There is no need to do this recursively. In fact, that's the last thing you want to do, since each item requires an additional function call, and only a couple hundred simultaneous function calls are necessary to crash Perl. What you want is something more like:

use strict;
use warnings;

my $r = 0;
$r = {
    rest => $r,
    first => 'c'
};
$r = {
    rest => $r,
    first => 'b'
};
$r = {
    rest => $r,
    first => 'a'
};

print join " ", value($r), scalar value($r);

sub value {
    my $self = $_[0];
    if (wantarray) {
        my @value;
        while ($self) {
            push @value, $self->{'first'};
            $self = $self->{'rest'};
        }
        return @value;
    }
    my $c;
    while ($self) {
        $c++;
        $self = $self->{'rest'};
    }
    return $c;
}
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It might be simpler to just have a master data item with a "length" value, however, since this would require constant time to retrieve rather than linear time, and would allow you to significantly simplify the above function.