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Message-ID:  <FCD36D2B-F401-4704-9FDD-80204B5FA03D@gmail.com>
Date:         Thu, 6 Nov 2008 19:04:47 +1030
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From: Will Robertson <wspr81@GMAIL.COM>
Subject: Some implementation details of \let:XX
To: LATEX-L@LISTSERV.UNI-HEIDELBERG.DE
Precedence: list
Status: R

Hello,

Taking a look at how \let:NN and friends are implemented strongly  
tempted my "clean up" urge. Rather than delay it for the "big future  
refactor" that's going to happen at some stage, I thought it small  
enough to address immediately.

(Also, I'm using this public list since I'm not entirely sure that  
conducting the expl3 business "in the dark" isn't one of the reasons  
that the project has attracted less interest than we possibly would  
have liked.)

Here's the offending code:

\def_protected_long_new:Npn \let:NN #1{\let:NwN #1=~}
\def_new:Npn\let:cN #1 {\exp_after:NN\let:NN\cs:w#1\cs_end:}
\def_new:Npn\let:Nc{\exp_args:NNc\let:NN}
\def_new:Npn\let:cc{\exp_args:Ncc\let:NN}

Yielding concerns:
  - Why is \let:NN long?
  - Shouldn't the variants be protected as well?
  - I'd be surprised if \let:cN *really* needs to be hand-optimised,  
given the definition of \exp_args:Nc :

     \def_long_new:Npn \exp_args:Nc #1#2{\exp_after:NN#1\cs:w#2\cs_end:}

I'd like to propose this change:

\def_protected_new:Npn \let:NN #1 { \let:NwN #1=~ }
\def_protected_new:Npn \let:cN { \exp_args:Nc  \let:NN }
\def_protected_new:Npn \let:Nc { \exp_args:NNc \let:NN }
\def_protected_new:Npn \let:cc { \exp_args:Ncc \let:NN }

Any comments?

Cheers,
Will