contract Foo {
    function Foo() {}

    function chop() public returns (bytes32)
    {
        return "Chop!!!";
    }
}

contract Bar {
    // Foo bytecode will be compiled into Bar's bytecode
    Foo public foo = new Foo();

    // Foo bytecode will be loaded into memory from an existing Foo deployment
    Foo public foo2 = Foo(0xF00BAA...);

    // An address primitive to cast;
    address public hoo;

    // Internal calls can pass complex types
    function kungFoo(Foo sumFoo) internal {
        sumFoo.chop();
    }

    // External calls ca pass basic types
    function kungHoo(address sumHoo) public {
        hoo = sumHoo;
        Foo(hoo).chop();
    }
}