Re: incorrect @math spacing for PDF output with an empty macro

[Vincent Lefevre]

On 2022-10-16 12:18:51 +0100, Gavin Smith wrote:
> On Sat, Oct 15, 2022 at 12:40:32PM +0200, Vincent Lefevre wrote:
> > The spaces in math mode can normally stretch and shrink (not in
> > the same way as outside of math mode, though). But there are some
> > TeX commands that changes spaces to fixed spaces in math mode.
> > I just wanted to be sure that @w did not change anything in this
> > respect.
> 
> The answer is I do not know, although I don't expect there would be
> a problem.

@w doesn't work correctly in math mode:

------------------------------------------------------------
\input texinfo    @c -*-texinfo-*-
@documentencoding UTF-8

@node Top
@node Test

Formatting test.

zzzzzzzzzzzzzzzzzz @math{a + b}
zzzzzzzzzzzzzzzzzz @math{a + b}
zzzzzzzzzzzzzzzzzz @math{a + b}
zzzzzzzzzzzzzzzzzz @math{a + b}
zzzzzzzzzzzzzzzzzz @math{a + b}
zzzzzzzzzzzzzzzzzz @math{a + b}
zzzzzzzzzzzzzzzzzz @math{a + b}
zzzzzzzzzzzzzzzzzz @math{a + b}

zzzzzzzzzzzzzzzzzz @w{@math{a + b}}
zzzzzzzzzzzzzzzzzz @w{@math{a + b}}
zzzzzzzzzzzzzzzzzz @w{@math{a + b}}
zzzzzzzzzzzzzzzzzz @w{@math{a + b}}
zzzzzzzzzzzzzzzzzz @w{@math{a + b}}
zzzzzzzzzzzzzzzzzz @w{@math{a + b}}
zzzzzzzzzzzzzzzzzz @w{@math{a + b}}
zzzzzzzzzzzzzzzzzz @w{@math{a + b}}

@bye
------------------------------------------------------------

One can see that with @w, spaces do not stretch.

However, a solution is to define a macro with @iftex and @ifnottex
so that @w is not used for TeX. Basically, @math{T} for TeX, @w{T}
otherwise. (I recall that the goal is to use that when T is a very
simple math expression, so that it is OK for Info and HTML without
any special handling.)

For instance:

------------------------------------------------------------
\input texinfo    @c -*-texinfo-*-
@documentencoding UTF-8

@iftex
@macro m {T}
@math{\T\}
@end macro
@end iftex

@ifnottex
@macro m {T}
@w{\T\}
@end macro
@end ifnottex

@node Top
@node Test

Formatting test.

zzzzzzzzzzzzzzzzzz @m{a + b}
zzzzzzzzzzzzzzzzzz @m{a + b}
zzzzzzzzzzzzzzzzzz @m{a + b}
zzzzzzzzzzzzzzzzzz @m{a + b}
zzzzzzzzzzzzzzzzzz @m{a + b}
zzzzzzzzzzzzzzzzzz @m{a + b}
zzzzzzzzzzzzzzzzzz @m{a + b}
zzzzzzzzzzzzzzzzzz @m{a + b}

@bye
------------------------------------------------------------

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)