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Re: [Patch] hard-widen-limits [was Re: Syntax tables for multiple modes

From: Stefan Monnier
Subject: Re: [Patch] hard-widen-limits [was Re: Syntax tables for multiple modes [was: bug#22983: syntax-ppss returns wrong result.]]
Date: Sat, 30 Apr 2016 10:06:51 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1.50 (gnu/linux)

> Stefan, adding extra argument turned to be a train wreck. I am afraid, if I
> cannot get help on how to extend primitives, I am giving up at this point.

Indeed, I didn't consider the fact that some (most?) of those functions
are also implemented as bytecode.  Hmm...

>       case (Bbobp):
> -       PUSH (Fbobp ());
> +       TOP = Fbobp (TOP);
>         NEXT;
You can't change the bytecode's behavior since existing .elc files will
otherwise break down completely since the stack's will be modified in
a way it doesn't expect [ For new .elc files you could make it work by
changing bytecomp.el to update the byte compiler's understanding of how
the bytecode works.  ]

So for functions that have a corresponding bytecode, you can either stop
using the bytecode when the new arg is used (this requires changing
bytecomp.el accordingly, e.g. by removing the corresponding code such as
"(byte-defop 125 -1 byte-narrow-to-region)"), or you leave the function
unchanged and introduce another function instead.

Having a bytecode for `narrow-to-region` is not very useful (the
main/only benefit is speed of executing narrow-to-region, but the
difference shouldn't be significant) so it'd be perfectly OK to stop
using this bytecode.  For `bobp` I'm not completely sure of the
potential performance impact, OTOH.


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