% \iffalse meta-comment
%
% This is sharedline.dtx, a documented TeX source file.
%
% To get the user documentation, run this file through LaTeX:
% > pdflatex sharedline.dtx
% > makeindex -s gind.ist sharedline.idx
% > pdflatex sharedline.dtx
%
% To extract the package file sharedline.sty:
% > tex sharedline.ins
%
% Copyright 2025 by Jacob Smullyan
%
% This work may be distributed and/or modified under the
% conditions of the LaTeX Project Public License, either version 1.3c
% of this license or (at your option) any later version.
% The latest version of this license is in
%   http://www.latex-project.org/lppl.txt
% and version 1.3 or later is part of all distributions of LaTeX
% version 2005/12/01 or later.
%
% \fi
%
% \iffalse
%<*driver>
\ProvidesFile{sharedline.dtx}
  [2025/06/26 v1.0 A package for typesetting shared lines in verse]
\documentclass{ltxdoc}
\usepackage{parskip}
\usepackage[T1]{fontenc}
\usepackage{verse}
\GetFileInfo{sharedline.dtx}
\EnableCrossrefs
\CodelineIndex
\RecordChanges
\title{The \textsf{sharedline} package\thanks{This package is licensed under the LPPL v1.3c or later.}}
\author{Jacob Smullyan}
\date{\fileversion, \filedate}
\begin{document}
  \DocInput{sharedline.dtx}
\end{document}
%</driver>
% \fi
%
% \changes{v1.0}{2025/06/26}{Initial release}
%
% \maketitle
% \begin{abstract}
% The \textsf{sharedline} package provides a robust and flexible solution for
% typesetting shared lines in dramatic verse, such as in the plays of
% Shakespeare. It allows a single line of verse to be split across multiple
% speakers while maintaining perfect horizontal alignment, creating the
% visual effect of a single, continuous line of iambic pentameter.
% \end{abstract}
%
% \tableofcontents
%
% \section{Introduction}
% Typesetting dramatic verse presents a unique challenge: a single metrical
% line is often shared between two or more characters. Standard use of the
% \texttt{verse} environment breaks the visual continuity of the line. This
% package introduces two simple commands, \cs{shareline} and \cs{linefeed},
% that work together to solve this problem elegantly.
%
% The ``starter'' command, \cs{shareline}, typesets the first part of a
% shared line and saves its width. The ``continuation'' command,
% \cs{linefeed}, is then used for all subsequent parts. It typesets an
% optional introductory text (such as a speaker prompt) at the left margin,
% then indents the verse text so that it begins at the horizontal position
% where the previous segment ended. It then adds its own verse width to the
% running total, so a line can be split any number of times.
%
% The package works naturally within the \texttt{verse} environment but does
% not depend on it. The user retains full control over line breaks, using
% \texttt{\textbackslash\textbackslash}, \texttt{\textbackslash\textbackslash!},
% or other standard mechanisms.
%
% \section{Installation}
% To install the package, place the \texttt{sharedline.sty} file in a
% location where your \TeX\ distribution can find it. For a local
% installation, this is typically in your \texttt{texmf} tree (e.g.,
% \texttt{TEXMFHOME/tex/latex/sharedline/}). After moving the file, you may
% need to refresh your distribution's file database.
%
% If you are using this \texttt{.dtx} file, you can extract the package by
% running the command: \texttt{tex sharedline.ins}
%
% \section{Usage}
% The package provides two commands. They work naturally within the
% \texttt{verse} environment but do not depend on it.
%
% \DescribeMacro{\shareline}
% \cs{shareline}\marg{full text} \\
% Starts a shared line. The mandatory argument contains the entire first
% segment, including any speaker prompt. The command typesets its argument
% and saves its total horizontal width as the baseline for subsequent
% indentation. It does not add a line break; you must add one manually
% (e.g., with \texttt{\textbackslash\textbackslash}).
%
% \DescribeMacro{\linefeed}
% \cs{linefeed}\oarg{intro}\marg{verse} \\
% Continues a shared line. Used for all subsequent parts (second, third, etc.).
% \begin{itemize}
%   \item \oarg{intro}: Optional introductory text (e.g., a speaker prompt),
%   typeset at the left margin.
%   \item \marg{verse}: The verse text for this segment, indented so that it
%   begins at the horizontal position where the previous segment ended.
% \end{itemize}
% After typesetting, the width of the verse text (not the intro) is added to
% the running total, so that subsequent \cs{linefeed} calls indent further.
% Like \cs{shareline}, this command does not add a line break.
%
% \subsection{Example: A Two-Way Split}
% \begin{verbatim}
% \begin{verse}
%   \shareline{ANNE: I would I knew thy heart.}\\
%   \linefeed[GLOUCESTER: ]{'Tis figured in my tongue.}\\
% \end{verse}
% \end{verbatim}
%
% \subsection{Example: A Three-Way Split}
% Notice that \cs{linefeed} is used for both the second and third parts. A
% manual line break is required after each segment except the last.
% \begin{verbatim}
% \begin{verse}
%   \shareline{GUARD 1: Who goes there?}\\
%   \linefeed[GUARD 2: ]{Speak now, or I swear}\\
%   \linefeed[GUARD 1: ]{I'll shoot!}\\
% \end{verse}
% \end{verbatim}
%
% \subsection{Example: Without Speaker Prompts}
% The syntax remains clean when no prompts are needed. Simply omit the
% optional argument for \cs{linefeed}.
% \begin{verbatim}
% \begin{verse}
%   \shareline{A path of dust and dreams beneath the sun,}\\
%   \linefeed{a journey to a star.}\\
% \end{verse}
% \end{verbatim}
%
% \StopEventually{\PrintChanges\PrintIndex}
%
% \section{Implementation}
% We begin by identifying the package and its dependencies.
%
%    \begin{macrocode}
%<*package>
\ProvidesPackage{sharedline}[2025/06/26 v1.0]

