Re: spurious space after macro expansion in math mode for TeX output

[Gavin Smith]

On Mon, Nov 07, 2022 at 04:08:54PM +0100, Vincent Lefevre wrote:
> Consider the following test.texi file:
> 
> ------------------------------------------------------------
> \input texinfo    @c -*-texinfo-*-
> 
> @tex
> \gdef\atan{\mathop{\rm atan}}
> @end tex
> 
> @ifnottex
> @macro atan
> atan
> @end macro
> @end ifnottex
> 
> @node Top
> @node Test
> 
> Spacing test with atan.
> 
> @math{@atan{}(x)}
> 
> @math{\atan(x)}
> 
> @bye
> ------------------------------------------------------------
> 
> and run "texi2dvi --pdf test.texi".
> 
> With \atan, everything is fine. But with @atan{}, I get a spurious
> space between "atan" and "(x)" in the generated PDF, though the
> result should be identical to \atan.

This is not actually a Texinfo problem, as you are not using
a Texinfo macro, but a TeX macro.  The same output difference
would occur even without macros.

I suspect the braces are affecting the spacing in math mode.  The
empty {} is treated as a symbol.

You may remove the braces thusly:

@tex
\gdef\atan#1{\mathop{\rm atan}}
@end tex

See how the #1 parameter will absorb the empty braces.  With this
definition, @atan{} must be used, not just @atan (without braces).