Hi Wolfgang!

···<date: 2012-06-07, Thursday>···<from: Wolfgang Schuster>···

> 
> Am 07.06.2012 um 14:05 schrieb Philipp Gesang:
> 
> > Hi all,
> > 
> > my goal is a macro \definestates[foo][...,...] which takes a comma
> > list and creates a monadic macro \foo[n]. \foo[n] should return
> > either the nth item or, if (n > list length), a default. I
> > thought the right tools were \processcommalist to generate the
> > mapping n-><list item>, as well as \processaction to retrieve the
> > items. But naively I didn’t consider expansion ...
> > 
> > My code so far:
> > 
> > ··8<····································································
> > \unprotect
> > 
> > \def\definestates{\dodoubleempty\do_define_states}
> > 
> > \def\do_define_states[#1][#2]{%
> >  \expandafter\edef\csname#1_states\endcsname{%
> >    \nstates0
> >    %% this is supposed to be expanded so we employ the \raw... variety
> >    \rawprocesscommalist[#2]\add_one_state%
> >    unknown=>\dummystate,%
> >    default=>\dummystate,%
> >  }%
> >  \do_do_define_states{#1}%
> > }
> > 
> > \let\dummystate\empty
> > 
> > \newcount\nstates
> > \unexpanded\def\add_one_state#1{%
> >  \advance\nstates\plusone
> >  \the\nstates=>#1,%
> > }
> > 
> > \def\do_do_define_states#1{%
> >  \expandafter\def\csname#1\endcsname
> >    {\expandafter\dosingleempty\csname do_#1\endcsname}%
> >  \expandafter\def\csname do_#1\endcsname[##1]{%
> >    \iffirstargument
> >      % <[DBG] cmd:#1, state:##1>\par
> >      \edef\currentstates{\csname#1_states\endcsname}%
> >      %% At this point \currentstates should yield the whole mapping so
> >      %% we can use it with \processaction. But ...
> >      % \show\currentstates
> >      % \currentstates\par
> >      %% ... here it still contains
> >      %%    \nstates 0 \rawprocesscommalist [foo,bar,baz] ...
> >      %% and the next directive has an empty result:
> >      \rawprocessaction[##1][\currentstates]%
> >    \fi
> >  }%
> > }
> > 
> > \protect
> > \starttext
> > 
> > \definestates[mystates][foo,bar,baz]
> > %% At this point I’d like \mystates_states to contain (literally)
> > %%   “1=>foo,2=>bar,3=>baz,unknown=>,default=>,”
> > %% so the following command
> > \mystates[1]  % -> foo
> > %% would be equivalent to
> > %%    \processaction[1][1=>foo,2=>bar,3=>baz,unknown=>,default=>,]
> > \mystates[2]  % -> bar
> > \mystates[42] % -> dummy
> > 
> > \stoptext
> > ··8<····································································
> > 
> > My question: How can I use \[raw]processcommalist in an expanded
> > definition? How can I get \[raw]processcommalist to operate on
> > the expansion of its second argument? Does this even make sense?
> > If not, what is the proper way?
> 
> \unprotect
> 
> \unexpanded\def\definestates
>   {\dodoubleargument\definestates_indeed}
> 
> \def\definestates_indeed[#1][#2]%
>   {\setuevalue{#1}{\states_entry[#2]}}
> 
> \unexpanded\def\states_entry
>   {\dodoubleargument\states_entry_indeed}
> 
> \def\states_entry_indeed[#1][#2]%
>   {\getcommalistsize[#1]%
>    \ifnum#2>\commalistsize
>      {\tttf NO ENTRY!}%
>    \else
>      \getfromcommalist[#1][#2]\commalistelement
>    \fi}

Thanks very much. This solves my problem. Very convenient that I
can rewrite it to use commacommand.

Philipp

> 
> \protect
> 
> \starttext
> 
> \definestates[mystates][foo,bar,baz]
> 
> \starttabulate
> \NC  2 \EQ \mystates [2] \NC\NR
> \NC 42 \EQ \mystates[42] \NC\NR
> \stoptabulate
> 
> \stoptext
> 
> Wolfgang
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