Macros that define other macros, which also define other macros

Question

I would like to define a TeX 'macro-building' command (let us call it \buildmacro) that takes as argument a string of 'normal' characters (e.g., Title) and which satisfies the followings:

• the command \buildmacro{Title} defines the counter with the name TitleXcounter and initializes it to 0.

• when issuing at some point in the file the TeX command \Title{<arg>}, this will have the effect of increasing the counter TitleXcounter and then putting the value <arg> into a new TeX macro with the name \Title-<x>, where <x> is the current value value of TitleXcounter;

  here, <arg> is a piece of TeX code (that can contain text, maths, paragraphs of any other TeX commands).

Consider the following minimal example:

\documentclass{article}
\usepackage{ifthen}


\def\buildmacro#1{...}% the definition of \buildmacro

\begin{document}

\buildmacro{Title}

% 'Read' several titles

\Title{The first title}
\Title{The second title}
\Title{The third title}

\newcount\tempcount
\tempcount=1\relax

% 'List' all the Titles
\whiledo{\the\tempcount<\numexpr \thetitleXcounter+1\relax}
        {%
         \textsc{\csname title-\the\tempcount\endcsname}\par
         \advance\tempcount by 1\relax
        }

\end{document}

I 'played' with \csname and \endcsname, \expandafter, \def, \gdef and the \long versions, but with no 'luck'.

Edited (in order to answer some of the comments):

The purpose of this is to have a simple mechanism to create a set of indexed commands with the same root-name (similar to a list of commands). One can always use the \csname <...> \endcsname construct to issue the commnds.

Answer 1

From the description of the flow required this seems quite simple

\newcommand\buildmacro[1]{%
  % Create a new counter named after the argument
  \newcounter{#1Xcounter}%
  % Create a new command named after the argument,
  % itself taking one argument
  \expandafter\newcommand\csname #1\endcsname[1]{%
    % Step the counter
    \stepcounter(#1Xcounter)%
    % Store the argument
    \expandafter\newcommand\csname #1-\arabic{#1Xcounter}\endcsname
      {##1}%
  }%
}

As a plain version was also requested

\long\def\buildmacro#1{%
  \csname newcount\expandafter\endcsname\csname #1Xcounter\endcsname
  \long\expandafter\def\csname #1\endcsname##1{%
    \global\expandafter\advance\csname #1Xcounter\endcsname by 1
    \expandafter\def\csname #1-\expandafter\number\csname #1Xcounter\endcsname
      \endcsname
      {##1}%
  }%
}

Answer 2

As I mentioned in a comment, neither a hyphen nor a numeral can be used when constructing macro names unless you will always write the equivalent of \csname ... \endcsname or ensure the catcodes are changed when using them.

Hence, it is necessary to modify the user interface from that suggested.

The basic idea seems to be to create a series of indexed lists of argument which can be retrieved by giving the name of the list and the index of the item within that list.

This could be implemented using comma-separated lists. Here is a suggested interface which uses only expl3 syntax considered stable by the developers:

\buildmacro{<list identifier>}
\addmacro{<list identifier>}{<item to be added>}
\fetchmacro{<list identifier>}{<index of item to be fetched>}
\listmacro{<list identifier>}

The first sets things up by initialising a new list. The second adds an item to a list. The third fetches an item from a list. The fourth lists all items in a list sequentially.

Proof of concept (though hardly an original one):

\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\cs_new_protected_nopar:Nn \digitalink_buildmacro:n
{
  \clist_new:c { g_digitalink_#1_clist }
}
\NewDocumentCommand \buildmacro { m }
{
  \digitalink_buildmacro:n { #1 }
}
\NewDocumentCommand \addmacro { m +m }
{
  \clist_gput_right:cn { g_digitalink_#1_clist }
  {
    #2
  }
}
\NewDocumentCommand \fetchmacro { m m }
{
  \clist_item:cn { g_digitalink_#1_clist } { #2 }
}
\NewDocumentCommand \listmacro { m }
{
  \clist_use:cn { g_digitalink_#1_clist } { \par }
}
\ExplSyntaxOff
\begin{document}
\buildmacro{dititle}
\addmacro{dititle}{Here's some text.}
\addmacro{dititle}{Here's some more.}
\fetchmacro{dititle}{1}
\fetchmacro{dititle}{2}
\fetchmacro{dititle}{1}

List:

\listmacro{dititle}
\end{document}

Answer 3

A \@namedef and \@nameuse version, faking 'macro' names that would not be possible without catcode change.

The allocation of \newcounter inside of macros may cause troubles with counter registers.

