[SOLVED] CS % Valid locations. locations/1

% Valid locations. locations/1

location(great_hall).
location(ophelia_bedroom).
location(polonius_bedroom).
location(courtyard).
location(chapel).
location(castle_wall).

% Valid characters. characters/1
character(ophelia).
character(polonius).
character(gertrude).
character(claudius).
character(hamlet).

% The current location of characters and objects. in_location/2
:- dynamic(in_location/2).

in_location(ophelia, great_hall).
in_location(polonius, great_hall).
in_location(hamlet, chapel).

% Valid story events. story_event/1.
story_event(polonius_scold_ophelia).
story_event(claudius_confesses_murder).

% Story events that have already occurred. event_occurred/1.
:- dynamic(event_occurred/1).

event_occurred(claudius_confesses_murder).

% Availability tests for story events (scenes). event_available/1.

event_available(polonius_scold_ophelia) :-
+( event_occurred(polonius_scold_ophelia) ),
in_location(ophelia, Loc),
in_location(polonius, Loc),
+( character_present(Loc, [ophelia, polonius]) ).

% load the lists module since were using the member/2 predicate
:- use_module(library(lists)).

% True if a character is present in a location who is not in the list of excluded characters.
character_present(Location, ExcludedChars) :-
in_location(Char, Location),
+( member(Char, ExcludedChars) ).

% Moving a character to a location.
move(Char, NewLoc) :-
in_location(Char, CurrentLoc),
location(NewLoc),
CurrentLoc = NewLoc,
retract( in_location(Char, CurrentLoc) ),
asserta( in_location(Char, NewLoc) ).