Thank you - that looks extremely promising. I really, really like that it uses a call-back to get the dependancies rather than asking for a complete list of dependancies up front. Since S::T has to loop through everything anyway, why loop through it in the calling code, too, when a callback will implicitly perform the loop?

It does seem to perform the sort in the reverse order of what I wanted, but thankfully perl makes that pretty darned trivial.

For posterity, my example has changed to:

use Sort::Topological;

use strict;
use Data::Dumper;

my %before =
    (
     a => _s(qw(c)),
     b => _s(qw(d e)),
     c => _s(qw(l)),
     d => _s(qw(e a)),
     e => _s(qw(c)),
     f => _s(qw(g d)),
     g => _s(qw(c)),
     h => _s(qw(g i)),
     i => _s(qw()),
     j => _s(qw(c)),
     k => _s(qw()),
     l => _s(qw()),
     n => _s(qw(c)),
     o => _s(qw()),
    );

# print Dumper(\%before);

my @order = reverse
    Sort::Topological::toposort(
                                sub {
                                    @{$before{$_[0]}};
                                },
                                [ keys %before ],
                               );

print "@order\n";

sub _s
{
    [ @_ ]; #my %h = map { $_ => 1 } @_;
    #\%h
}
[download]

And the result is:

l c a e i g d o f b h k j n
[download]

At this point, this (simple) example is working. Which gives me reasonable confidence since I did manage to create a non-working example in the first place. Again, thanks!

The only issue is that the module drags in too much - too bad it wasn't separated out into its own distribution. Oh well, can't win 'em all!