Re: Scheme pattern for retrieving data in objects

[Han-Wen Nienhuys]

On Fri, Apr 1, 2022 at 6:43 PM Jean Abou Samra <jean@abou-samra.fr> wrote:
>
> Folks,
>
> Just a random thought in passing: I just wrote something of this kind
> once again:
>
> (let ((elements (ly:music-property m 'elements))
>        (element (ly:music-property m 'element))
>        (articulations (ly:music-property m 'articulations)))
>    ...)
>
> (let ((padding (assoc-ref details 'padding))
>        (common-Y (assoc-ref details 'common-Y)))
>    ...)
>
> (let ((padding (ly:grob-property grob 'padding)
>        (shorten-pair (ly:grob-property grob 'shorten-pair))
>        (normalized-endpoints (ly:grob-property grob 'normalized-endpoints)))
>    ...)
>
>
> Does anyone find a value in defining a macro for this?
>
>
> \version "2.23.8"
>
> #(define-syntax-rule (fetch obj getter (sym ...) body body* ...)
>     (let ((evald-obj obj)
>           (evald-getter getter))
>       (let ((sym (getter obj 'sym))
>             ...)
>         body body* ...)))
> {
>    c'1
>    \tweak after-line-breaking
>      #(lambda (grob)
>         (fetch grob ly:grob-property (left-bound-info)
>           (fetch left-bound-info assoc-ref (common-Y X padding attach-dir)
>             (ly:message "common-Y=~a X=~a padding=~a attach-dir=~a"
> common-Y X padding attach-dir))))
>    \startTextSpan
>    c'1\stopTextSpan
> }

It's shorter, but is it easier to understand and discover? Is the
former code (which is somewhat verbose) a real barrier to getting
coding/typesetting done?

Over the years, I've become extremely wary of syntactic sugar: it adds
an extra barrier to usage/development because everyone not only has to
learn Scheme, they also have to learn the (lilypond specific) idioms
involved.

-- 
Han-Wen Nienhuys - hanwenn@gmail.com - http://www.xs4all.nl/~hanwen