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Re: Purpose of SRFI 39

This page is part of the web mail archives of SRFI 39 from before July 7th, 2015. The new archives for SRFI 39 contain all messages, not just those from before July 7th, 2015.

>>>>> "Marc" == Marc Feeley <feeley@xxxxxxxxxxxxxxxx> writes:

Marc> I agree that the API of parameters is not abstract, and that this
Marc> could be improved with separate procedures (or syntax) for creation,
Marc> mutation, reading and binding of dynamic variables.  I did not propose
Marc> this because of the convergence by many implementations to the
Marc> "parameters" API and I wanted to place minimal burden on
Marc> implementors/users of this API.  Moreover, the main point of SRFI 39
Marc> is to propose the "right" semantics for dynamic binding in the
Marc> presence of threads.

But it seems you can't have both at the same time: you think that the
"right" semantics is precisely not the semantics the implementations
are converging on.  You're therefore creating a confusing situation:
the API (and the sheer presence) suggests that the parameter APIs are
the same when they're not.

Marc> I strongly believe that MzScheme's way (mutation without sharing) is
Marc> wrong.  It prevents a thread T1 from invoking a continuation C that
Marc> was created in another thread T2, because T1 can't reinstate C's
Marc> dynamic environment properly.  The only way this can work in the
Marc> presence of mutable dynamic variables is if it is possible for
Marc> different threads to share the dynamic environment.  This is what
Marc> I'm proposing.

That's fine with me.  However, if you're departing from prior practice
in this way (and distinguishing MAKE-MUTABLE-PARAMETER from
MAKE-PARAMETER doesn't really affect the issue) and thus changing the
previously established API, why not make this clear by introducing a
new API with the proper abstractions?  This way, there can be no

Moreover, I doubt that this is a significant burden on the
implementors (at least not if the current draft is not already a
significant burden).  If anything, the burden is with the *users* with
code using the old API.  But for them, it's easy enough to create a
parameter library with the right semantics for their programs.

Cheers =8-} Mike
Friede, Völkerverständigung und überhaupt blabla