[texhax] FW: Re: Implementing control sequences with key values

[Uwe Lueck]

Correcting my 14.11.2010 19:02:33:
>> Wolfgang Schuster wrote:
>> > \def\direction#1=#2#3
>> >    {\def\currentdirection{#2#3}}
I commented:
> Wolfgang's code is redundant both in the definition and testing. 
> The core of his idea is:
>    \def\direction=#1 {\def\currentdirection{#1}}

But 

    \def\direction=#1#2 {\def\currentdirection{#1#2}}

is superior in allowing ("optional"!) spaces after "=" 
in using \direction.

>Selon "Philip Taylor (Webmaster, Ret'd)" :
>> 11/10 for effort, Wolfgang, but there are some common cases
>> for which it does not work :
>>
>> \direction = LTR\relax Direction: \currentdirection\par
>> \direction = RTL\relax Direction: \currentdirection\par
>>
>> \vskip\baselineskip
>>
>> \direction = LTR%
>> Direction: \currentdirection\par
>> \direction = RTL%
>> Direction: \currentdirection\par
I commented:
> The problem (noted by Paul and Phil) is that it is somewhat difficult with TeX 
> to catch a "parameter word" with varying "word" delimiters. Wolfgang chose 
> delimiters "=" and " ", which of course fails when " " is replaced by anything else. 

But one might say that " " is the best choice for the right delimiter, 
and the documentation may say that a space as right delimiter 
is required, so its your fault if you try another one. 
(TeXbook somewhere: "If you are upset about this,
 you shouldn't be.")

The semicolon would be another nice right delimiter, 
reminding of closing commands in other areas of computation. 

Below I am varying my former \MakeSet to get a setup 
for assignment commands with space or semicolon as right delimiter. 
The tests use the exclamation mark to show effects of blank spaces 
after the assignment command. You see that there is no problem 
in this respect with space as right delimiter, but it is with semicolon 
(of course). 

space delimits:\par
 \def\MakeCurrentSpace#1{%
 \expandafter\edef\csname#1\endcsname=##1##2 {%
 \def\expandafter\noexpand\csname current#1\endcsname{##1##2}}}
 \MakeCurrentSpace{direction}
 \show\direction
 !\direction= RTL Direction!\currentdirection!\par
 !\direction= LTR Direction!\currentdirection!\par
 !\direction = RTL  Direction!\currentdirection!\par
 !\direction = LTR  Direction!\currentdirection!\par
 !\direction = RTL   Direction!\currentdirection!\par
 !\direction = LTR   Direction!\currentdirection!\par
 \smallskip
 semicolon delimits:\par
 \def\MakeCurrentSemicolon#1{%
 \expandafter\edef\csname#1\endcsname=##1##2;{%
 \def\expandafter\noexpand\csname current#1\endcsname{##1##2}}}
 \MakeCurrentSemicolon{direction}
 \show\direction
 !\direction = RTL;Direction!\currentdirection!\par
 !\direction = LTR;Direction!\currentdirection!\par
 !\direction = RTL; Direction!\currentdirection!\par
 !\direction = LTR; Direction!\currentdirection!\par
 !\direction = RTL;  Direction!\currentdirection!\par
 !\direction = LTR;  Direction!\currentdirection!\par
 \smallskip
 space before semicolon:\par
 !\direction = RTL ;Direction!\currentdirection!\par
 !\direction = LTR ;Direction!\currentdirection!\par
 \def\MakeCurrentSemicolon#1{%
 \expandafter\edef\csname#1\endcsname=##1##2##3;{%
 \def\expandafter\noexpand\csname current#1\endcsname{%
 ##1##2##3}}}
 \MakeCurrentSemicolon{direction}
 \show\direction
 !\direction = RTL ;Direction!\currentdirection!\par
 !\direction = LTR ;Direction!\currentdirection!\par

Cheers, 

    Uwe.