CODECOMPOSER: GEL check if symbol exists

Part Number: CODECOMPOSER

Tool/software:

Hi

In the GEL language is there a way to detect if a symbol is defined or not?

pseudo code example: 

OnHalt()
{
    if( defined( myMain ) )
    {
        GEL_Go(myMain):
    }
    else
    {
        GEL_Go(main);
    }
{