I wrote a regex for Perl 5.6 that does this. It can be modified easily for letters: 
sub list2range {
  local $_ = join ',' => @_;
  s/(\w+)(?:,((??{''.++(my$x=$+)})))+/$1-$+/g;
  return $_;
}

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japhy -- Perl and Regex Hacker

In reply to Re: Humanized lists of numbers by japhy
in thread Humanized lists of numbers by gryphon

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