#!/usr/bin/perl

use strict;
use warnings;

my $beholder_default = 'beholder';
my $param = get_param();

my %monster_lookup = (
  'beholder' => {
    book => 'Monstrous Manual',
    beholder => 1,
    page => 21,
  },
  'death kiss' => {
    book => 'Monstrous Manual',
    beholder => 0,
    page => 21,
  },
);

# this saves duplicating data in your code
my @monsters = keys %monster_lookup;


my $monster;
if ($param){
  $monster = $beholder_default;
}
else{
  my $rand = int rand @monsters;
  $monster = $monsters[$rand];
}

my $book     = $monster_lookup{$monster}{book};
my $page     = $monster_lookup{$monster}{page};
my $beholder = $monster_lookup{$monster}{beholder};

if (not $beholder){
  print "$monster ";
}
print "beholder ($book, pg $page)\n";

sub get_param {
  # get your input from somewhere
  my $param = 0;
  return $param;
}