navigation tree with prolog

navigation.pl

child(n1, [n11, n12]).
child(n11, [c11, c2]).
child(n12, [c11]).
child(c1, [c11, c12]).
child(c11, [p111, p112]).
child(c12, [p112]).


% distributive
is_child(A, B) :- child(A,KIDS), member(B, KIDS).
% transitive
is_child(A, C) :- is_child(A,B), is_child(B,C).

% upwards
is_root(A, _root) :- parents(A, P), length(P, L), L = 0 -> _root = true ; _root = false.
parents(A, _parents) :- findall(_parents, (child(_parents, B), member(A, B)), _parents).
parent(A, _parent) :- parents(A, P), nth1(1, P, _parent, _).
path_to_root(A, _path) :- 
	is_root(A, _root), _root -> 
	_path = A;
	parent(A,B), path_to_root(B, C), append([A], C, _path).

% downwards
children(A, _children) :- findall(Y, child(A, Y), Y), flatten(Y, _children).
%% pre-order
tree(A, _tree) :- 
	children(A, B),
	maplist(tree, B, C),
	append([A], C, _tree).