An example of parallelism in F#.

fsharp_webclient_run_async_parallelism.fs

open System
open System.IO
open System.Net
open System.Web
open System.Collections.Generic
open System.Text.RegularExpressions


let urls =["https://en.wikipedia.org/wiki/Toomas_Altnurme"; "https://en.wikipedia.org/wiki/J%C3%BCri_Arrak"; "https://en.wikipedia.org/wiki/Alisa_Jakobi"; 
"https://en.wikipedia.org/wiki/Kalli_Kalde"; "https://en.wikipedia.org/wiki/Liis_Koger"; "https://en.wikipedia.org/wiki/Mari_Kurismaa"; 
"https://en.wikipedia.org/wiki/Malle_Leis"; "https://en.wikipedia.org/wiki/Olav_Maran"; "https://en.wikipedia.org/wiki/Peeter_Mudist";
"https://en.wikipedia.org/wiki/Navitrolla"; "https://en.wikipedia.org/wiki/Mall_Nukke"; "https://en.wikipedia.org/wiki/Evald_Okas";
"https://en.wikipedia.org/wiki/Enno_Ootsing"; "https://en.wikipedia.org/wiki/Tiit_P%C3%A4%C3%A4suke"; "https://en.wikipedia.org/wiki/Avo_Paistik";
"https://en.wikipedia.org/wiki/Aapo_Pukk"; "https://en.wikipedia.org/wiki/Martin_Saar"; "https://en.wikipedia.org/wiki/Mart_Sander"; 
"https://en.wikipedia.org/wiki/Erik_Schmidt_(painter)"; "https://en.wikipedia.org/wiki/Eugen_Sterpu"; "https://en.wikipedia.org/wiki/Viive_Sterpu";
"https://en.wikipedia.org/wiki/Olev_Subbi"; "https://en.wikipedia.org/wiki/Helge_Uuetoa"; "https://en.wikipedia.org/wiki/%C3%9Clo_Vilimaa";
"https://en.wikipedia.org/wiki/Aili_Vint"; "https://en.wikipedia.org/wiki/Mare_Vint"; "https://en.wikipedia.org/wiki/Toomas_Vint"]

let basePath = @"C:\FILES\JSON\"

let writeFile (filePath:string, fileContent:string) =
    let encoding = System.Text.Encoding.UTF8 
    let rr = File.OpenWrite(filePath) 
    use writer = new IO.StreamWriter(rr,encoding)  
    writer.Write(fileContent)

let fetchUrl(url:string) = 
    async{    
    try
    ServicePointManager.SecurityProtocol <- SecurityProtocolType.Tls12 ||| SecurityProtocolType.Tls11
    use webClient = new WebClient()    
    let! downloadedJson = webClient.AsyncDownloadString(Uri(url))
    return downloadedJson    
    with error -> return "Error"
    }

let writeJson(content:string)=
      try
      let converted = Regex.Unescape(content)
      let mytitle = Guid.NewGuid().ToString()
      let newPath = basePath+mytitle+".json"
      writeFile(newPath,converted)   
      with e -> printfn "FAILURE: %s" e.Message

let handleDocument (uri:string)= 
        let title = uri.Replace("https://en.wikipedia.org/wiki/","") 
        let newUrl = "https://en.wikipedia.org/w/api.php?action=query&format=json&titles="+title+"&prop=extracts"
        newUrl

let myFunc = 
    let jsUrls = urls |> Seq.take 20 |> Seq.map(fun uri -> handleDocument uri)
    let tasks = [for url in jsUrls -> fetchUrl(url)  ]   
    let parallelTasks = Async.Parallel tasks
    let str:string[] = Async.RunSynchronously parallelTasks
    str |> Array.iter(fun content -> writeJson content)
    ()

[<EntryPoint>]
let main argv = 
    myFunc   
    System.Console.ReadKey() |> ignore
    0