What is wrong with this Akka.NET code?

Question

I spent some time searching for the Akka.NET F# API. Could not find it, even though there is good C# documentation. I found the code below, dated March 2017, which looks good, but unfortunately generates an exception when I try to run it.

Two questions:

1) What is wrong with the code below?

2) Is there online documentation for the Akka.Net F# API and if yes, where is it?

Observation: I tried several other F# Akka.NET snippets I found online and all of them generated exceptions.

The URL for the code is:

https://www.seventeencups.net/building-a-mud-with-f-sharp-and-akka-net-part-one/

And here is the code I tried to run:

open System
open Akka.Actor
open Akka.Configuration
open Akka.Remote
open Akka.FSharp

let system = System.create "system" (Configuration.defaultConfig())

type GreeterMsg =
    | Hello of string
    | Goodbye of string

let greeter = spawn system "greeter" <| fun mailbox ->
    let rec loop() = actor {
        let! msg = mailbox.Receive()

        match msg with
        | Hello name -> printf "Hello, %s!\n" name
        | Goodbye name -> printf "Goodbye, %s!\n" name

        return! loop()
    }
    loop()

The exception message includes the following:

System.TypeLoadException: Method 'WatchWith' in type '-ctor@270' from assembly 'Akka.FSharp, Version=1.2.3.41, Culture=neutral, PublicKeyToken=null' does not have an implementation

Answer 1

WatchWith method has been introduced in Akka.NET v1.3, while you're using Akka.FSharp v1.2.3. You'll need to downgrade your Akka dependency back to 1.2.3 (at this point in time Akka.FSharp is not yet available in v1.3).