#!/usr/bin/perl -w
# Author:   Chris Ball <chris@cpan.org>
# Function: Provide a 'compact list' for an array of numbers.
# Also at:  http://printf.net/perl/compact.pl

my @approx = @ARGV;
my ($i, $inrange, $start, $end, $more);

use strict;

# Overview:
#  - Loop through the array.
#  - If the element after current matches (cur+1):
#    -  Extend a range if we're in one.
#    -  Set up a range if we aren't. 
#  - If the element after current _isn't_ (cur+1):
#    - Mark/print the end of a range, or
#    - Print a number on its own if we weren't in a range.
#  - If the element after current just doesn't exist at all:
#    - Finish off a range or number tidily.

map { # Loop through the array, using $_.
    my $cur    = $approx[$_];
    my $next   = $approx[$_+1] if defined $approx[$_+1];

    if ($next) { # Is there an array element after this one?
        if ($next != ($cur + 1)) {
            # If the next element _isn't_ current+1.. 
            if ($inrange) {
                # If we're in a range, it needs to be finished. 
                print "$start-$end,";
                $inrange = 0;
            }
            else {
                # We're not in a range. 
                print "$cur,";
            }
        }
        else {
        # If the next array element is cur+1. 
            if ($inrange) {
                # If we're already in a range, extend it by 1. 
                $end++;
            }
            if (not $inrange) {
                # We're not in a range.  Set start/end/inrange.
                $start   = $approx[$_];
                $end     = $approx[$_+1];
                $inrange = 1;
            }

        }
    }
    else {
        # It's the last element.  Make things look tidy.
        if ($inrange) {
            print "$start-$end\n";
        }
        else {
            print "$cur\n";
        }
    }
} 0..$#approx
# -- end.