Module Bus.Callback_arity

Callback_arity states the type of callbacks stored in a bus. Using Callback_arity is an implementation technique that allows callbacks to be defined as ordinary n-ary curried functions (e.g., a1 -> a2 -> a3 -> r), instead of forcing n-ary-variadic callbacks to use tuples (e.g., a1 * a2 * a3 -> r). This also avoids extra allocation.

When reading the bus interface, keep in mind that each 'callback is limited, through create, to the types exposed by the variants in Callback_arity.