Behaviour style question

[Attila Rajmund Nohl]

Hello!

I have a behaviour implemented by 6 modules. The functions of these
modules are called by an other module (let's call it manager module).
Then it turned out that one of the 6 modules needs a slightly
different interface than the other five, it needs an extra function.
Of course, the manager module has to be modified, there's a case
statement in the code.

My question is what to do with the behaviour? If I add the extra
function to the behaviour, I'll get compilation warnings in 5 modules
and that's generally a bad idea, because due to the these warnings I
might not notice more important warnings.

I can implement the extra function in all 5 modules like
get_alarm_type_data(_) ->
  erlang:error(this_should_not_be_called);

but I don't like this unnecessary code (I'd get a function_clause
without this and that's basically the same result) and I especially
don't like it in 5 files.

My gut feeling is that the 6th module with the extra function has a
different behaviour, so there should be a new behaviour for this
module (even if it's only implemented by one module). In this case I
should add to the documentation of the manager module that the Module
parameter to its functions must implement either the original or the
"extended" behaviour.

Any other ideas?