getUserReply(R):-
	readSentence(R).

readSentence(Words) :- get0(C),
                    read_rest(C,Words).
          
read_rest(46,['.']) :- !.
read_rest(63,['?']) :- !.

read_rest(C,Words) :- ( C=32 ; C=10 ) , !,
                     get0(C1),
                     read_rest(C1,Words).

read_rest(44,[','|Words]) :- !,
                             get0(C1),
                             read_rest(C1,Words).

read_rest(C,[Word|Words]) :- lower_case(C,LC), 
% we will need this because we concat_atoms and we will end up with variables unless we use lower case
                             read_word(LC,Chars,Next),
                             name(Word,Chars),
                             read_rest(Next,Words).

read_word(C,[],C) :- ( C=32 ; C=44 ; C=10 ;
                         C=46 ; C=63 ) , !.

read_word(C,[LC|Chars],Last) :- lower_case(C,LC),
                                get0(Next),
                                read_word(Next,Chars,Last).

lower_case(C,C) :- ( C <  65 ; C > 90 ) , !.
lower_case(C,LC) :- LC is C + 32.




/*
*
* default answers of the expert systems
* 1) no
* 2) yes
* 3) I understand
*
*/



:- op(100, xfx, 'is_a'). % this operator will be used to store data from the statements in the knowledge database
:- op(100, xfx, 'is_really'). % this operator will be used for evaluating the questions

Who is_a What :-
	%writeln('who = '),writeln(Who),
	%writeln('what= '),writeln(What),
	(	
		(is_list(Who)  -> concat_atom(Who,'_' ,K)  ; K=Who),
		(is_list(What) -> concat_atom(What,'_',V) ; V=Who)
	),
	Fact	=.. [fact,V,K],
	system_mode(on),
	redefine_system_predicate('$fact'(_,_)),
	dynamic('fact'/2),
	assertz(Fact).

Who is_really What:-% this where the question is evaluated and an answer in the form YES/NO is given
	writeln('who = '),writeln(Who),
	writeln('what= '),writeln(What),
	(	
		(is_list(Who)  -> concat_atom(Who,'_' ,K)  ; K=Who),
		(is_list(What) -> concat_atom(What,'_',V) ; V=What)
	),
	Fact	=.. [fact,K,V],

	Fact1	=.. [fact,K,X], % transitivity
	Fact2	=.. [fact,X,V],
	write('checking -> '),write(Fact),
	dynamic('fact'/2),
	(
		(
			(
				call(Fact) ; 
				( call(Fact1),call(Fact2),asserta(Fact) )%some memoization 
			),
			writeln('YES'),!,fail
		);
		writeln('NO'),!,fail
	).




s --> object(N,M) , [is] , [a] ,object(X,Y) , [.] ,{[N,M] is_a [X,Y]}.
s --> object(Who) , [is] , [a] ,object(X,Y) , [.] ,{Who is_a [X,Y]}.
s --> object(A,B) , [is] , det(_) , noun([Y]) , [of] , object(C,D) , [.] , { [A,B] is_a [Y,C,D] }.
s --> object(Who) , [is] , [a] ,object(What) , [.] ,{Who is_a What}.
s --> object(N,M) , [is] , [a] , level(X) , noun(Y),[.],{  [level,X] is_a [N,M] , write('last rule') }.
s --> [all] , num(X) , [courses] , [are] , adj([P]) , [courses] , [.] , { [P,course] is_a [level,X] }.

q --> [is] , object(N,M) , det(X) , adj([P]) , noun([Q]) , [?] , {  [N,M] is_really [P,Q]}.
q --> [does] , object(N,M) , [have] , [a] , noun([Q]) , [?] , { [Q,N,M] is_really H }.

object(X,Y) --> [X] , [Y] , { adj(X) , noun(Y) }.
object(X,Y) --> [X] , [Y] , { number(Y) }.
num(X) --> [X], { number(X) }.


object(X) --> [X].

det([X])	--> [X] , { det(X) }.
noun([X])	--> [X] , { noun(X) }.
adj([X])	--> [X] , { adj(X) }.

level(X) --> [X] , [level] , { number(X) }.

adj(advanced).
adj(basic).
adj(computing).
noun(course).
noun(courses).
noun(level).
verb(is).
verb(are).
verb(have).
det(the).
det(a).
det(an).
%number % predicate to be used when in need of numeral
noun(prerequisite).
pronoun(all).



%
% to end the conversation with the expert system use "end." 
%
% the system will write messages if what the user has written was a question or statement
% and it will reply nothing otherwise(error)
%


start:-
	repeat,
	getUserReply(X),
	write(X),
	(
	 (X =@= [ 'end','.' ] , !);
	 (last(X,'.'),s(X,[]),writeln('[I understand]'));
	 (last(X,'?'),q(X,[]))
	),
	fail.


%statement tests
test1:-
	s([com,400,is,a,computing,course,.],[]).
test2:-
	s([com,401,is,a,400,level,course,.],[]).
test3:-
	s([com,270,is,the,prerequisite,of,com,401,.],[]).
test4:-
	s([all,400,courses,are,advanced,courses,.],[]).


%question tests
test5:- 
	test1,
	q([is,com,401,an,advanced,course,?],[]).

test6:-
	test2,
	test4,
	q([is,com,401,an,advanced,course,?],[]).
test7:-
	test3,
	q([does,com,401,have,a,prerequisite,?],[]).