Cannot bind port to port (Dezyne Reference Manual)

11.12.4 Cannot bind port to port

The directions of the left and right port mentioned in the binding do not match. The following constructs are allowed:

When binding a port of the system to a port of a component instance, the directions must be the same:
- provides binds to provides
- requires binds to requires
When binding a port of the system to another port of the system Component, the directions must be the opposite:
- provides binds to requires or vice versa.
When binding a port of a component instance to a port of another (or the same) component instance, the directions must be the opposite:
- provides binds to requires or vice versa.

interface ihello
{
  in bool hello ();
  behavior {on hello:{}}
}

component hello
{
  provides ihello p;
  requires ihello r;
  behavior {}
}

component world
{
  provides ihello p;
  behavior {}
}

component instance_port_not_bound
{
  provides ihello p;
  system
  {
    hello h;
    world w;
    p <=> h.r;
    h.p <=> w.p;
  }
}

This results in the following error messages:

binding-mismatch-direction.dzn:27:5: error: cannot bind provides port
    `p' to requires port `r'
binding-mismatch-direction.dzn:22:3: info: port `p' defined here
binding-mismatch-direction.dzn:10:3: info: port `r' defined here
binding-mismatch-direction.dzn:28:5: error: cannot bind provides port
    `p' to provides port `p'
binding-mismatch-direction.dzn:16:3: info: port `p' defined here
binding-mismatch-direction.dzn:9:3: info: port `p' defined here