CommandBus.fs

module CommandBus =
    let createCommandRouter handlers =
        let event = Event<Command>()
        handlers |> List.iter(fun handler -> event.Publish |> Event.add handler)

    let agent = MailboxProcessor.Start(fun inbox ->
        let loop() = async {
            let! cmd = inbox.Receive()
            cmd |> event.Trigger
            return! loop() }
        loop())

    { new IRounter<Command> with
        member __.Send (cmd: Command) =
            cmd |> agent.Post }

CommandData.fs

type Issuer =
    | System
    | User of username: string

    override this.ToString() =
        match this with
        | System -> "System"  // Replace "System" with what ever you'd like
        | User name -> name

type CommandData = { EntityId: Guid; Issuer: Issuer }
type Command = { Data: CommandData; Body: obj }

DomainStartup.fs

open Simple.Web.StructureMap

type DomainStartup() =
    inherit StructureMapStartupBase()

    let commandRouter =
        [ MyDomain.createHandler1;
          MyDomain.createHandler2;
          MyDomain.createHandler3; ]
        |> CommandBus.createCommandRouter

    override __.Configure(config) =
        config.For(typedefof<IRouter<Command>>).Singleton().Use(commandRouter) |> ignore

IRouter.fs

type IRouter<'a> =
    abstract Send: 'a -> unit