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Re: Define variable only if it doesn't exist / is unbound
From: |
Thomas Morley |
Subject: |
Re: Define variable only if it doesn't exist / is unbound |
Date: |
Thu, 28 Mar 2019 23:14:52 +0100 |
Am Do., 28. März 2019 um 22:22 Uhr schrieb Aaron Hill
<address@hidden>:
>
> On 2019-03-28 2:18 pm, Valentin Villenave wrote:
> > On 3/28/19, Pedro Pessoa <address@hidden> wrote:
> >> I imagined something like:
> >>
> >> %%% pseudo
> >> #(define var
> >> (not (is-bound? var) 0))
> >> %%%
> >
> > I’d probably probably do something like
> >
> > (null? (ly:parser-lookup 'var))
> >
> > But I’m sure there are better ways :-)
>
> ;;;;
> (if (not (defined? 'foo)) (define foo 47))
> ;;;;
>
>
> -- Aaron Hill
It's worth mentioning, the above will throw an error in guilev2:
error: GUILE signaled an error for the expression beginning here
#
(if (not (defined? 'foo)) (define foo 47))
definition in expression context, where definitions are not allowed
Probably better get used to below:
#(if (not (defined? 'foo)) (ly:parser-define! 'foo 47))
Cheers,
Harm
- Define variable only if it doesn't exist / is unbound, Pedro Pessoa, 2019/03/28
- Re: Define variable only if it doesn't exist / is unbound, Valentin Villenave, 2019/03/28
- Re: Define variable only if it doesn't exist / is unbound, Aaron Hill, 2019/03/28
- Re: Define variable only if it doesn't exist / is unbound,
Thomas Morley <=
- Re: Define variable only if it doesn't exist / is unbound, Aaron Hill, 2019/03/28
- Re: Define variable only if it doesn't exist / is unbound, Richard Shann, 2019/03/29
- Re: Define variable only if it doesn't exist / is unbound, Thomas Morley, 2019/03/29
- Re: Define variable only if it doesn't exist / is unbound, Aaron Hill, 2019/03/29
- Re: Define variable only if it doesn't exist / is unbound, Thomas Morley, 2019/03/29
- Re: Define variable only if it doesn't exist / is unbound, Thomas Morley, 2019/03/29
- Re: Define variable only if it doesn't exist / is unbound, Vaughan McAlley, 2019/03/30
Re: Define variable only if it doesn't exist / is unbound, Pedro Pessoa, 2019/03/28
Re: Define variable only if it doesn't exist / is unbound, David Kastrup, 2019/03/29