Recursion is very elegant in my opinion, but its performance is relatively horrible. Using globals to eliminate recursion gives you a huge gain in performance, but globals are to be equally avoided to foster maintainable code. The other options are to use "regular" lexical variables or those within closures.

We avoid the use of globals because:

But their performance outweighs that cost sometimes. Might there be some middle ground?

I decided to explore the other options a bit, and it appears that globals and lexicals are almost identical in performance and closure performance is only slightly slower.

Here is the test code and its results: 

#!/usr/bin/perl -w
use strict;
use Benchmark qw/:all/;
my $iGlobal;

my $x = 4;

timethese (1000000,
{
'Recursion' => 'Rfactorial(30)',
'Global' => 'Gfactorial(30)',
'Lexical' => 'Lfactorial(30)',
'Closure' => '&{Cfactorial()}(30)',
}
);

# A classic, recursive soulution.
sub Rfactorial {
        my $i = shift;
        return 1 if $i == 0;
        return 1 if $i == 1;
        return $i * Rfactorial($i - 1);
}

# Rewritten to use global variables.
sub Gfactorial {
        $iGlobal = shift;

        return 1 unless $iGlobal > 1;
        my $result = 1;
        while ($iGlobal > 1) {
                $result = $result * $iGlobal;
                $iGlobal--;
        }
        return $result;
}

# expressed with lexicals
sub Lfactorial {
        my $iLexical = shift;

        return 1 unless $iLexical > 1;
        my $result = 1;
        while ($iLexical > 1) {
                $result = $result * $iLexical;
                $iLexical--;
        }
        return $result;
}


# Rewritten to use closures

sub Cfactorial {
        my $iClosure;
        return sub {
                my $iClosure = shift;
                my $result = 1;
                while ($iClosure > 1) {
                        $result = $result * $iClosure;
                        $iClosure --;
                }
                return $result;
        }
}

[download]
and the results 
Benchmark: timing 1000000 iterations of Closure, Global, Lexical, Recu
+rsion...
   Closure: 66 wallclock secs (61.70 usr +  0.00 sys = 61.70 CPU) @ 16
+207.46/s (n=1000000)
    Global: 62 wallclock secs (58.39 usr +  0.00 sys = 58.39 CPU) @ 17
+126.22/s (n=1000000)
   Lexical: 63 wallclock secs (58.55 usr +  0.00 sys = 58.55 CPU) @ 17
+079.42/s (n=1000000)
 Recursion: 208 wallclock secs (176.95 usr +  0.00 sys = 176.95 CPU) @
+ 5651.31/s (n=1000000)

[download]
I take from the tests is that recoding a recursive routine to use lexicals is, overall, a better option than globals. Closures would give great gains too, but I can't think of an example in which they provide functionality beyond a simple, lexical arrangement.

Do the other monks have more insight?

update (broquaint): changed <pre> tags to <code> tags around the Benchmark result

Edit by tye, add READMORE

In reply to Recursion Alternatives? by Cabrion

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