use strict;
use warnings;

use Math::Combinatorics;

# Probably best to get stopwords from a file, but for testing:
my @stopwords = qw/ the of in on with by and /;
my %stop_hash = map { $_ => 1 } @stopwords;

my $term = 'Programming Perl, by Wall, Christiansen and Orwant';
my @term = grep { not $stop_hash{lc $_} } split ' ', $term;

# Default highlighting combination: n-1 from n (3 from 4, 5 from 6..)
my $n_from = shift || @term - 1; 

my @combos = combine( $n_from, @term );

my $result = highlight( \@combos, $term );
print join "\n", @$result; 

sub highlight {
  my $to_highlight = shift;
  my $term = shift;

  my @highlighted;
  foreach my $combo ( @$to_highlight ) {
    my $str = $term;

    # Highlight with Caps for console output
    # $str =~ s/$_/<em>$_</em>/ for @$combo;
    $str =~ s/$_/\U$_/ for @$combo;

    push @highlighted, $str;
  }
  return \@highlighted;
}