Module Nothing

module Nothing: sig .. end

An uninhabited type.

This is useful when interfaces require that a type be specified, but the implementer knows this type will not be used in their implementation of the interface.

For instance, Async.Std.Rpc.Pipe_rpc.t is parameterized by an error type, but a user may want to define a Pipe RPC that can't fail.

type t = Nothing0.t

val unreachable_code : t -> 'a

Because there are no values of type Nothing.t, a piece of code that has a value of type Nothing.t must be unreachable. In such an unreachable piece of code, one can use unreachable_code to give the code whatever type one needs. For example:

      let f (r : (int, Nothing.t) Result.t) : int =
        match r with
        | Ok i -> i
        | Error n -> Nothing.unreachable_code n
      ;;

include Identifiable.S

It may seem weird that this is identifiable, but we're just trying to anticipate all the contexts in which people may need this. It would be a crying shame if you had some variant type involving Nothing.t that you wished to make identifiable, but were prevented for lack of Identifiable.S here.

Obviously, of_string and t_of_sexp will raise an exception.

module Stable: sig .. end