Port/Stream from Cell is Unsafe

declare L SEND={NewSend L} in

{Inspect L}

%% ill-behaved reader of L writes to L unauthorized
L=f(_)|f(b)|_

{SEND f(a)}     %% succeeds because f(a) unifies with f(_)
{SEND f(a)}     %% fails because f(a) doesn't unify with f(b)

• this abstraction isn't safe because SEND does not have exclusive write permission to the stream
• anybody can instantiate the stream and thus break the abstraction