\documentclass{article}

\makeatletter
\newcommand{\buildmacro}[1]{%
  \newcounter{#1Xcounter}%
    \expandafter\newcommand\csname #1\endcsname[1]{%
      \stepcounter{#1Xcounter}%
      \@namedef{#1-\number\value{#1Xcounter}}{##1}%
  }
}

\newcommand{\displaymacrocontent}[2]{%
  \@nameuse{#1-#2}%
}
\makeatother



\begin{document}

\buildmacro{Title}
\Title{The first title}
\Title{The second title}
\Title{The third title}

\newcount\tmpcntr

\loop\unless\ifnum\tmpcntr > 4
\advance\tmpcntr by 1
\displaymacrocontent{Title}{\number\tmpcntr}

\repeat



\end{document}

Answer 4

The effect you're showing in your pseudocode is much more easily obtained with a list macro, that allows to do a loop without having to know how many objects are in it and without stepping counters.

\documentclass{article}

\makeatletter
\newcommand{\Titlecontainer}{\@empty}% initialize
\newcommand{\Title}[1]{%
  \expandafter\def\expandafter\Titlecontainer\expandafter{%
    \Titlecontainer\LISTSEP{#1}%
  }%
}
\makeatother

\begin{document}

\Title{The first title}
\Title{The second title}
\Title{The third title}

% 'List' all the Titles
\begingroup % keep the change to \LISTSEP local
\def\LISTSEP#1{\textsc{#1}\par}
\Titlecontainer
\endgroup

\end{document}

An “abstract” version:

\documentclass{article}

\makeatletter
\newcommand{\Titlecontainer}{\@empty}% initialize
\newcommand{\Title}[1]{%
  \expandafter\def\expandafter\Titlecontainer\expandafter{%
    \Titlecontainer\LISTSEP{#1}%
  }%
}
\newcommand{\listmap}[2]{% #1 is the list name, #2 the code
  \begingroup\def\LISTSEP##1{#2}#1\endgroup
}
\makeatother

\begin{document}

\Title{The first title}
\Title{The second title}
\Title{The third title}

% 'List' all the Titles
\listmap{\Titlecontainer}{\textsc{#1}\par}

\end{document}

Even easier with expl3:

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\NewDocumentCommand{\Title}{m}
 {
  \seq_put_right:Nn \digitalink_titles_seq { #1 }
 }
\NewDocumentCommand{\ProcessTitles}{+m}
 {
  \seq_map_inline:Nn \digitalink_titles_seq { #1 }
 }
\seq_new:N \digitalink_titles_seq
\ExplSyntaxOff

\begin{document}

\Title{The first title}
\Title{The second title}
\Title{The third title}

\ProcessTitles{\textsc{#1}\par}

\newcounter{titlecount}
\ProcessTitles{\stepcounter{titlecount}\arabic{titlecount} -- #1\par}

\end{document}

---

Abstract versions

Classic method

\documentclass{article}

\makeatletter
\newcommand{\definelist}[1]{%
  \@namedef{#1}##1{%
    \expandafter\def\csname #1@container\expandafter\expandafter\expandafter\endcsname
    \expandafter\expandafter\expandafter{%
      \csname #1@container\endcsname\LISTSEP{##1}%
    }%
  }%
  \@namedef{#1@container}{\@empty}% initialize
}
\newcommand{\maplist}[2]{%
  \begingroup
  \def\LISTSEP##1{#2}%
  \@nameuse{#1@container}%
  \endgroup
}
\makeatother

\definelist{Title}

\begin{document}

\Title{The first title}
\Title{The second title}
\Title{The third title}

% 'List' all the Titles
\maplist{Title}{\textsc{#1}\par}

\newcounter{tempcount}
\maplist{Title}{\stepcounter{tempcount}\arabic{tempcount} -- #1\par}

\end{document}

With expl3

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\NewDocumentCommand{\definelist}{m}
 {
  \seq_new:c { l_digitalink_list_#1_seq }
  \cs_new_protected:cpn { #1 } ##1
   {
    \seq_put_right:cn { l_digitalink_list_#1_seq } { ##1 }
   }
 }
\NewDocumentCommand{\maplist}{m +m}
 {
  \seq_map_inline:cn { l_digitalink_list_#1_seq } { #2 }
 }
\ExplSyntaxOff

\definelist{Title}

\begin{document}

\Title{The first title}
\Title{The second title}
\Title{The third title}

% 'List' all the Titles
\maplist{Title}{\textsc{#1}\par}

\newcounter{tempcount}
\maplist{Title}{\stepcounter{tempcount}\arabic{tempcount} -- #1\par}

\end{document}