Erlang is based on the ACTOR model, not CSP. The main practical differences between Erlang and CSP is that Erlang uses asynchronous dynamically-typed messages sent to a particular address (process id), whereas CSP systems usually deal with synchronous messages sent down a particular, typed channel. But they are both message-passing systems with the idea of removing shared mutable data, as you say. For an implementation of CSP in the pure functional language Haskell, see my library CHP (http://www.cs.kent.ac.uk/projects/ofa/chp/).