sub continued_fraction { my ($a, $b, $n) = (@_[0,1], $_[2] // 100); #<========= what is $_[2] // 100 ?? $a->() + ($n && $b->() / continued_fraction($a, $b, $n-1)); } printf "√2 ≈ %.9f\n", continued_fraction do { my $n; sub { $n++ ? 2 : 1 } }, sub { 1 }; # <===== Note there is no third arg passed printf "e ≈ %.9f\n", continued_fraction do { my $n; sub { $n++ || 2 } }, do { my $n; sub { $n++ || 1 } }; # <===== Note there is no third arg passed printf "π ≈ %.9f\n", continued_fraction do { my $n; sub { $n++ ? 6 : 3 } }, do { my $n; sub { (2*$n++ + 1)**2 } }, 1_000; #<==== Here there is a 3rd arg printf "π/2 ≈ %.9f\n", continued_fraction do { my $n; sub { 1/($n++ || 1) } }, sub { 1 }, 1_000; #<==== Here there is a 3rd arg