Callbacks from modules

[Ivan Andrus]

I’ve started writing an Emacs module to access NSSpeechSynthesizer on OS X (and 
maybe GNUStep though I haven’t tested it there).  I’ve been using the mod-test 
module as an example and I have it working reasonably well except that I don’t 
have any idea how to run a callback.

When the synthesizer is done speaking it sends an Objective-C message 
speechSynthesizer:didFinishSpeaking.  From there I would like to run an elisp 
hook, say `ns-speech-finished-speaking-hook`.  How can I do this?  Do I have to 
squirrel away a pointer to an emacs_env somehow?  I tried naively storing env 
from a previous call but, not surprisingly, the pointer is invalid when I try 
to use it.

Thanks,
Ivan