Message-ID: <51E6A798.3090503@morningstar2.co.uk>
Date: Wed, 17 Jul 2013 15:18:00 +0100
From: Joseph Wright <joseph.wright@morningstar2.co.uk>
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To: "latex-team@latex-project.org" <latex-team@latex-project.org>
Subject: Re: Michiel Helvensteijn's ideas
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On 17/07/2013 13:32, Will Robertson wrote:
> On 17/07/2013, at 9:53 PM, Joseph Wright <joseph.wright@morningstar2.co.uk> wrote:
> 
>> No, far too esoteric for me. We worked hard to cut down on the number of
>> arg types in the refactor, and I'm not sold on the idea of adding any
>> more back in.
> 
> Agreed. 
> 
> The one thing I've been keeping in the back of my mind is that as the number of functions that use \romannumeral increases the more justification there would be to reintroduce the "double" expansion arg spec. But I'm not sure if we're at the point yet (or if ever). 
> 
> W

The \romannumeral trick is not the same as the old "d" specifier, not
the triple ("e"?) one. Using \romannumeral ensures expansion in two
steps provided whatever is after the \romannumeral is
appropriately-designed. That's f-type expansion if you want to use it
via \exp_args:N..., but there are places it's handy to build directly
into code at the kernel level.

The old d-type was an \expandafter chain:

  \cs_new:Npn \exp_args:Nd #1#2
    {
      \exp_after:wN \exp_after:wN \exp_after:wN #1
        \exp_after:wN \exp_after:wN \exp_after:wN {#2}
    }

which is a very different thing as it only expands the first token in #2
(and the expansion of #2).

Joseph
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