Question

Want to convert some C# code for RX to F# code.
The following C# code works well:

  var seqNum = Observable.Range(1, 5);
  var seqString = from n in seqNum
                  select new string('*', (int)n);
  seqString.Subscribe(str => { Console.WriteLine(str); });
  Console.ReadKey();

The following is my code in F#:

#light
open System
open System.Collections.Generic
open System.Linq
open System.Reactive
open System.Reactive.Linq
open System.Reactive.Subjects
open System.Threading
open System.IO

let seqNum = Observable.Range(1, 5)
let seqString = from n in seqNum
                select new string('*', (int)n)
Console.ReadLine() |> ignore

But I got the following compiler error:
Error: Unexpected keyword ‘new’ in implementation file

If I deleted the new keyword, I got another error:
Error: Successive arguments should be separated by spaces or tupled, and arguments involving function or method applications should be parenthesized

The “new” keyword are totally different in C# and F#.
Please show me how to do the same job in F#.
Thanks,

Answer 1

Here you go:

open System
open System.IO
open System.Reactive
open System.Reactive.Linq

let seqString = Observable.Range(1,5).Select(fun x -> String.replicate x "*")
using (seqString.Subscribe (fun x -> printfn "%s" x))
    (fun _ -> Console.ReadLine() ) |> ignore

EDIT: As Paul suggested below two last lines can be replaced by simple

seqString.Subscribe (printfn "%s") |> ignore

However, if we want to gracefully unsubscribe from our subscription, but get rid of using in lieu of newer use syntax we may replace last two lines by the following three

do
    use subscription = seqString.Subscribe(printfn "%s")
    Console.ReadLine() |> ignore