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Re: non-local exits are icky



Thank you.   

I'd like to take this (the non-local exit) issue up -- but I _think_
that will be far easier if we first fix the calling conventions.

Better non-local exit handling gives additional excuses for changing
the calling conventions -- so maybe we should take this up now.

But on the other hand, we have plenty of reasons for new calling
conventions already -- and once we pick the Pika conventions ( :-), 
better solutions for non-local exits will be pretty easy to motivate.

-t






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    > 
    > >>>>> "Tom" == Tom Lord <lord@xxxxxxx> writes:
    > 
    > Tom> To test my understanding, and before replying to the proposal further,
    > Tom> let me just say back to you two things that I think you would agree
    > Tom> with (and think are obviously true):
    > 
    > Tom> 1) Non-local exits to upward continuations currently afford no
    > Tom>    general mechanism for cleanups in FFI-using C.
    > 
    > Yes.
    > 
    > Tom>    Later SRFIs will have to add
    > Tom>    additional mechanisms to the FFI to handle such situations.
    > 
    > Yes, provided that they are necessary.  I'm not convinced they are,
    > but that's irrelevant here.
    > 
    > Tom> 2) The specification of error signalling could be made clearer:
    > 
    > That's probably true.
    > 
    > Tom>    but is could say something more like:
    > 
    > Tom>         The following macros explicitly signal certain errors.
    > Tom>         If an error is signalled, either: [...]
    > 
    > That's arguable, but not what I intended.  What I intended was that
    > the "an error is signalled" means the same thing as in R5RS, whatever
    > that is for a given Scheme implementation.  In particular, what you
    > propose ...
    > 
    > Tom>           1) the computation must be terminated
    > 
    > Tom>           2) the computation may be continued in part by invoking
    > Tom>              a continuation which is upwards relative to the 
    > Tom>              C call that triggered the error.  (see "Calling Scheme
    > Tom>              procedures from C".)
    > 
    > ... seems to leave as much room for interpretation as what's in there now.
    > 
    > -- 
    > Cheers =8-} Mike
    > Friede, V?ölkerverst?ändigung und ?überhaupt blabla
    > 
    > 
    >