Depends. Each recursive call to function places another entry on the system stack. So it's possible to 'crash the stack' if you get stuck in a loop.

Some problems are best suited for recursion - like traversing a file system. You don't know how many levels you will descend, so leave that up to recursion.

The same problem can be solved with a while loop, but only if you implement your own stack.

Keep in mind that the faster solution (in general - always exceptions) will be a loop, and for that matter, if you can find a formula to replace the loop, then you will really increase the speed.

Example, summing a list of consecutive numbers, starting with 1: 

my @numbs = qw(1 2 3 4 5 6 7 8 9 10);

# loop style
sub loop {

    my $numbs = shift;
    my $sum;

    map { $sum += $_; } @{$numbs};
    return $sum;
}

# recursive style - warning: destroys array
sub recurse {

    my ($numbs, $sum) = @_;

    if (scalar @{$numbs}) {
        $sum += pop @{$numbs};
        &recurse($numbs, $sum);
    }
    else {
        return $sum;
    }

}

[download]
Both are trivial for this example - and execute in about the same time: 
Benchmark: timing 100000 iterations of Loop, Recursive...
     Loop:  1 wallclock secs ( 0.70 usr +  0.00 sys =  0.70 CPU)
Recursive:  1 wallclock secs ( 0.68 usr +  0.00 sys =  0.68 CPU)

[download]
But, a relatively famous person by the name of Gauss will tell you that this problem can be solved in one fell swoop with: 

Benchmark: timing 100000 iterations of Guass...
    Guass:  1 wallclock secs ( 0.49 usr +  0.00 sys =  0.49 CPU)

[download]

Thanks to myocom and FouRPlaY for help on the Gauss formula.

In reply to (jeffa) Re: Recursion by jeffa
in thread Recursion by lolindrath

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