% Figure 4.5 A flight route planner and an example flight timetable.
% A FLIGHT ROUTE PLANNER
:- op( 50, xfy, :).
% route( Place1, Place2, Day, Route):
% Route is a sequence of flights on Day, starting at Place1, ending at Place2
route( P1, P2, Day, [ P1 / P2 / Fnum / Deptime ] ) :- % Direct flight
flight( P1, P2, Day, Fnum, Deptime, _).
route( P1, P2, Day, [ (P1 / P3 / Fnum1 / Dep1) | RestRoute] ) :- % Indirect connection
route( P3, P2, Day, RestRoute),
flight( P1, P3, Day, Fnum1, Dep1, Arr1),
deptime( RestRoute, Dep2), % Departure time of Route
transfer( Arr1, Dep2). % Enough time for transfer
flight( Place1, Place2, Day, Fnum, Deptime, Arrtime) :-
timetable( Place1, Place2, Flightlist),
member( Deptime / Arrtime / Fnum / Daylist , Flightlist),
flyday( Day, Daylist).
flyday( Day, Daylist) :-
member( Day, Daylist).
flyday( Day, alldays) :-
member( Day, [mo,tu,we,th,fr,sa,su] ).
deptime( [ P1 / P2 / Fnum / Dep | _], Dep).
transfer( Hours1:Mins1, Hours2:Mins2) :-
60 * (Hours2 - Hours1) + Mins2 - Mins1 >= 40.
member( X, [X | L] ).
member( X, [Y | L] ) :-
member( X, L).
% A FLIGHT DATABASE
timetable( edinburgh, london,
[ 9:40 / 10:50 / ba4733 / alldays,
13:40 / 14:50 / ba4773 / alldays,
19:40 / 20:50 / ba4833 / [mo,tu,we,th,fr,su] ] ).
timetable( london, edinburgh,
[ 9:40 / 10:50 / ba4732 / alldays,
11:40 / 12:50 / ba4752 / alldays,
18:40 / 19:50 / ba4822 / [mo,tu,we,th,fr] ] ).
timetable( london, ljubljana,
[ 13:20 / 16:20 / jp212 / [mo,tu,we,fr,su],
16:30 / 19:30 / ba473 / [mo,we,th,sa] ] ).
timetable( london, zurich,
[ 9:10 / 11:45 / ba614 / alldays,
14:45 / 17:20 / sr805 / alldays ] ).
timetable( london, milan,
[ 8:30 / 11:20 / ba510 / alldays,
11:00 / 13:50 / az459 / alldays ] ).
timetable( ljubljana, zurich,
[ 11:30 / 12:40 / jp322 / [tu,th] ] ).
timetable( ljubljana, london,
[ 11:10 / 12:20 / jp211 / [mo,tu,we,fr,su],
20:30 / 21:30 / ba472 / [mo,we,th,sa] ] ).
timetable( milan, london,
[ 9:10 / 10:00 / az458 / alldays,
12:20 / 13:10 / ba511 / alldays ] ).
timetable( milan, zurich,
[ 9:25 / 10:15 / sr621 / alldays,
12:45 / 13:35 / sr623 / alldays ] ).
timetable( zurich, ljubljana,
[ 13:30 / 14:40 / jp323 / [tu,th] ] ).
timetable( zurich, london,
[ 9:00 / 9:40 / ba613 / [mo,tu,we,th,fr,sa],
16:10 / 16:55 / sr806 / [mo,tu,we,th,fr,su] ] ).
timetable( zurich, milan,
[ 7:55 / 8:45 / sr620 / alldays ] ).
query3(City1,City2,City3,FN1,FN2,FN3,FN4) :-
permutation( [milan,ljubljana,zurich],[City1,City2,City3]),
flight( london, City1, tu, FN1, Dep1, Arr1),
flight( City1, City2, we, FN2, Dep2, Arr2),
flight( City2, City3, th, FN3, Dep3, Arr3),
flight( City3, london, fr, FN4, Dep4, Arr4).
conc([], L, L).
conc([X|L1],L2, [X|L3]) :-
conc(L1,L2,L3).
permutation( [], []).
permutation( L, [X | P]) :-
del( X, L, L1),
permutation( L1, P).
del( X, [X|L], L).
del( X, [Y|L], [Y|L1]) :-
del( X, L, L1).