if I write a recursive procedure like factorial_iterative ... does it's memory usage grow linearly the way factorial_recursive looks like it should.
Yep, since it's just a wrapper around a recursive sub, fi_helper. Recursion isn't terribly efficient in perl since function calls aren't too swift and take up a fair bit of memory (hence the recusion warning (see. perldiag)). An iterative approach however will be a bit quicker e.g 
use strict;

use Benchmark 'cmpthese';

my $limit = @ARGV ? shift : 100;

cmpthese(-10, {
    recurse => sub { rec($limit) },
    iterate => sub { itr($limit) },
});

sub rec {
  my $n = shift;
  return $n == 1 ? return 1 : $n * rec($n - 1);
}
sub itr {
    my($n, $r) = (shift, 1);
    $r *= $n-- while $n > 1;
    return $r;
}

__output__

Benchmark: running iterate, recurse for at least 10 CPU seconds...
   iterate: 11 wallclock secs (10.58 usr +  0.00 sys = 10.58 CPU) @ 58
+14.45/s (n=61546)
   recurse: 11 wallclock secs (10.23 usr +  0.00 sys = 10.23 CPU) @ 16
+77.45/s (n=17162)
          Rate recurse iterate
recurse 1677/s      --    -71%
iterate 5814/s    247%      --

[download]
Of course all benchmarks are to be taken with a grain of salt, but I think this gives a pretty clear illustration of the hit recursion incurs.
HTH

_________
broquaint

In reply to Re: Re: Re: Iterative vs Recursive Processes by broquaint
in thread Iterative vs Recursive Processes by mvaline

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