You could do so, several different ways, e.g.:
(1) use the process dictionary,
(2) store data transparently to the new language’s user in ets (or, similarly, dets/mnesia),
(3) use separate (again, hidden from the language user) Erlang processes for mutable cells.
You can't get hig-performance mutability, but you can definitely implement a language with mutability on BEAM.
You could do so, several different ways, e.g.:
(1) use the process dictionary,
(2) store data transparently to the new language’s user in ets (or, similarly, dets/mnesia),
(3) use separate (again, hidden from the language user) Erlang processes for mutable cells.
You can't get hig-performance mutability, but you can definitely implement a language with mutability on BEAM.