use strict;
use warnings;
use Stream;

my $increment = sub { $_[ 0 ] + 1 };
my $upfrom2   = Stream::iterate_function( $increment, 2 );
my $primes    = prime_filter( $upfrom2 );

my $n = shift || 1;
print nth_term( $primes, $n ), "\n";

exit 0;

sub nth_term {
  my ( $s, $n ) = @_;
  $s = Stream::tail $s while --$n > 0;
  return Stream::head $s;
}

# a closure factory
sub not_multiple_of {
  my $d = shift;
  return sub { $_[ 0 ] % $d };
}

sub prime_filter {
  my $s = shift;             # a stream
  my $p = Stream::head $s;   # a "simple scalar"
  my $t = Stream::tail $s;   # another stream
  my $not_multiple_of_p = not_multiple_of( $p );

  return
    [
      $p,
      sub {
        prime_filter( &Stream::filter( $not_multiple_of_p, $t ) );
      }
    ];
}