Different content on left and right pages

Question

I would like to create a document/book/memoir (haven't chosen a class yet) that has completely different content on all the left-hand side pages and different content on all the right-hand side pages.

Ultimately, what I am trying to achieve is to have the actual text on the left-hand side pages and then commentary about the text on the right-hand side pages.

I can also see a similar use if creating a book with dual languages with each language on their own side of the book.

How can I go about setting this up?

PS. I wasn't sure of a proper tag to use for my question.

Answer 1

The example below uses a custom macro, that I called \xxxx in a display of imagination (I left as exercise find a better name), using afterpage.

Usage:

\xxxx{text in left page}{comment in right page}

The comments are conditionally colored to check easily when the comment are shorter that the original text and thus they should not stretch the commented text (always a good idea).

Note that when there are not enough space for the text and/or the comment you should add \newpage twice.

Example:

\documentclass{article}
\usepackage{geometry}
\usepackage{lipsum,xcolor}
\usepackage{afterpage}
\parindent0pt\parskip 2em   
\newsavebox\mytext
\newsavebox\mycomment
\newcommand\xxxx[2]{
\savebox\mytext{\parbox[t]{\linewidth}{#1}}
\savebox\mycomment{\parbox[t]{\linewidth}{#2}}
\ifdim\dp\mytext>\dp\mycomment
\noindent\begin{minipage}[t][\dp\mytext][t]{\linewidth}#1\end{minipage}
\afterpage{% shorter comment in blue
\savebox\mytext{\parbox[t]{\linewidth}{#1}}
\noindent\begin{minipage}[t][\dp\mytext][t]{\linewidth}
\color{blue!50!black}#2\end{minipage}}
\else
\noindent\begin{minipage}[t][\dp\mycomment][t]{\linewidth}#1\end{minipage}
\afterpage{% longer comment in red
\savebox\mycomment{\parbox[t]{\linewidth}{#2}}
\noindent\begin{minipage}[t][\dp\mycomment][t]{\linewidth}
\color{red!50!black}#2\end{minipage}}
\fi}
\begin{document}
~\newpage % first odd page 
\xxxx{\lipsum[1][1-10]}{Brief comments  in blue}
\xxxx{\lipsum[2][1-4]}{Boring comments in red. \lipsum[3]}
\xxxx{\lipsum[4][1-6]}{Another boring comment \lipsum[5][1-12]}
\xxxx{\lipsum[6]}{There are a hidden cat here.}
\newpage % Blank page for comments
\newpage
\xxxx{\lipsum[7]}{\lipsum[8]}
\xxxx{\lipsum[9]}{\lipsum[10]}
\xxxx{\lipsum[11]}{\lipsum[12]}
\xxxx{\lipsum[13]}{\lipsum[14]}
\xxxx{\lipsum[15]}{\lipsum[16]}
\newpage % Blank page for comments
\newpage
\xxxx{\lipsum[17]}{\lipsum[18]}
\xxxx{\lipsum[19]}{xxxx\lipsum[20]}
\xxxx{\lipsum[21]}{xxxx\lipsum[22]}
\xxxx{\lipsum[23]}{xxxx\lipsum[24]}
\xxxx{\lipsum[25]}{xxxx\lipsum[26]}
\end{document}

But without reinvent the wheel, as commented John Kormylo, paracol is another (better) option:

\documentclass{article}
\usepackage{geometry,parskip}
\usepackage{lipsum}
\usepackage{paracol}
\begin{document}
~ \newpage
\begin{paracol}[1]{2}
\begin{leftcolumn} \lipsum[1][1-2] \end{leftcolumn}
\begin{rightcolumn} \lipsum[2] \end{rightcolumn}
\end{paracol}
\begin{paracol}[1]{2}
\begin{leftcolumn} \lipsum[3] \end{leftcolumn}
\begin{rightcolumn} \lipsum[4] \end{rightcolumn}
\end{paracol}
\begin{paracol}[1]{2}
\begin{leftcolumn} \lipsum[5] \end{leftcolumn}
\begin{rightcolumn} \lipsum[6] \end{rightcolumn}
\end{paracol}
\end{document}