Obtain Source (Sink) out of Source (Sink) and f:A->B

[Salva Alcántara]

If I have a Source<A> (Sink<A>), what would be the simplest way of
obtaining a Source<B> (Sink<B>) based on a mapping/conversion function from
A to B. AFAIK sources & sinks don't have map so I was just wondering how to
approach this in the context of new sources/sinks apis.

Regards,

Salva