How to include Akka.net framework for F# in VSCode

Question

I am trying to use Akka.NET for F# in VSCode using this example I found on the internet.

Code

// ActorSayHello.fsx
#time "on"
// #load "Bootstrap.fsx"

open System
open Akka.Actor
open Akka.Configuration
open Akka.FSharp
open Akka.TestKit

// #Using Actor
// Actors are one of Akka's concurrent models.
// An Actor is a like a thread instance with a mailbox. 
// It can be created with system.ActorOf: use receive to get a message, and <! to send a message.
// This example is an EchoServer which can receive messages then print them.

let system = ActorSystem.Create("FSharp")

type EchoServer =
    inherit Actor

    override x.OnReceive message =
        match message with
        | :? string as msg -> printfn "Hello %s" msg
        | _ ->  failwith "unknown message"

let echoServer = system.ActorOf(Props(typedefof<EchoServer>, Array.empty))

echoServer <! "F#!"

system.Shutdown()

But I am getting this error ActorSayHello.fsx(6,6): error FS0039: The namespace or module 'Akka' is not defined.

I have configured ionide plugin in VScode and am able to run F# without Akka.NET. I installed Akka.NET using the following command

dotnet add package Akka.FSharp --version 1.4.10

The library got added automatically added to .fsproj file. This is the output of the command

Any help would be greatly appreciated. Thank you!

Answer 1

Since you are using a script file it doesn't contain any project reference. Instead you can use nuget references directly from the script!

#r "nuget: Akka.FSharp" 
#r "nuget: Akka.TestKit" 

Another caveat that might occur is that F# interactive needs a --langversion:preview flag to be able to use nuget references. Setting "FSharp.fsiExtraParameters": ["--langversion:preview"] in the VSCode settings.json did the trick for me.

And the last bit that I had to change to make it compile was to replace system.Shutdown() with system.Terminate() because Shutdown method was deprecated and removed.

Here is the full listing with changes mentioned above:

// ActorSayHello.fsx
#time "on"
#r "nuget: Akka.FSharp" 
#r "nuget: Akka.TestKit" 
// #load "Bootstrap.fsx"

open System
open Akka.Actor
open Akka.Configuration
open Akka.FSharp
open Akka.TestKit

// #Using Actor
// Actors are one of Akka's concurrent models.
// An Actor is a like a thread instance with a mailbox. 
// It can be created with system.ActorOf: use receive to get a message, and <! to send a message.
// This example is an EchoServer which can receive messages then print them.

let system = ActorSystem.Create("FSharp")

type EchoServer =
    inherit Actor

    override x.OnReceive message =
        match message with
        | :? string as msg -> printfn "Hello %s" msg
        | _ ->  failwith "unknown message"

let echoServer = system.ActorOf(Props(typedefof<EchoServer>, Array.empty))

echoServer <! "F#!"

system.Terminate()

And the result looks like this on my machine:

Real: 00:00:00.000, ЦП: 00:00:00.000, GC gen0: 0, gen1: 0, gen2: 0
namespace FSI_0012.Project

Hello F#!
Real: 00:00:00.007, ЦП: 00:00:00.000, GC gen0: 1, gen1: 0, gen2: 0
val system : ActorSystem = akka://FSharp
type EchoServer =
  class
    inherit Actor
    override OnReceive : message:obj -> unit
  end
val echoServer : IActorRef = [akka://FSharp/user/$a#989929929]
val it : Threading.Tasks.Task