function is not callable using argument types ()

[Suliman via Digitalmars-d-learn]

import std.stdio;
import std.concurrency;

void main()
{
void sp(int i)
{
        receive((int i)
        {
                writeln("i: ", i);
        });
}

        auto r = new Generator!int(
        {
                foreach(i; 1 .. 10)
                        yield(i);
        });

        foreach(e;r)
        {
		sp.send(e); //Error: function app.main.sp (int i) is not 
callable using argument types ()
        }

}


What I am doing wrong? How "receive" can be named? Is it's method 
or what? Why it's without return type?