Re: Simplify define-markup-[list-]command-internal, (issue 545590045 by address@hidden)

[Han-Wen Nienhuys]

On Sun, Feb 16, 2020 at 10:40 PM David Kastrup <address@hidden> wrote:

> >> > In this commit, extra support for the case where command-and-args is
> >> empty was added, ie.
> >>
> >> That characterisation is completely wrong.  The support is not for the
> >> cases "where command-and-args is empty" but rather where
> >> command-and-args is not a list but a single symbol.  Just like
> >>
> >> (define symbol value)
> >> and
> >> (define (symbol arg1 arg2) body...)
> >>
> >
> > I'm trying to get the markup macros working with GUILE 2.x compilation,
> > which means that all calls to module-define! have to go.
> >
> > As a prelude to that, I'm trying to understand what this code is trying
> to
> > do.
> >
> > I don't think supporting
> >
> >   (define-markup-command sym1 sym2)
> >
> > is very useful, but if you really want to have this, it should be
> > documented and tested.
>
> It is not as much (define-markup-command sym1 sym2) rather than
>
> (define-markup-command sym1 (markup-lambda (...))
>
> where the markup-lambda expression is independently created.
>
> This was supposed to be the implementation used in parser.yy for things
> like
>
> \markup big-red = \markup \big \with-color #red \etc
>
> where defined name and definition are separate entities.  It turned out
> that calling macros from C did not work well, so I instead I had to call
> the non-macro internals.  It still made no sense scrapping that
> functionality since it is similarly useful from Scheme where it looks
> decidedly more natural than using the internals.
>
> It would appear I am not alone in considering that useful:
>
> git blame d03a3486639de982cfb6c6c315d76039bc5a0ac5 ly/markup-init.ly
>
> shows Nicolas Sceaux already implementing this ability independently in
> 2006.
>

I'll take the blame for not having reviewed it carefully enough. This
functionality was undocumented and untested in 2006, and I bet that I
didn't understand it back then. I had a hard time keeping up with Nicolas'
mastery of Scheme macros.

I propose that if we keep it, it gets commented, documented and tested.
Could you propose change to do so?

-- 
Han-Wen Nienhuys - address@hidden - http://www.xs4all.nl/~hanwen