use strict;
use warnings;

# This function takes a "range string" and returns
# a list that can be used in a Perl array slice.
# Some examples should clarify:
# Range string    Return list
#    "4"          (4)
#    "4-6"        (4,5,6)
#    "5-"         (5,6,7,...,$maxind)
#    "-2"         (0,1,2)
sub range_to_list
{
   my $maxind = shift;    # max index of (zero-based) list
   my $range  = shift;    # a "range string" (see examples above)
   my @ilist = split /-/, $range, 2;
   my $nlist = @ilist;
   $nlist == 1 || $nlist == 2 or die "range_to_list $nlist out of range";
   if ( $nlist == 1 )
   {
      $ilist[0] =~ /^\d+$/ or die "range_to_list, '$ilist[0]' not numeric";
      $ilist[0] <= $maxind or die "range_to_list, '$ilist[0]' out of range";
      return @ilist;
   }
   if ( $ilist[0] eq '' )    # e.g. "-5" case
   {
      $ilist[1] =~ /^\d+$/ or die "range_to_list, '$ilist[1]' not numeric";
      $ilist[1] <= $maxind or die "range_to_list, '$ilist[1]' out of range";
      return ( 0 .. $ilist[1] );
   }
   if ( $ilist[1] eq '' )    # e.g. "3-" case
   {
      $ilist[0] =~ /^\d+$/ or die "range_to_list, '$ilist[0]' not numeric";
      $ilist[0] <= $maxind or die "range_to_list, '$ilist[0]' out of range";
      return ( $ilist[0] .. $maxind );
   }
   # e.g. "3-5" case
   $ilist[0] =~ /^\d+$/ or die "range_to_list, '$ilist[0]' not numeric";
   $ilist[1] =~ /^\d+$/ or die "range_to_list, '$ilist[1]' not numeric";
   return ( $ilist[0] .. $ilist[1] );
}

my $maxind = 10;
print "maxind=$maxind\n";
for my $rstr ( "x",  "1-2-3", "0",   "10",  "11", "4",   "4-6",
               "7-", "-2",    "-10", "-11", "-0", "10-", "11-" )
{
   print "rstr:$rstr:";
   my @ret;
   eval { @ret = range_to_list( $maxind, $rstr ) };
   if ($@)
   {
      print "...exc:$@";
   }
   else
   {
      print "...ret:@ret:\n";
   }
}
my @apples = ( ":zero:", ":one:", ":two:", ":three:", ":four:" );
print "apples ", @apples[range_to_list( $#apples, "1-3" )], "\n";