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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