#!/usr/bin/perl
use v5.14;
use strict;
use warnings;

my $result  = 0;
my $level   = 2;		# next is F2
my $max_val = 4_000_000;
my $max_rec = 1000;

my $DBG = 1;


fib(1,0);			# F1,F0
print $result;


sub fib
{
    my  @frame = @_;

    #my $DBG = 1;

    unshift @frame, $frame[0] + $frame[1];   # prepend next level Fib (see footnote 1)
    pop @frame;                              # remove tailing Fib (optional)

    count($frame[0]);

    say "Fib(" . $level++ . ") =  $frame[0]" if $DBG;
    say " ... # \@frame = (@frame)" if $DBG;

    # playing safe with deep recursion    
    die "May recursion $max_rec exceeded" if $level > $max_rec; 

    return fib(@frame) unless($frame[0] >= $max_val);
}

sub count {
    my ($increment) = @_;

    #my $DBG = 1;
    
    if(($increment  % 2) == 0){
	say "adding Fib($level) = $increment to $result" if $DBG;
	$result += $increment;
    }
}

##</code><code>##

Compilation started at Tue Jul 29 22:14:14

perl /home/lanx/perl/pm/euler_problem_2.pl
Fib(2) =  1
 ... # @frame = (1 1)
adding Fib(3) = 2 to 0
Fib(3) =  2
 ... # @frame = (2 1)
Fib(4) =  3
 ... # @frame = (3 2)
Fib(5) =  5
 ... # @frame = (5 3)
adding Fib(6) = 8 to 2
Fib(6) =  8
 ... # @frame = (8 5)
Fib(7) =  13
 ... # @frame = (13 8)
Fib(8) =  21
 ... # @frame = (21 13)
adding Fib(9) = 34 to 10
Fib(9) =  34
 ... # @frame = (34 21)
Fib(10) =  55
 ... # @frame = (55 34)
Fib(11) =  89
 ... # @frame = (89 55)
adding Fib(12) = 144 to 44
Fib(12) =  144
 ... # @frame = (144 89)
Fib(13) =  233
 ... # @frame = (233 144)
Fib(14) =  377
 ... # @frame = (377 233)
adding Fib(15) = 610 to 188
Fib(15) =  610
 ... # @frame = (610 377)
Fib(16) =  987
 ... # @frame = (987 610)
Fib(17) =  1597
 ... # @frame = (1597 987)
adding Fib(18) = 2584 to 798
Fib(18) =  2584
 ... # @frame = (2584 1597)
Fib(19) =  4181
 ... # @frame = (4181 2584)
Fib(20) =  6765
 ... # @frame = (6765 4181)
adding Fib(21) = 10946 to 3382
Fib(21) =  10946
 ... # @frame = (10946 6765)
Fib(22) =  17711
 ... # @frame = (17711 10946)
Fib(23) =  28657
 ... # @frame = (28657 17711)
adding Fib(24) = 46368 to 14328
Fib(24) =  46368
 ... # @frame = (46368 28657)
Fib(25) =  75025
 ... # @frame = (75025 46368)
Fib(26) =  121393
 ... # @frame = (121393 75025)
adding Fib(27) = 196418 to 60696
Fib(27) =  196418
 ... # @frame = (196418 121393)
Fib(28) =  317811
 ... # @frame = (317811 196418)
Fib(29) =  514229
 ... # @frame = (514229 317811)
adding Fib(30) = 832040 to 257114
Fib(30) =  832040
 ... # @frame = (832040 514229)
Fib(31) =  1346269
 ... # @frame = (1346269 832040)
Fib(32) =  2178309
 ... # @frame = (2178309 1346269)
adding Fib(33) = 3524578 to 1089154
Fib(33) =  3524578
 ... # @frame = (3524578 2178309)
Fib(34) =  5702887
 ... # @frame = (5702887 3524578)
4613732
Compilation finished at Tue Jul 29 22:14:14