The cartesian function returns the Cartesian Product. The Cartesian Product is the combination of all possible values.

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my $data =
    Seq::cartesian(
        Seq->wrap(qw/clubs spades hearts diamond/),
        Seq->wrap(qw/7 8 9 10 B D K A/),
    )->to_array;

Calling to_array will evaluate the expression and generates the following Perl data-structure.

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[
    ['clubs'  ,'7'],['clubs'  ,'8'],['clubs'  ,'9'],['clubs'  ,'10'],
    ['clubs'  ,'B'],['clubs'  ,'D'],['clubs'  ,'K'],['clubs'  ,'A' ],
    ['spades' ,'7'],['spades' ,'8'],['spades' ,'9'],['spades' ,'10'],
    ['spades' ,'B'],['spades' ,'D'],['spades' ,'K'],['spades' ,'A' ],
    ['hearts' ,'7'],['hearts' ,'8'],['hearts' ,'9'],['hearts' ,'10'],
    ['hearts' ,'B'],['hearts' ,'D'],['hearts' ,'K'],['hearts' ,'A' ],
    ['diamond','7'],['diamond','8'],['diamond','9'],['diamond','10'],
    ['diamond','B'],['diamond','D'],['diamond','K'],['diamond','A' ],
]

The implementation of Seq::cartesian.

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# cartesian : Seq<'a> -> Seq<'b> -> Seq<'a * 'b>
sub cartesian($seqA, $seqB) {
    bind($seqA, sub($a) {
    bind($seqB, sub($b) {
        wrap('Seq', [$a, $b]);
    })});
}

wrap('Seq', [$a, $b]) is the same as Seq->wrap([$a, $b]).

This is how you can implement cartesian in a non-lazy way.

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# cartesian : Array<'a> -> Array<'b> -> Array<'a * 'b>
sub cartesian($arrayA, $arrayB) {
    my @output;
    for my $a ( @$arrayA ) {
        for my $b ( @$arrayB ) {
            push @output, [$a, $b];
        }
    }
    return \@output;
}

and call it.

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my $data =
    cartesian(
        [qw/clubs spades hearts diamond/],
        [qw/7 8 9 10 B D K A/],
    );