correct error reporting for variable_names write option
@@ -249,6 +249,7 @@ must_be_var_names_list_([]).
must_be_var_names_list_([VarName | VarNames]) :-
( nonvar(VarName), VarName = (Atom = _) ->
( atom(Atom) -> must_be_var_names_list_(VarNames)
+ ; var(Atom) -> throw(error(instantiation_error, write_term/2))
; throw(error(domain_error(write_options, variable_names(VarName)), write_term/2))
)
; throw(error(domain_error(write_options, variable_names(VarName)), write_term/2))
