[erlang-questions] Why does this compile without warnings/errors?

[Yves S. Garret]

I'm looking at this code:

loop(ExoSelf_PId) ->
  receive
    {ExoSelf_PId, {Id, Cx_PId, ActuatorName, Fanin_PIds}} ->
      loop(Id, Cx_PId, ActuatorName, {Fanin_PIds, Fanin_PIds}, [])
  end.

Now, what I'm not quite 'getting' is why the compiler is not complaining
about
ExoSelf_PId.  First of all, it's not used anywhere.  Second of all, if it's
used, it's
used to bind (to an already bound) variable and that's the message that's
received
to this process.  If I were to pass in Foo and then do Foo = 5, the
compiler would
tell me that that is impossible, so what is different in this case?
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