Re: thin_space causes collateral damage in eqn

[Damian McGuckin]

Doug, Branden,

On Tue, 16 May 2023, Douglas McIlroy wrote (but in not the same order)

> Apparently thin_space serves double duty--to control automatic spacing
> and to set the width of ^.

> This coupling of function strikes me as a bug. One thinks of ^ and ~
> as groff keywords, not characters. And even if they are characters,
> they represent white space placed deliberately, not "automatically
> inserted".

I would agree with Doug 100%

> Another parameter, thick_space, has the same effect on ~.

There is also 'medium space' but it corresponds to nothing explicit or 
deliberate as far as can see.

The documentation says that *_space are only for automatic spacing.

I actually cannot see where the meaning of either '~' or '^' is defined in 
the GNU eqn(1) manual page. But maybe my eyes are getting old. Or I should 
consider Branden's comment and take that as a delta against some implied 
expert's understanding of EQN. Sadly I am not an expert yet because I am 
still learning things about EQN after 40 years.

I note that the Plan 9 eqn(1) man page says

        "Tokens within eqn are separated by spaces, tabs, newlines,
        braces, double quotes, tildes or circumflexes. Braces {} are used
        for grouping; generally speaking, anywhere a single character like
        x could appear, a complicated construction enclosed in braces may
        be used instead. Tilde ~ represents a full space in the output,
        circumflex ^ half as much."

Maybe text along those lines needs to go into GNU eqn's man page.

One can argue that there needs to be

        thin_space_user
        thick_space_user

if control is needed over those for the user's deliberately defined cases.

That said, they should be called

        full_space_user
        half_space_user

because that is what they technically are. We could just drop the '_user' 
and note in the documentation that they are explicitly/deliberately forced 
into the said equation by '~' and '^' respectively.

My 2c - Damian

P.S. Sadly Lorinda Cherry passed away a bit over 12 months ago.