It seems you have some solutions, so I'm taking a different tack. Two points:

1) You'd probably benefit more from showing us a little code with your question, before seeing the solutions.

2) You may want to look at Memoize, like so: 

use Memoize;
# make sure memoize happens before p is called
BEGIN { memoize('p'); }

[download]
Or, cache it yourself: 
{ # closure for sub p

  my %seen;

  sub p
  {
    my $arg_string = join '^', @_;
    return $seen{$arg_string} if exists $seen{$arg_string};

    # compute $result here as usual
    # ...

    return $seen{$arg_string} = $result;
  } # end sub p

} # end closure for sub p

[download]
I leave it to you to work out how to handle the empty parameter list :)

Update: See BrowserUk's Re^2: recursive formula. below for reasons why this isn't a good idea.

-QM
--
Quantum Mechanics: The dreams stuff is made of

In reply to Re: recursive formula. by QM
in thread recursive formula. by BioGeek

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