value = JSUNDEFINED) = 0;

    /**
     * Looks up a value corresponding to the given identifier starting
     * with the current scope, and proceeding up the scope chain. If
     * the identifier's is not defined in any of the scopes, the value
     * JSUNDEFINED is returned.
     * @param start the evaluation scope
     * @parm id the identifer to lookup
     * @return result of lookup or JSUNDEFINED
     */
    virtual JSObject* getValue(JSScope* start, JSIdentifier* id) = 0;
	
    /**
     * Associates a value with an identifier in a given scope.
     * @param start the evaluation scope
     * @param id identifier to assign to
     * @param value new value to give to id
     * @return old value associated with identifier
     */
    virtual JSObject* setValue(JSScope* start, JSIdentifier* id, JSObject* value) = 0;
};