aFunc.fs

let aFunction myParamFunc =
	myParamFunc()

AMethod.cs

class A {
static void AMethod(MyBase myBase) {
    myBase.AMemberMethod();
}
}

calla.cs

MyBase myBase = new MyBase();
A.AMethod(myBase);

calla2.cs

MyDerived myDerived = new MyDerived ();
A.AMethod(myDerived);

IAMethod.cs

class A {
static void AMethod(IMyInterface myInterface) {
    myInterface.AMemberMethod();
}
}