Re: expansion and \processaction

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

Am 07.06.2012 um 17:34 schrieb Philipp Gesang:

> 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 comma command.

You can also try to use a Lua variant.

\def\states_entry_indeed[#1][#2]%
 {\startlua
  local entries = utilities.parsers.settings_to_array("#1")
  local entry   = entries[#2]
  if entry then
    context(entry)
  else
    context("\\tttf NO ENTRY!")
  end
  \stoplua}

Wolfgang
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