Reia isn't "interpreted" in any manner different from the Erlang language itself. It's somewhat similar to CoffeeScript in that it uses parse transforms to produce Erlang parse trees which are then compiled by the Erlang compiler just like any other Erlang source code. However, it's a bit more like JRuby in that it ships a runtime, core types, and a standard library.

It's slower than Erlang, not because it's executed in a different manner than Erlang, but because it supplies a separate late binding mechanism for dispatching methods to their receivers.