#!/usr/bin/perl --
use strict; use warnings;
use Devel::TraceCalls { Subs => [qw/fib /]};
print fib(5);
sub fib {
  my $n = shift;
  if ($n < 2) { return $n }
  fib($n-2) + fib($n-1);
}
__END__
TRACE: main::fib( 5 )
TRACE: +-main::fib( 3 )
TRACE: | +-main::fib( 1 )
TRACE: | +-main::fib( 2 )
TRACE: | ! +-main::fib( 0 )
TRACE: | ! +-main::fib( 1 )
TRACE: +-main::fib( 4 )
TRACE: | +-main::fib( 2 )
TRACE: | ! +-main::fib( 0 )
TRACE: | ! +-main::fib( 1 )
TRACE: | +-main::fib( 3 )
TRACE: | ! +-main::fib( 1 )
TRACE: | ! +-main::fib( 2 )
TRACE: | ! | +-main::fib( 0 )
TRACE: | ! | +-main::fib( 1 )
5

##</code><code>##

md fib-5
md fib-5\fib-3
md fib-5\fib-3\fib-1
md fib-5\fib-3\fib-2
md fib-5\fib-3\fib-2\fib-0
md fib-5\fib-3\fib-2\fib-1
md fib-5\fib-4
md fib-5\fib-4\fib-2
md fib-5\fib-4\fib-2\fib-0
md fib-5\fib-4\fib-2\fib-1
md fib-5\fib-4\fib-3
md fib-5\fib-4\fib-3\fib-1
md fib-5\fib-4\fib-3\fib-2
md fib-5\fib-4\fib-3\fib-2\fib-0
md fib-5\fib-4\fib-3\fib-2\fib-1

##</code><code>##

fib-5
|-- fib-3
|   |-- fib-1
|   `-- fib-2
|       |-- fib-0
|       `-- fib-1
`-- fib-4
    |-- fib-2
    |   |-- fib-0
    |   `-- fib-1
    `-- fib-3
        |-- fib-1
        `-- fib-2
            |-- fib-0
            `-- fib-1