You don't need all of those use constant N => 0; either -- the string literal is just as good as a constant.

I'm not clear on this :-)

You have

use constant N  => 0;
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and later

if ($dir == N)     {return (--$r, $c)}
elsif ...
else {
    die "Inside 'step': invalid param\n"
}
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use constant... essentially gives you a subroutine-ish entity (without a sigil). If you miss the constant declaration, you'll be looking for a subroutine definition for N, NE,, etc. Still, some people like this.

The benefits of declaring these constants are:
• difficult to accidentally reassign to constants
• direction validation (with die...)
• saving quotes in comparison (as in  if ( $dir eq "N" ))
[Assuming that $dir is now a string.]

The drawbacks are:
• no obvious sub definition
• constant isn't perfectly constant
• constants aren't interpolated in double quoted strings
[See use constant for a complete rundown.]

I guess what I'm really saying is that it's unfair to compare a literal translation between C and Perl. Each have their idiosynchracies, and will fall short of the "ideal" on some scales.

Someone here could probably write up a Perlish version of this that was easier to follow, easier to maintain, and perhaps did a few nifty tricks to boot. Though it might run slower than C. :)