These tests provide access to source related information.  The
file and line tests will fail if no source information is
present. The parent_clause and parent_pred tests are
available for interpreted code only, they will fail in
compiled code.
     
file(File)
     line(File,Line)
     line(Line)
     parent_clause(Cl)
     parent_clause(Cl,Sel)
     parent_clause(Cl,Sel,I)
     parent_pred(Pred)
     parent_pred(Pred,N)
     The parent_pred tests match their first argument against
the functor of the parent predicate in the same way as
the pred test does, see the notes in the previous section
(Goal Tests).