In F#, class constructors can be declared in several different ways. To declare a non-static class, one usually defines a primary constructor, plus zero or more additional constructors. To declare a static class, one usually defines a module. Using a Primary Constructor In F#, it is possible to create a thread-safe singleton with just three lines of code: /// A public thread-safe singleton class in F#, /// using a private primary constructor. type Singleton private() = static let instance = Singleton()[...]