-module(rosetta). -compile(export_all). test() -> rosetta("ZYEEEEEABBCCCDDDDF"). rosetta([H|T]) -> rosetta([], [H], T). rosetta(L, [H|_]=Act, [H|T1]) -> rosetta(L, [H|Act], T1); rosetta(L, Act, [H|T]) -> rosetta([Act|L], [H], T); rosetta(L, Act, []) -> lists:reverse([Act|L]).