functional perl result

result.pl

sub successor($k){
    $k+1;
}

sub natural($k) {
    $k;
}

sub pi($k) {
    8/($k*($k+2));
}

sub cube($k) {
    $k**3;
}

sub pi_succ($k) {
    $k+4;
}
say sum_natural(1000);
say sum(1000,&natural,&successor);


say sum_cube(10);
say sum(10,&cube,&successor);


say sum_pi(2e3);
say sum(2e3,&pi,&pi_succ);