[texhax] Delimited arguments and ProvidesFile macro in hyphen.cfg

[Heiko Oberdiek]

On Mon, Jan 02, 2012 at 06:13:30PM -0700, Doug McKenna wrote:

> \def\ProvidesFile#1[#2 #3 #4]{\toks 8{Babel <#3> and hyphenation patterns 

> \ProvidesFile #1[#2 #3 #4]->\toks 8{Babel <#3> and hyphenation patterns 
> for }\b
> bl at tempa #1[#2 #3 #4]\let \ProvidesFile \bbl at tempa 
> #1<-{hyphen.cfg} 
> #2<-2008/07/06
> #3<-v3.8l
> #4<-Babel language switching mechanism
> {\toks}
> etc.
> 
> My question is, why does the argument token list for parameter #1 include 
> the open and closed braces (followed by a space)?  I thought TeX stripped 
> the outermost set of braces during argument collection.

Because of the space, hyphen.cfg installed on my system
contains:

  \ProvidesFile{hyphen.cfg}
                  [2008/07/08 v3.8m %

The first argument of the definition above is a delimited
argument, delimited by "[". In this case this is
"{hyphen.cfg}" and the line end that becomes a space: "{hyphen.cfg} ".
Now the braces are not a pair of outermost braces and are not
removed.

> The reason I'm confused is because if I trace the following simple test 
> macro with parallel argument delimiter structure
> 
> {
> 	\def\tester#1[#2 #3 #4]{}
> 	\tracingcommands=3
> 	\tracingmacros=3
> 	\tester{sweet}[babel onion tears]%
> }
> 
> during a normal run of TeX (using the LaTeX format), the log file contains
> 
> \tester #1[#2 #3 #4]->
> #1<-sweet
> #2<-babel
> #3<-onion
> #4<-tears
> 
> and the first argument has had its outermost braces stripped, as I 
> expected.

Compare with "\tester{sweet} [babel onion tears]".

Yours sincerely
  Heiko Oberdiek