classage X {

// if not commented out, the following line does not typecheck 
// because the export method and the import method does not conform
// to the subtyping constraints. 
// (They have different types of contravariants).

/*
mixer A {
  import void f(int x) 
  export void f() {}

}
*/

// if not commented out, the following line does not typecheck 
// because the export method and the import method does not conform
// to the subtyping constraints. 
// (They have different types of convariants).

/*
mixer B {
 import void f() 
 export int f() { return 1;}

}
*/

// if not commented out, the following line does not typecheck 
// because the export method and the import method does not conform
// to the subtyping constraints. 
// (The contravariants do not conform to subtyping).

/*
mixer C {
 import void f(Sub2 x) 
 export void f(Sub1 x) { }

}
*/

// if not commented out, the following line does not typecheck 
// because the export method and the import method does not conform
// to the subtyping constraints. 
// (The convariants do not conform to subtyping).

/*
mixer D {
 import Sub1 f() 
 export Sub2 f() { return create Sub2(); }

}
*/


// however, when subtyping is complied, the program does go through.


mixer C {
 import void f(Sub1 x) 
 export void f(Sub2 x) { }

}

mixer D {
 import Sub2 f() 
 export Sub1 f() { return create Sub1(); }

}


// the situation is similar for pluggers.

/*
plugger A {
  import void f(int x) 
  export void f() {}

}
*/

/*
plugger B {
 import void f() 
 export int f() { return 1;}

}
*/

/*
plugger C {
 import void f(Sub2 x) 
 export void f(Sub1 x) { }

}
*/


/*
plugger D {
 import Sub1 f() 
 export Sub2 f() { return create Sub2(); }

}
*/




// We however disallow overriding on connectors. 
// if not commented out, the following line will complain.
/*
connector A {
  import void f() 
  export void f() {}

}
*/


}


classage Sub1 {

  connector E {
	export void a() { return; }
  }

}

classage Sub2 {

  connector E {
	export void a() { return; }
	import void c() 
  }

}