% P10 (*):  Run-length encoding of a list

% encode(L1,L2) :- the list L2 is obtained from the list L1 by run-length
%    encoding. Consecutive duplicates of elements are encoded as terms [N,E],
%    where N is the number of duplicates of the element E.
%    (list,list) (+,?)

:- ensure_loaded(p09).

encode(L1,L2) :- pack(L1,L), transform(L,L2).

transform([],[]).
transform([[X|Xs]|Ys],[[N,X]|Zs]) :- length([X|Xs],N), transform(Ys,Zs).