sub mapn (&@) {
    my ( $callback, $n ) = splice @_, 0, 2;
    map $callback->( splice @_, 0, $n ), 0 .. @_ / $n -1;
}

##</code><code>##

sub mapnz (&@) {
    my ( $callback, $n ) = splice @_, 0, 2;
    my ( $i, $j ) = ( 0 ) x 2;
    map {
        $i = $j;
        $callback->( @_[ $i .. ( $j += $n ) - 1 ] );
    } 0 .. @_ / $n - 1;
}

##</code><code>##

sub mapn (&@) {
    my ( $callback, $n ) = splice @_, 0, 2;
    map {
        $n = @_ if $n > @_;
        $callback->( splice @_, 0, $n );
    } 0 .. @_ / $n - 1;
}

##</code><code>##

sub mapn (&@) {
    my ( $callback, $n ) = splice @_, 0, 2;
    my ( $i, $j ) = ( 0 ) x 2;
    map {
        $i = $j;
        $n = @_ - $i if $i + $n > @_;
        $callback->( @_[ $i .. ( $j += $n ) - 1 ] );
    } 0 .. @_ / $n - 1;
}

##</code><code>##

sub mapnz (&@) {
    my ( $callback, $n ) = splice @_, 0, 2;
    push @_, ( undef ) x ( -@_ % $n );
    map $callback->( splice @_, 0, $n ), 0 .. @_ / $n - 1;
}