function getter(instance, path, unboundFn) {
  if (!path) return instance;
  var element = path.split('.');
  var key;
  var lastInstance = instance;
  var len = element.length;
  for ( var i = 0; i < len; i++) {
    key = element[i];
    if (!key.match(/^[\$\w][\$\w\d]*$/))
        throw "Expression '" + path + "' is not a valid expression for accesing variables.";
    if (instance) {
      lastInstance = instance;
      instance = instance[key];
    }
    if (isUndefined(instance)  && key.charAt(0) == '$') {
      var type = angular['Global']['typeOf'](lastInstance);
      type = angular[type.charAt(0).toUpperCase()+type.substring(1)];
      var fn = type ? type[[key.substring(1)]] : _undefined;
      if (fn) {
        instance = bind(lastInstance, fn, lastInstance);
        return instance;
      }
    }
  }
  if (!unboundFn && isFunction(instance)) {
    return bind(lastInstance, instance);
  }
  return instance;
}

function setter(instance, path, value){
  var element = path.split('.');
  for ( var i = 0; element.length > 1; i++) {
    var key = element.shift();
    var newInstance = instance[key];
    if (!newInstance) {
      newInstance = {};
      instance[key] = newInstance;
    }
    instance = newInstance;
  }
  instance[element.shift()] = value;
  return value;
}

///////////////////////////////////
var scopeId = 0,
    getterFnCache = {},
    compileCache = {},
    JS_KEYWORDS = {};
foreach(
   ["abstract", "boolean", "break", "byte", "case", "catch", "char", "class", "const", "continue", "debugger", "default",
    "delete", "do", "double", "else", "enum", "export", "extends", "false", "final", "finally", "float", "for", $function, "goto",
    "if", "implements", "import", "ininstanceof", "intinterface", "long", "native", "new", $null, "package", "private",
    "protected", "public", "return", "short", "static", "super", "switch", "synchronized", "this", "throw", "throws",
    "transient", "true", "try", "typeof", "var", "volatile", "void", $undefined, "while", "with"],
  function(key){ JS_KEYWORDS[key] = true;}
);
function getterFn(path){
  var fn = getterFnCache[path];
  if (fn) return fn;

  var code = 'function (s){\n';
  code += '  var l, fn, t;\n';
  foreach(path.split('.'), function(key) {
    key = (JS_KEYWORDS[key]) ? '["' + key + '"]' : '.' + key;
    code += '  if(!s) return s;\n';
    code += '  l = s;\n';
    code += '  s = s' + key + ';\n';
    code += '  if(typeof s == "'+$function+'") \n';
    code += '    s = function(){ return l'+key+'.apply(l, arguments); };\n';
    if (key.charAt(1) == '$') {
      // special code for super-imposed functions
      var name = key.substr(2);
      code += '  if(!s) {\n';
      code += '    t = angular.Global.typeOf(l);\n';
      code += '    fn = (angular[t.charAt(0).toUpperCase() + t.substring(1)]||{})["' + name + '"];\n';
      code += '    if (fn)\n';
      code += '      s = function(){ return fn.apply(l, [l].concat(Array.prototype.slice.call(arguments, 0, arguments.length))); };\n';
      code += '  }\n';
    }
  });
  code += '  return s;\n}';
  fn = eval('fn = ' + code);
  fn["toString"] = function(){ return code; };

  return getterFnCache[path] = fn;
}

///////////////////////////////////

function expressionCompile(exp){
  if (typeof exp === $function) return exp;
  var fn = compileCache[exp];
  if (!fn) {
    var parser = new Parser(exp);
    var fnSelf = parser.statements();
    parser.assertAllConsumed();
    fn = compileCache[exp] = extend(
      function(){ return fnSelf(this);},
      {fnSelf: fnSelf});
  }
  return fn;
}

function rethrow(e) { throw e; }
function errorHandlerFor(element, error) {
  elementError(element, NG_EXCEPTION, isDefined(error) ? toJson(error) : error);
}

function createScope(parent, services, existing) {
  function Parent(){}
  function API(){}
  function Behavior(){}

  parent = Parent.prototype = (parent || {});
  var evalLists = {sorted:[]};
  var postList = [], postHash = {}, postId = 0;
  var servicesCache = extend({}, existing);
  var api = API.prototype = new Parent();
  var behavior = Behavior.prototype = new API();
  var instance = new Behavior();

  extend(api, {
    'this': instance,
    $id: (scopeId++),
    $parent: parent,
    $bind: bind(instance, bind, instance),
    $get: bind(instance, getter, instance),
    $set: bind(instance, setter, instance),

