Determine current (error) location in a lazy list. True when
Location is an (error) location term that represents the current
location in the DCG list.
- is a term file(Name, Line, LinePos, CharNo) or
stream(Stream, Line, LinePos, CharNo) if no file is
associated to the stream RestLazyList. Finally, if the
Lazy list is fully materialized (ends in ), Location
is unified with end_of_file-CharCount.