:- object(plan(_)).
:- info([
author is 'Paulo Moura',
version is 1.0,
date is 2000/4/22,
comment is 'Air-line trip planner.',
parnames is ['Mode'],
source is 'Example adopted from the Francis G. McCabe L&O documentation.']).
:- public(from/3).
:- mode(from(+atom, +atom, -list), zero_or_more).
:- info(from/3,
[comment is 'Plan a trip from Start to Destination.',
argnames is ['Start', 'Destination', 'Plan']]).
from(Start, Destination, Plan) :-
from(Start, Destination, [], Plan).
from(Start, Destination, _, [Step]) :-
parameter(1, Mode),
Mode::step(Start, Destination, Step),
!.
from(Start, Destination, Locations, [Step| Steps]) :-
Mode::step(Start, City2, Step),
not_member(City2, Locations),
from(City2, Destination, [Start| Locations], Steps).
not_member(_, []).
not_member(City, [Location| Locations]) :-
City \= Location,
not_member(City, Locations).
:- end_object.
