#!/usr/bin/perl

use warnings;
use diagnostics;
use strict;

my %opcodes = 
    ('add'=> sub{ print "the add opcode was passed operands: @_\n";
                  print "The opcode reported was add with hex value 4\n";},
     'sub'=> \&opcode_sub,
    );

while (my $instruction = <DATA>)
{
  my ($opcode, @operands) = split (/\s+/, $instruction);
  print "\ninstruction: $opcode  operands: @operands\n";
  
  print "calling $opcode...\n";
  $opcodes{$opcode}->(@operands);  # give some data to subroutine
  #$opcodes{$opcode}->();          # or no args  
}

sub opcode_sub
{
   print "The code for subtract opcode was passed these operands: @_\n";
   print "The opcode reported was add with hex value 5\n";
}

=outputs
instruction: add  operands: 5 6 10
calling add...
the add opcode was passed operands: 5 6 10
The opcode reported was add with hex value 4

instruction: sub  operands: 7 8
calling sub...
The code for subtract opcode was passed these operands: 7 8
The opcode reported was add with hex value 5
=cut

__DATA__
add 5 6 10 
sub 7 8