use newly available character type in must_be/2
list_of_chars(Cs) :-
must_be(list, Cs),
- ( ground(Cs) ->
- ( member(C, Cs), \+ atom_length(C, 1) ->
- type_error(char, C, files_and_directories)
- ; true
- )
- ; instantiation_error(s)
- ).
+ maplist(must_be(character), Cs).
directory_files(Directory, Files) :-
list_of_chars(Directory),