\RequirePackage{xparse}
%    \end{macrocode}
%
% We use a number of internal lengths and saveboxes. To prevent clashes
% with user-defined macros or other packages, we use the \verb|@| symbol
% in their names and wrap the definitions in \cs{makeatletter} and
% \cs{makeatother}. The prefix \texttt{sl@} is used for ``sharedline''.
%
%    \begin{macrocode}
\makeatletter

\newsavebox{\sl@linebox}
\newlength{\sl@linelength}
\newsavebox{\sl@subtractbox}
\newsavebox{\sl@addbox}
%    \end{macrocode}
%
% \begin{macro}{\shareline}
% The starter command. It takes a single mandatory argument
% containing the full text of the first segment, including any speaker prompt.
% It places the argument into a box to measure its width, saves this width
% globally into \cs{sl@linelength}, and typesets the argument.
%    \begin{macrocode}
\NewDocumentCommand{\shareline}{m}{%
  \sbox{\sl@linebox}{#1}%
  \global\settowidth{\sl@linelength}{\usebox{\sl@linebox}}%
  #1%
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\linefeed}
% The continuation command, used for all subsequent parts of a
% shared line. It takes an optional intro and a mandatory verse segment.
% It measures the intro width, typesets the intro, inserts a horizontal space
% equal to the accumulated length minus the intro width, typesets the verse,
% and adds the verse width to the running total.
%    \begin{macrocode}
\NewDocumentCommand{\linefeed}{O{} m}{%
  \sbox{\sl@subtractbox}{#1}%
  #1%
  \hspace*{\dimexpr\sl@linelength - \wd\sl@subtractbox\relax}%
  #2%
  \sbox{\sl@addbox}{#2}%
  \global\addtolength{\sl@linelength}{\wd\sl@addbox}%
}

\makeatother

\endinput
%    \end{macrocode}
% \end{macro}
%
%</package>
% \Finale