#
# This software is Copyright 2005 by Elsevier Inc.  You may use it
# under the terms of the license at http://perl.plover.com/hop/LICENSE.txt .
#



###
### check_move
###

## Chapter 1 section 3

@position = (' ', ('A') x 3); # Disks are all initially on peg A

sub check_move {
  my $i;
  my ($disk, $start, $end) = @_;
  if ($disk < 1 || $disk > $#position) {
    die "Bad disk number $disk. Should be 1..$#position.\n";
  }
  unless ($position[$disk] eq $start) {
    die "Tried to move disk $disk from $start, but it is on peg $position[$disk].\n";
  }
  for $i (1 .. $disk-1) {
    if ($position[$i] eq $start) {
      die "Can't move disk $disk from $start because $i is on top of it.\n";
    } elsif ($position[$i] eq $end) {
      die "Can't move disk $disk to $end because $i is already there.\n";
    }
  }
  print "Moving disk $disk from $start to $end.\n";
  $position[$disk] = $end;
}