Re: Checking for a Unicode prefix of a Unicode string

[Hans Hagen via ntg-context <ntg-context@ntg.nl>]

On 11/27/2021 6:13 PM, Joey McCollum wrote:
> All right, I think I've solved the expansion problem I described before: 
> to ensure that the first input is expanded when it is passed to Lua, I 
> have to pass it as [==[#1]==], not "#1". But the updated MWE below still 
> does not seem to work, as the \DoIfPrefixElse macro is printing "NOP" 
> instead of "YES":
> 
> ```
> 
> \starttexdefinition loc [#1]
> 
> \doifassignmentelse{#1} {
> 
> % if an assignment, then parse and format accordingly
> 
> \getparameters[loc][#1]
> 
> % Was a section number specified?
> 
> \doifdefined{locsec} {
> 
> § \locsec
> 
> }
> 
> } {
> 
> % otherwise, just print the input as-is
> 
> #1
> 
> }
> 
> \stoptexdefinition
> 
> 
> \def\DoIfPrefixElse#1#2{\ctxlua{commands.doifelse(string.find([==[#2]==],"^"..[==[#1]==]))}}
> 
> 
> \def\currentbtxloctext{\loc[sec=31]}
> 
> 
> \starttext
> 
> \currentbtxloctext\blank
> 
> \DoIfPrefixElse{§}{\currentbtxloctext}{YES}{NOP}
> 
> \stoptext
> 
> ```
> 
> Indeed, if I add a simple \doifelse equality check, it looks like the 
> value I expect is not the same as what the macro produces, even though 
> they look identical:
> 
> ```
> 
> \starttexdefinition loc [#1]
>      \doifassignmentelse{#1} {
>          % if an assignment, then parse and format accordingly
>          \getparameters[loc][#1]
>          % Was a section number specified?
>          \doifdefined{locsec} {
>              § \locsec
>          }
>      } {
>          % otherwise, just print the input as-is
>          #1
>      }
> \stoptexdefinition
> 
> \def\DoIfPrefixElse#1#2{\ctxlua{commands.doifelse(string.find([==[#2]==],"^"..[==[#1]==]))}}
> 
> \def\currentbtxloctext{\loc[sec=31]}
> 
> \starttext
>      § 31\blank%the raw text we expect
>      \currentbtxloctext\blank%the text as produced by the macro
>      \doifelse{\currentbtxloctext}{§ 31}{YES}{NOP}\blank% should output 
> YES, but doesn't
>      \DoIfPrefixElse{§}{\currentbtxloctext}{YES}{NOP}\blank% should 
> output YES, but doesn't
> \stoptext
> 
> ```
> 
> What am I missing here?
Expansion hell ... and i fear that you draw yourself into more and more 
trouble with this approach (which is why you don't find that kind of 
hackery in the core unless we're real desperate) so maybe try to explain 
what the real problem is that needs to be solved. Parsing tex is seldom 
a solution (at least not in context).

You can add:

     \edef\Whatever{\currentbtxloctext}\meaning\Whatever
     \doifelse{\currentbtxloctext}{§ 31}{YES}{NOP}\blank

and see what comes back. Now, as always in tex, there's of course a 
solution because after all it's a programming language too (and at some 
point these solutions start looking so complex that one enters guru state)

\starttexdefinition loc [#1]
     \beginlocalcontrol
     \doifassignmentelse{#1} {
         \getparameters[loc][#1]
         \doifdefinedelse{locsec} {
         \endlocalcontrol
             § \locsec
         } {
             \endlocalcontrol
         }
     } {
         \endlocalcontrol
         #1
     }
\stoptexdefinition

a curious mix between a fully expanded result, using protected macros 
and hiding what tex does but hard to explain

Hans

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                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
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