oop

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% library

use_module(library(assoc)).

proto((N, Slots), C, P) :- call(P, (H, Slots)), append([C], H, N).

root(([root], Slots)) :- empty_assoc(Slots).

add_attr((H, S), A, V, (H,N)) :- put_assoc(A, S, V, N).

set_attr(O, A, V, N) :-  add_attr(O, A, V, N).

get_attr((_, Slots), A, V) :- get_assoc(A, Slots, V).

isa(([C|_], _), C).
isa(([_|Cs],_), C) :- isa((Cs,_), C).

classof(([C|_],_), C).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% usage

grand_parent(P) :- proto(P0, grand_parent, root),
    add_attr(P0, attr0, initial_value, P).

parent(P) :- proto(P0, parent, grand_parent),
    add_attr(P0, answer, 42, P).

son(P) :- proto(P0, son, parent),
    add_attr(P0, weight, 1, P).

new_son(P) :- son(P0), set_attr(P0, answer, 0, P).