#!/usr/bin/perl -w
use strict;
use warnings;


sub make_rand {
    my $x = 0;
    return sub {
        return $x++; # not very random
    };
}

my $rng = make_rand();

for my $i (1..4) {
    my $x = $rng->();
    print "$x\n";
}

##</code><code>##

#!/usr/bin/perl -w
use strict;
use warnings;

sub NEXTVAL { $_[0]->() }

sub make_rand {
    my $x = 0;
    return sub {
        return $x++;
    };
}

my $rng = make_rand();

for my $i (1..4) {
    my $x = NEXTVAL ( $rng );
    print "$x\n";
}

##</code><code>##

#!/usr/bin/perl -w
use strict;
use warnings;

sub NEXTVAL { $_[0]->() }
sub Iterator { return $_[0] }

sub make_rand {
    my $x = 0;
    return sub {
    return Iterator sub {
        return $x++;
    };
}

my $rng = make_rand();

for my $i (1..4) {
    my $x = NEXTVAL ( $rng );
    print "$x\n";
}

##</code><code>##

#!/usr/bin/perl -w
use strict;
use warnings;

sub NEXTVAL { $_[0]->() }
sub Iterator (&) { return $_[0] }

sub make_rand {
    my $x = 0;
    return Iterator {
        return $x++;
    };
}

my $rng = make_rand();

for my $i (1..4) {
    my $x = NEXTVAL ( $rng );
    print "$x\n";
}