Compress a list of page references

This has not turned out as pretty as I initially hoped, but it seems to work. It takes a list of integers and it compacts them as you described. The code should be pretty self-explanatory, I can't help but feel it should be possible to do it much shorter, but hey.

\documentclass{article}
\makeatletter
\let\dotlessi\i
\newcount\last
\def\range#1{%
  \last 0\relax
  \def\temp{}
  \def\first{}
  \@for\i:=#1\do{%
    \ifnum\the\last=0%start
      \edef\temp{\i}%
    \else%
      \advance\last 1\relax%
      \ifnum\last=\i%
        \ifx\first\empty%
          \let\@temp\temp%
          \edef\temp{\@temp--}%
          \def\first{x}%
        \else%
        \fi%
      \else%
        \ifx\first\empty%
          \let\@temp\temp%
          \let\j\i%
          \edef\temp{\@temp,\j}
        \else%
          \advance\last -1\relax%
          \let\@temp\temp%
          \let\j\i%
          \edef\temp{\@temp\the\last,\j}%
        \fi%
      \fi%
    \fi%
    \last \i\relax%
  }%
  [\temp]%
}
\makeatother
\let\i\dotlessi
\begin{document}
\noindent
Some test ranges\\
\range{1,2,3,4,7}\\
\range{1,3,5,7}\\
\range{1,3,4,5,7}\\
\range{}
\end{document}

And the output:

PS: what happened to the tex.sx image uploading? :(

The latest version (V0.18) of cleveref includes \cpageref and \cpagerefrange which can be used to refer to page ranges as well. It is not yet on CTAN, so for the test below I obtained it from Toby Cubitt's site:

\documentclass{book}
\usepackage{lipsum}
\usepackage{cleveref}% load last

\begin{document}

\chapter{One}
\section{One-One}\label{One-One}
\lipsum[1-4]\label{One-Two}

\chapter{Two}
\section{Two-One}\label{Two-One}
\section{Two-Two}\label{Two-Two}
\section{Two-Three}\label{Two-Three}

\chapter{Three}
\section{Three-One}\label{Three-One}
\lipsum[1-9]

\newpage
Section One-One is on Page~\pageref{One-One}\par
Section One-Two is on Page~\pageref{One-Two}\par
Section Two-One is on Page~\pageref{Two-One}\par
Section Two-Two is on Page~\pageref{Two-Two}\par
Section Two-Three is on Page~\pageref{Two-Three}\par
Section Three-One is on Page~\pageref{Three-One}\par


\bigskip
Using the \textbf{cleveref package (V0.18)}:\par
\bigskip
See \cpageref{One-One,One-Two,Three-One}\par
See \cpageref{One-One,One-Two,Two-One,Two-Two,Three-One}\par
See \cpagerefrange{One-One}{Three-One}\par
\end{document}