As Erlang is Turing-complete, obviously you can code FSM in it. The question is, giving Erlang/OTP Soft-Realtime Telecom roots, why FSM primitives are so weak?

From a good FSM library I would expect following:

  1. Specify human readable STT (State Transition Table)
  2. For each event/state combination specify if it's valid or should be ignored, etc.
  3. On entry / on exit for each state.
  4. Masking/unmasking of events.

gen_fsm as it today do not provide much value over gen_server.