lab2.prolog

children(Parent,L) :- findall(Next,parent(Parent,Next),L).
ancestors(Child,L) :- findall(Next,parent(Next,Child),L).

repr_internal(Elem,L,R) :- (L == [] -> ancestors(Elem,R); children(Elem,R)).
repr_retval(Elem,R) :- children(Elem,L), repr_internal(Elem,L,R).
repr(Elem):- repr_retval(Elem,R), write(R).

read_line_pls(L) :- read_line(X),string_to_atom(X,L).

main :-
  nl,
	write('Choose action:\n'),
	write('1. save current state\n'),
	write('2. find element\n'),
	write('3. add element\n'),
	write('4. remove element\n'),
	write('5. exit\n'),
	write('>>> '),	
	readln([X]),
	switch(X) ; main.

switch(1):- qsave_program('lab2.out',[class(development),op(save),autoload(true),goal(init)]), main.

switch(2):- write('Type element\'s name: '), read_line_pls(A), repr(A),nl, main.

switch(3):- write('Type parent\'s name: '), read_line_pls(P),
			write('Type child\'s name: '), read_line_pls(C),
			assert(parent(P,C)), main.

switch(4):- write('Type element\'s name: '), read_line_pls(A), retract(parent(_,A)), main.
	
switch(5):-	write('Bye.\n'), halt, halt.

init :- [library(http/dcg_basics),library(dialect/sicstus)], consult('cityes.pl'), main.