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Re: Comment period extended for Unicode's changing some commoncharacters from Punctuation to Symbol

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From:
Nicholas Clark
Date:
February 5, 2013 14:20
Subject:
Re: Comment period extended for Unicode's changing some commoncharacters from Punctuation to Symbol
Message ID:
20130205142017.GN5653@plum.flirble.org
On Thu, Nov 29, 2012 at 07:21:45PM -0500, David Golden wrote:
> On Thu, Nov 29, 2012 at 12:58 PM, Leon Timmermans <fawaka@gmail.com> wrote:
> >> * How can we let programs introspect the version of Unicode that Perl provides?

> >> * Is it possible to make any of this pluggable, so a program could
> >> specify which version of Unicode classes they want to use?
> >
> > How do you scope that? Specially with things like qr//.
> 
> I was thinking globally for the interpreter.  "Run 5.16, but still use
> the Unicode 5.X char classes".  But as Karl points out, it's a no-go.
> It's another exception in the idea that "use v5.14" means you should
> get Perl v5.14 semantics when running later Perls.

I had been of the view that if we had the resources (which we don't),
regular expressions (at least) are viable to split the compilation, from
the runtime.

But the more I get to see the regular expression engine code, and the more
I think about it, I really think that it's impossible to meaningfully
offer previous-version semantics, even in the regular expression engine.

The implementation of the runtime is just too tightly coupled to the
implementation of the compiler. Just like the main interpreter. The
runtime doesn't have a nice abstracted, documented, tested, (mostly)
unchanging interface which it guarantees to its end user. Hence you can't
decouple the compile-time from one version, and mate it to the runtime
from another version, and have it work.

There isn't a nice clean well-specified VM sitting at the heart of things.
However much we would like it to be otherwise.

Nicholas Clark

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