Environment for typesetting UML use cases

usecase.sty

%
% A simple description-like environment that can be used for writing UML use
% cases.
%

\NeedsTeXFormat{LaTeX2e}[1994/06/01]
\ProvidesPackage{usecase}[2011/03/21 v0.1 A usecase environment.]

%
% Required so we can use inline arithmetic in the usecase environment
% defition. Could be removed and the code below could use \addtolength
% instead.
%
\RequirePackage{calc}

%
% Used in the usecase environment to ensure that the \usecaselabelwidth has
% been set.
%
\RequirePackage{ifthen}

%
% The style of the labels
%
\newcommand{\usecaselabelstyle}{%
  \normalfont\bfseries
}

%
% Used below to set the label width to the width of the longest label
%
\newlength{\usecaselabelwidth}
\setlength{\usecaselabelwidth}{0pt}
\newcommand{\maxusecaselabel}[1]{%
  \settowidth{\usecaselabelwidth}{\usecaselabelstyle #1}%
}

%
% The definition of the usecase environment -- where all the 'magic' happens
%
\newenvironment{usecase}{%
  \begin{list}{}{%
    \ifthenelse{\lengthtest{\usecaselabelwidth=0pt}}{%
      \PackageError{usecase}{You must call \string\maxusecaselabel}{%
        You should call \string\maxusecaselabel{LongestUseCaseLabel}, where
        \MessageBreak
        LongestUseCaseLabel is the longest label used in your usecase
        environment.
      }%
    }{}%
    \renewcommand{\makelabel}[1]{%
      \usecaselabelstyle ##1%
      \hfil
    }%
    \setlength{\labelwidth}{\usecaselabelwidth}%
    \setlength{\leftmargin}{\labelwidth+\labelsep}%
  }%
}{%
  \end{list}%
}

\endinput