Return_Value

   An integer value if you are converting an identifier from a name
   to an integer. The F$IDENTIFIER function returns a string if
   you are converting an identifier from an integer to a name. If
   you specify an identifier that is not valid, the F$IDENTIFIER
   function returns a null string ("")  (if you are converting from
   number to name) or a zero (if you are converting from name to
   number).