Re: pure-fns in byte-opt.el

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 29 Jul 2017 12:34:46 -0400
> From: Mark Oteiza <mvoteiza@udel.edu>
> Cc: emacs-devel@gnu.org
> 
> >So I think the problem happens in unidata-word-list-compress, and it
> >happens because make-vector, which that function calls always returns
> >the same vector, so the vectors used by that function and created by
> >it are all messed up.
> 
> I don't follow: why does it always return the same vector?

That's how I understand what the byte compiler does when you declare
that function "pure".

> That
> particular call to make-vector should be unaffected by make-vector being
> marked pure, because its arguments aren't constants.

Sorry, I meant the make-vector call in unidata-gen-table-word-list,
whose result is passed to unidata-word-list-compress.

> OTOH, the form
> (make-vector 128 nil) would indeed get byte-compiled into the constant
> [nil nil … nil]

The problem, I think, is not with a single call, but with that call
being in a loop, and the code expects each iteration to produce a new
vector.