Define new commands which use line-break as delimiter instead of curly braces

Question

I would like to use commands without having curly braces {} as delimiters. Mostly I would like that the commands work with a line-break as the delimiter.

Herewith a simple example, which does not work (My is displayed but missing the line)

\documentclass[12pt]{report}
\def\chap #1 {\chapter{#1}}
\def\sec #1 {\section{#1}}
\def\subsec #1 {\subsection{#1}}
\def\li #1 {\begin{itemize}\item #1\end{itemize}}
\begin{document}
\chap My First Chapter
\sec My First Section
\subsec My First Section
\li lkdsjfaljsfad
\li lkdsjfaljsfad
\li lkdsjfaljsfad
\end{document}

Would you know how to make it work?

Answer 1

Here's a LuaLaTeX-based solution. It sets up a Lua function that operates at a very early stage of processing: it scans all lines of input and simply replaces instances of \chap ..... with \chapter{.....}. (In Lua's string.gsub function, the $ character serves as the end-of-line marker.) Ditto for \sec ..., \subsec ..., and \li .... With this setup, LaTeX only gets to "see" the standard macros with standard argument formation; no need to define macros called \chap, \sec, etc.

% !TeX program = lualatex
\documentclass[12pt]{report}
\usepackage{luacode}
\begin{luacode}
function scan_ahead ( s )
  s = string.gsub ( s , "\\chap%s+(.*)$" , "\\chapter{%1}" )
  s = string.gsub ( s , "\\sec%s+(.*)$" , "\\section{%1}" )
  s = string.gsub ( s , "\\subsec%s+(.*)$" , "\\subsection{%1}" )
  s = string.gsub ( s , "\\li%s+(.*)$" , "\\begin{itemize}\\item %1\\end{itemize}")
  return s
end
luatexbase.add_to_callback ( "process_input_buffer",  scan_ahead , "scan_ahead" )
\end{luacode}

\begin{document}
\chap My First Chapter
\sec My First Section
\li lkdsjfaljsfad
\li abc def ghi
\subsec My First Section
\li jkl mno pqr stu
\end{document}

Answer 2

I don't recommend this -- it does not look well and breaks the tradition of LaTeX commands.

The code is taken from egreg's answer at Using end-of-line delimiter in plain Tex macro (upvoted of course ;-))

There's actually nothing to gain from this and distracts from (proof)reading codes.

Especially \li is not really useful short version \item anyway.

The endline character has usually the catcode 5, so this is converted to a space or \par token (depending on the state) first before further processing the input. In order to make TeX recognize the end of line the catcode has to be changed, to 12 ('other'), in a group, so use

\def\chap{\begingroup\catcode`\^^M=12 \xchap}
{\catcode`\^^M=12 %
 \gdef\xchap#1^^M{\chapter{#1}\endgroup}%
}

to read the content until the end of the line and let the temporary macro \xchap to the display of \chapter{...} etc. (the same for \sec and \subsec.)

Of course, such approaches will break \chap[foo]{foo bar}, i.e. the short version of the chapter title meant for ToC and page headings are not available any longer.

\documentclass[12pt]{report}


\def\chap{\begingroup\catcode`\^^M=12 \xchap}
{\catcode`\^^M=12 %
 \gdef\xchap#1^^M{\chapter{#1}\endgroup}%
}


\def\sec{\begingroup\catcode`\^^M=12 \xsec}
{\catcode`\^^M=12 %
 \gdef\xsec#1^^M{\section{#1}\endgroup}%
}

\def\subsec{\begingroup\catcode`\^^M=12 \xsubsec}
{\catcode`\^^M=12 %
 \gdef\xsubsec#1^^M{\subsection{#1}\endgroup}%
}



\begin{document}
\chap My First Chapter
\sec My First Section
\subsec My First Section
\begin{itemize}
\item lkdsjfaljsfad
\item lkdsjfaljsfad
\item lkdsjfaljsfad
\end{itemize}
\end{document}

However, this is code golfing, in my point of view.