# Processing Lists

See Comma Separated Lists for details of lists in ConTeXt

## Processing a comma-separated list of values

Suppose you defined a command like this one somewhere in your document:

\def\IHaveTo#1#2{I have to #1 on #2.\par}


So calling

\IHaveTo{tidy up}{Monday}


This will print out:

But sometimes you have to repeat some task more than once. In this case you can define a new command:

\def\MyMumOrderedMeTo[#1]#2%
{\processcommalist[#1]{\IHaveTo{#2}}}


Calling

\MyMumOrderedMeTo[Monday,Wednesday,Saturday]{tidy up}


will spare you some typing (but not some tidying up!):

In case a command \IHaveTo is already defined in a slightly different way:

\def\IHaveTo[#1]#2{I have to #2 on #1.\par}


you can define \MyMumOrderedMeTo as:

\def\MyMumOrderedMeTo[#1]#2%
{\begingroup
\def\processitem##1{\IHaveTo[##1]{#2}}%
\processcommalist[#1]\processitem
\endgroup}


This, again, produces:

## Processing a dash-separated list of values

Sometimes you have more work to do than just that boring stuff at home. And as it is quite important as well, you don't want to loose your time enumerating all of the tasks. Being able to do something like

\IHaveToDoTheTasks[1-4,7,9-11]{until tomorrow}


may sound like a good idea.

\def\IHaveToDoTheTask[#1]#2{The task #1 has to be done #2.\par}


You have to define some macros first (thanks to Taco!):

% a few auxiliary core macros are needed to uncompress the list.
%
% \uncompresslist is the twin of the already existing \compresslist
% which works in the other direction (syst-new)
%
\unprotect

% I guess this function is already available but couldnt find it...
%
\def\apptomac#1#2%
{\ifx#1\empty\def#1{#2}\else \@EA\def\@EA#1\@EA{#1,#2}\fi}

% the next macro does this:
%
% \itemwithdash<<9-11>>- => \dorecurse {<<1+11-9>>}
%     {\apptomac\uncompressedlist<<9-1+\recurselevel>>}
%
% (the 1+ and -1 are needed to solve a counter offset.)
\def\itemwithdash#1-#2-%
{\@EA\dorecurse\@EA
{\the\numexpr 1+#2-#1\relax}%
{\@EA\apptomac\@EA\uncompressedlist\@EA
{\the\numexpr #1-1+\recurselevel\relax}}}%

% top level. The result will be in \uncompressedlist
\def\uncompresslist[#1]%
{\def\uncompressedlist{}%
\def\processitem##1%
{\doifinstringelse{-}{##1}
{\itemwithdash##1-}
{\apptomac\uncompressedlist{##1}}}%
\processcommalist[#1]\processitem }

\protect


And then you're ready to define

\def\IHaveToDoTheTasks[#1]#2%
{\begingroup
\uncompresslist[#1]% <= Yeah!
\processcommacommand[\uncompressedlist]\processitem
\endgroup}


So - what are you still waiting for? Go back to work and do them right away!

The code for processing dash-separated lists resulted from thread [1] and will be used in some modules such as RawSteps. It would be nice if processing dash-separated lists of values would make it into the ConTeXt core.

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