    $eval: function $eval(exp) {
      var type = typeof exp;
      var i, iSize;
      var j, jSize;
      var queue;
      var fn;
      if (type == $undefined) {
        for ( i = 0, iSize = evalLists.sorted.length; i < iSize; i++) {
          for ( queue = evalLists.sorted[i],
              jSize = queue.length,
              j= 0; j < jSize; j++) {
            instance.$tryEval(queue[j].fn, queue[j].handler);
          }
        }
        while(postList.length) {
          fn = postList.shift();
          delete postHash[fn.$postEvalId];
          instance.$tryEval(fn);
        }
      } else if (type === $function) {
        return exp.call(instance);
      } else  if (type === 'string') {
        return expressionCompile(exp).call(instance);
      }
    },

    $tryEval: function (expression, exceptionHandler) {
      var type = typeof expression;
      try {
        if (type == $function) {
          return expression.call(instance);
        } else if (type == 'string'){
          return expressionCompile(expression).call(instance);
        }
      } catch (e) {
        (instance.$log || {error:error}).error(e);
        if (isFunction(exceptionHandler)) {
          exceptionHandler(e);
        } else if (exceptionHandler) {
          errorHandlerFor(exceptionHandler, e);
        } else if (isFunction(instance.$exceptionHandler)) {
          instance.$exceptionHandler(e);
        }
      }
    },

    $watch: function(watchExp, listener, exceptionHandler) {
      var watch = expressionCompile(watchExp),
          last;
      listener = expressionCompile(listener);
      function watcher(){
        var value = watch.call(instance),
            lastValue = last;
        if (last !== value) {
          last = value;
          instance.$tryEval(function(){
            return listener.call(instance, value, lastValue);
          }, exceptionHandler);
        }
      }
      instance.$onEval(PRIORITY_WATCH, watcher);
      watcher();
    },

    $onEval: function(priority, expr, exceptionHandler){
      if (!isNumber(priority)) {
        exceptionHandler = expr;
        expr = priority;
        priority = 0;
      }
      var evalList = evalLists[priority];
      if (!evalList) {
        evalList = evalLists[priority] = [];
        evalList.priority = priority;
        evalLists.sorted.push(evalList);
        evalLists.sorted.sort(function(a,b){return a.priority-b.priority;});
      }
      evalList.push({
        fn: expressionCompile(expr),
        handler: exceptionHandler
      });
    },

    $postEval: function(expr) {
      if (expr) {
        var fn = expressionCompile(expr);
        var id = fn.$postEvalId;
        if (!id) {
          id = '$' + instance.$id + "_" + (postId++);
          fn.$postEvalId = id;
        }
        if (!postHash[id]) {
          postList.push(postHash[id] = fn);
        }
      }
    },

    $become: function(Class) {
      // remove existing
      foreach(behavior, function(value, key){ delete behavior[key]; });
      foreach((Class || noop).prototype, function(fn, name){
        behavior[name] = bind(instance, fn);
      });
      (Class || noop).call(instance);

      //TODO: backwards compatibility hack, remove when Feedback's init methods are removed
      if (behavior.hasOwnProperty('init')) {
        behavior.init();
      }
    }

  });

  if (!parent.$root) {
    api.$root = instance;
    api.$parent = instance;
  }

  function inject(name){
    var service = servicesCache[name], factory, args = [];
    if (isUndefined(service)) {
      factory = services[name];
      if (!isFunction(factory))
        throw "Don't know how to inject '" + name + "'.";
      foreach(factory.inject, function(dependency){
        args.push(inject(dependency));
      });
      servicesCache[name] = service = factory.apply(instance, args);
    }
    return service;
  }

  foreach(services, function(_, name){
    var service = inject(name);
    if (service) {
      setter(instance, name, service);
    }
  });

  return instance;
}