pack([],[]).
pack([H], [[H]]).
pack([H,H|T], R) :- append([H], T, L), pack(L, [X|Y]),
                    append([H], X, P), append([P], Y, R).
pack([H|T], R):- pack(T, L), append([H], L, R).

?- pack([1,1,2,2,1,1,1,3],R).
R = [[1|1], [2|2], [1, 1|1], [3]]