Applying Logical Knowledge

  Exercises

Update travel.pro

see, tell(FILENAME) redirects I/O to that file.

seen, told redirects I/O back to the console.

reconsult(FILENAME) consults predicates in a file, first erasing any previous in-memory clauses of the same functor/arity.

• Comment out /* ... */ the passenger & booking facts in flight_data.pro.
• Create a CourseAir command add_passenger/0, to read passenger information and assert a new passenger/3 clause.
• Create book_passenger(FLIGHT, LAST_NAME, FIRST_NAME) that creates a new booked/2 clause..
• Create next_id/1 that retracts current_id/1, increments the value, and asserts a new current_id/1 that can be used to generate passenger IDs.
  

  next_id(NEXT) :-
     retract(current_id(CURRENT)),
     NEXT is CURRENT + 1,
     assert(current_id(NEXT)).

• Save and Restore the booking data:
  • save_data :- tell('passenger_data.pro'), listing(passenger), listing(booking), listing(current_id), told.
  • restore_data :- reconsult(passenger_data).
  • Add these as goals before the repeat and after the COMMAND=quit in main/0
  • Change travel project properties to exclude passenger_data.pro from builds.
  • Create an initial passenger_data.pro file in the project with the single clause: current_id(1000).