samples for getting Fibonacci function from closure function.

fib2.pl

#!/usr/bin/perl

use strict;
use warnings;

sub get_fib_with_initvals {
    my ($first, $second) = @_;
    # Perl の代入は右結合なので、 my $fib = sub { ... } で右辺に $fib があってはいけない。
    # この場合、宣言と代入を分けて書く必要がある
    my $fib;
    $fib = sub {
        my $n = shift;
        die "argument is required as digit" if !is_digit($n);

        if ( $n == 0 ) {
            return 0;
        } elsif ( $n == 1 ) {
            return $first;
        } elsif ( $n == 2 ) {
            return $second;
        } else {
            return $fib->($n-1) + $fib->($n-2); # 再帰呼び出し
        }
    };
    return $fib;
}

sub is_digit {
    my $arg = shift;
    if ( defined $arg && $arg =~ /^\d+$/ ) {
        return 1;
    } else {
        return;
    }
}

my $fib = get_fib_with_initvals(7, 11);

for my $i (1..10) {
    printf "%d: %d\n", $i, $fib->($i);
}

fib2.rb

#!/usr/bin/ruby

def get_fib_with_initvals(first, second)
  # Ruby の代入は単純な右結合ではない
  fib = lambda do |n|
    raise "argument is required as digit" if !n.kind_of?(Integer)

    if n == 0
      return 0
    elsif n == 1
      return first
    elsif n == 2
      return second
    else
      return fib.call(n-1) + fib.call(n-2)
    end
  end
  fib
end

fib = get_fib_with_initvals(7, 11)

(1..10).each do |i|
  printf "%d: %d\n", i, fib.call(i)
end

output.txt

1: 7
2: 11
3: 18
4: 29
5: 47
6: 76
7: 123
8: 199
9: 322
10: 521