Re: expansion and \processaction

[Wolfgang Schuster <schuster.wolfgang@googlemail.com>]

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}

\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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