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Re: Macro to prepend element to list


From: Linus Björnstam
Subject: Re: Macro to prepend element to list
Date: Sat, 20 Mar 2021 17:04:56 +0100
User-agent: Cyrus-JMAP/3.5.0-alpha0-206-g078a48fda5-fm-20210226.001-g078a48fd

Well, mutating like that is not very common, except for maybe with alists.

In which situations are you mutating the list like that? Usually you would 
build a reverse list using a recursive function and an accumulator, which can 
be done without set! (which has a boxing overhead).

-- 
  Linus Björnstam

On Sat, 20 Mar 2021, at 15:24, Jean Abou Samra wrote:
> Hello,
> 
> I find myself frequently using the following macro:
> 
> (define-macro (prepend! thing lst)
>     `(set! ,lst (cons ,thing ,lst)))
> 
> Have I missed a module somewhere that does this kind of things?
> At least, I couldn't find anything in SRFIs. It may also be the
> case that this is too specific to certain non-functional usages
> (LilyPond in my case).
> 
> Thanks in advance,
> Jean Abou Samra
> 
> 
>



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