/// <summary>
        /// Checks the expression and appends errors to the root tree node when inconsistencies are found
        /// </summary>
        public override void checkExpression()
        {
            base.checkExpression();

            Called.checkExpression();
            ICallable called = Called.getStaticCallable();

            if (called != null)
            {
                if (called.FormalParameters.Count != NamedActualParameters.Count + ActualParameters.Count)
                {
                    AddError("Invalid number of arguments provided for function call " + ToString() + " expected " + called.FormalParameters.Count + " actual " + NamedActualParameters.Count);
                }
                else
                {
                    Dictionary <string, Expression> actuals = new Dictionary <string, Expression>();

                    int i = 0;
                    foreach (Expression expression in ActualParameters)
                    {
                        Parameter parameter = called.FormalParameters[i] as Parameter;
                        CheckActualAgainstFormal(actuals, expression, parameter);
                        i = i + 1;
                    }

                    foreach (KeyValuePair <string, Expression> pair in NamedActualParameters)
                    {
                        string     name       = pair.Key;
                        Expression expression = pair.Value;
                        Parameter  parameter  = called.getFormalParameter(name);
                        if (parameter == null)
                        {
                            AddError("Parameter " + name + " is not defined as formal parameter of function " + called.FullName);
                        }
                        else
                        {
                            if (actuals.ContainsKey(name))
                            {
                                AddError("Parameter " + name + " isassigned twice in " + ToString());
                            }
                            else
                            {
                                CheckActualAgainstFormal(actuals, expression, parameter);
                            }
                        }
                    }

                    if (called.FormalParameters.Count > 2)
                    {
                        if (ActualParameters.Count > 0)
                        {
                            AddWarning("Calls where more than two parameters are provided must be performed using named association");
                        }
                    }

                    called.additionalChecks(Root, actuals);
                }
            }
            else
            {
                AddError("Cannot determine callable referenced by " + ToString());
            }
        }