elmish-update-exception-bug.fsx

#r "nuget: Elmish"

open Elmish

type Msg =
    | Do
    | Done of int
    | Error of exn

let init _ = 0, Cmd.ofMsg Do

let update msg state =
    match msg with
    | Do -> 
        printfn "Do"
        // this correctly raise exception
        //state, Cmd.ofMsg (Done state) 
        // exception is not raised for Cmd.OfAsync.* functions
        state, Cmd.OfAsync.either (fun x -> async { return x + 1 }) state Done Error
    | Done i -> 
        failwith "BOOM"
        printfn "Done: %i" i
        i, Cmd.none
    | Error e -> 
        printfn "Error: %A" e
        state, Cmd.none

let view _ _ = ()

Program.mkProgram init update view
|> Program.withConsoleTrace
|> Program.run

printfn "Exception was not raised"