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Re: Detecting null markup in Scheme
From: |
David Kastrup |
Subject: |
Re: Detecting null markup in Scheme |
Date: |
Fri, 01 Sep 2017 19:06:21 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.0.50 (gnu/linux) |
Graham King <address@hidden> writes:
> I have a monstrous music-function that constructs a markup in Scheme and
> then decides whether to put it at system-level or staff-level, along the
> following lines (much-redacted):
>
> foo = #(define-music-function (args...) (types...)
> (let* ((markupContents #{
> \markup {
> \concat {
> #markupOne
> #markupTwo
> }}
> #})
> (case whereMarkup
> ((system) #{ \mark #markupContents #})
> ((staff) #{ <>^ #markupContents #})
> (else #{ \mark \markup \color #red #markupContents #})
> ))
> )
>
> The problem is: how best to deal with the case where #markone and
> #markuptwo are both empty, i.e. #{ \markup "" #}, and no markup at all
> should be attempted?
>
> I've tried variations on:
> ( if ( string=? ( markup->string markupContents )
> ( markup->string empty-markup ))
> (#{ <> #})
> (case whereMarkup ...
>
> but my grasp of Scheme, never very firm, is slipping away.
>
> Grateful for any suggestions, pointers to documentation/tutorials,
> etc.
I'd just try (equal? markupContents "") here. equal? can compare any
objects for "equality", and at least "" as input should compare equal
then.
--
David Kastrup