Hi there, I am developing a new Perl module to bring a lazy Sequence to Perl.

It should provide the functionaly you see in C# LINQ or Java 8 Stream. The origin of those interfaces comes from functional programming. Thus i decided to primarily pick the F# API and port it to Perl.

I already implemented a useful set of functions. Here is an example of the module and what you can do with it. Source code of my Seq Module can be found at GitHub so far.

When i have written more functions and documentation i will release it to CPAN.

First solution

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13


my $fib =
    Seq->concat(
        Seq->wrap(1,1),
        Seq->unfold([1,1], sub($state) {
            my $next = $state->[0] + $state->[1];
            return $next, [$state->[1],$next];
        })
    );

is(
    $fib->take(20)->to_array,
    [1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,1597,2584,4181,6765],
    'First 20 Fibonacci numbers');

Second Solution

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20


# Same Fibonacci as above but unfold does not create a new arrayref on every
# iteration. It changes the $state instead. This way less garbage is created
# and could be potential a little bit faster. But it envolves writing more code.
{
    my $fib =
        Seq->concat(
            Seq->wrap(1,1),
            Seq->unfold([1,1], sub($state) {
                my $next = $state->[0] + $state->[1];
                $state->[0] = $state->[1];
                $state->[1] = $next;
                return $next, $state;
            })
        );

    is(
        $fib->take(20)->to_array,
        [1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,1597,2584,4181,6765],
        'First 20 Fibonacci numbers');
}

Third Solution

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18


# You also can use a hash as a state.
{
    my $fib =
        Seq->concat(
            Seq->wrap(1,1),
            Seq->unfold({x => 1, y => 1}, sub($state) {
                my $next = $state->{x} + $state->{y};
                $state->{x} = $state->{y};
                $state->{y} = $next;
                return $next, $state;
            })
        );

    is(
        $fib->take(20)->to_array,
        [1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,1597,2584,4181,6765],
        'First 20 Fibonacci numbers');
}

Bonus: My concat implementation

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11


# Concatenates a list of Seq into a single Seq
sub concat($class, @iters) {
    my $count = @iters;

    # with no values to concat, return an empty iterator
    return empty('Seq') if $count == 0;
    # one element can be returned as-is
    return $iters[0]    if $count == 1;
    # at least two items
    return reduce { append($a, $b) } @iters;
}