# Using indentation to automatically begin and end itemize environments

This is a question one might answer with "Why the hell would you want to do it?!", sort of an experiment.

What I am looking for is a way to write lists with many levels of nestings (notes for school) in a "natural" way. Previously, I used an elaborate system of Pandoc, LaTeX and Makefiles to generate notes with occasional LaTeX snippets, however, I would like a more integrated workflow (for example, embedding pseudocode in a codebox environment in a Pandoc/Markdown file is quite challenging, as Markdown was designed with HTML in mind).

If I make + an active character, like

\makeatletter
\mathchardef\@my@mathplus=\mathcode+
\catcode+=\active
\def{+}{\ifmmode\@my@mathplus\else\item\fi}
\mateatother


I can write itemizes like

\begin{itemize}
+ one
+ two
+ three
\end{itemize}


however, I would like to get rid of \begin{itemize} and \end{itemize} and write notes like

+ one
+ subitem one
+ subitem two
+ two
+ three


resulting in the nested list, neatly rendered.

Is there a way to achieve this, or I should consider some kind of pre-procession instead? (Creative and mildly insane answers are appreciated.)

-
+1 for the 'insanity' of the question! :) – Count Zero Oct 20 '11 at 18:40
Two comments. (1) It's \def+, not \def{+}. (2) It should better be \DeclareRobustCommand+{\ifmmode\@my@mathplus\else\expandafter\item\fi}; apart from robustness, you can write +[label] as you would with \item[label]. Such shortcuts, however, make the document hard to read and unstructured. – egreg Oct 20 '11 at 20:21
@egreg I didn't really aim for robustness, just a dirty proof of concept. Although thanks for pointing out the mistake with my code (I didn't copy and paste from my text editor but typed it again by hand... my bad). – Kristóf Marussy Oct 21 '11 at 15:45
ConTeXt can process markdown input directly. – Martin Schröder Oct 27 '11 at 17:07
@JuanA.Navarro: Start here. – Martin Schröder Oct 28 '11 at 16:56

Insane answer to an insane question ;)

\documentclass{article}

\def\+{+}

\makeatletter
\catcode\ =12\let\@nl@space= \catcode\ =10
\newcount\@nl@rlevel
\newcount\@nl@llevel
\@nl@llevel=-1

\def\@nl{%
\catcode\ =12
\global\@nl@rlevel=0
\futurelet\@nl@store\@nl@%
}
\def\@nl@gobble#1{\futurelet\@nl@store\@nl@}
\def\@nl@enditemize{
\ifnum\the\@nl@rlevel<\the\@nl@llevel%
\end{itemize}%
\egroup%
\expandafter\@nl@enditemize%
\else%
\ifnum\the\@nl@rlevel=\the\@nl@llevel\else%
\errmessage{Error: inconsistent identation}
\fi%
\fi%
}
\def\@nl@{%
\ifx\@nl@store\@nl@space%
\expandafter\@nl@gobble%
\else%
\catcode\ =10
\ifx\@nl@store+%
\ifnum\the\@nl@rlevel>\the\@nl@llevel%
\bgroup%
\@nl@llevel=\the\@nl@rlevel
\begin{itemize}%
\fi%
\@nl@enditemize%
\item \expandafter\expandafter\expandafter\@gobble%
\else%
\ifx\@nl@store\@nl%
\global\@nl@rlevel=-1\relax\@nl@enditemize\par
\else\space\fi%
\fi%
\fi%
}

\catcode\^^M=\active%
\AtBeginDocument{%
\catcode\^^M=\active%
\let^^M=\@nl%
}%
\catcode\^^M=5
\makeatother

\begin{document}
Some sample text.

+ foo
+ bar
+ a
+ b
+ c. A very long line
split into multiple lines.
+ hehe

Just like nothing happened. Ha!

\+ escaped starting plus

$\lim_{x\to\infty}\frac1x = 0$
\end{document}

-
Surprisingly this really works, and it is yet to explode right into my face, therefore, it is stable enough for my needs. :) – Kristóf Marussy Oct 21 '11 at 16:01
Okay, it seems to play awfully with Babel (at least with the Hungarian one). Replacing the \AtBeginDocument part with a new environment helps, although. – Kristóf Marussy Oct 21 '11 at 16:43
You really seem to like @. – Martin Schröder Oct 27 '11 at 17:05

You may need to redefine ^^M to get this feature. That will be somewhat complicated.

As a suggestion, you may use ++ for a subitem, and +++ for a subsubitem. That's much easier:

\documentclass{article}

\makeatletter
\catcode\+\active
\def\itemX{\@ifnextchar+{\subitemX}{\item}}
\def\subitemX#1{\@ifnextchar+{\subsubitemX}{\subitem}}
\def\subsubitemX#1{\subsubitem}
\def+{\ifmmode\string+\else\expandafter\itemX\fi}
\@makeother\+
\makeatother

\newenvironment{easylist}{\trivlist\item
\def\item{\par\noindent\textbullet\enspace}%
\catcode\+\active
}{\endtrivlist}

\begin{document}

\begin{easylist}
+ foo $a+b$
+ foo
++ bar
++ bar
+++ baz
+++ baz
+ foo
\end{easylist}

\end{document}


See also: nicetext package; pandoc tool.

-
 Note: After reassigning the category codes of ^^M and space char, there is no essential difficulty to distinguish different level of items through indent. However, it is a bit dangerous to redefine newlines and spaces for normal text. – Leo Liu Oct 20 '11 at 18:43 Oh, finally I realize that there is a package easylist, which implement what I said. I just reinvent the wheel. – Leo Liu Oct 21 '11 at 10:29 +1 for "packaged" solution, always preferred. ;-) – DevSolar Oct 21 '11 at 16:05

This is a bit different rather use two commands, one to narrow the paragraph and another to widen it. I have used \i, \w. The first one to make the paragraph narrower (i.e indent but lose the dotless i and the second the \w for wider.

\documentclass{article}
\usepackage{lipsum}
\parskip12pt

\def\w{\wider}
\def\i{\narrower}

\begin{document}
\lipsum[1]
\i \lipsum[2]
\i \lipsum[2]
\i \lipsum[3]
\w \lipsum[4]
\w \lipsum[5]
\w \lipsum[6]
\end{document}


Advantages, never type more than is necessary! Style to suit!

-
 The command \i is already defined. \expandafter\detokenize\expandafter{\i}` – Marco Daniel Oct 20 '11 at 19:10 @MarcoDaniel ... I know that is why I mentioned you lose the dotless i, you don't need a dotless i do you? – Yiannis Lazarides Oct 20 '11 at 19:14 I didn't read this ;-(. Sorry. Nobody need this ;-) but I thought it is important to mention this. – Marco Daniel Oct 20 '11 at 19:15 @MarcoDaniel No problem, you only need it if you type turkish texts, I picked it for its mnemonics i.e, indent, then the indentation level stays until you change it. – Yiannis Lazarides Oct 20 '11 at 19:24