//const:
[<Literal>]
let notImportantString= "blahBlah"
let mutable COUNT = 1.0

//funcs:
//addNumber --> add the sequence number COUNT to each file.
let addNumber (file : string)  =
 let mutable str = File.ReadAllText(file)
 printfn "%s" str//just for check
 let num = COUNT.ToString()
 let str4 = str + " " + num + "nnn DONE"
 COUNT <- COUNT + 1.0
 let str2 =  File.WriteAllText(file,str4)
 file

//matchFunc --> check if is ".txt"
let matchFunc (file : string) =
 file.Contains(".txt")

//allFiles --> go through all files of a given dir
let allFiles dir =

seq
    { for file in Directory.GetFiles(dir) do
        yield file
           }

////////////////////////////

let dir = "D:FSharpTesting"
let a = allFiles dir
         |> Seq.filter(matchFunc)
         |> Seq.map(addNumber)
printfn "%A" a

let a = allFiles dir
     |> Seq.filter(matchFunc)
     |> Seq.map(addNumber)
     |> Seq.iter ignore   // Forces the sequence to execute

module Counter =
  let mutable count = 1

open Counter
count <- count + 1

let count =
  let i = ref 0
  fun () ->
    incr i
    !i

let one = count()
let two = count()

var lazyseq = "abcdef".Select(a => print a); //does not do anything
    var b = lazyseq.ToArray(); //will evaluate the sequence

let isNebraskaCity_bad city =
    let cities =
        printfn "Creating cities Set"
        ["Bellevue"; "Omaha"; "Lincoln"; "Papillion"]
        |> Set.ofList

    cities.Contains(city)

let isNebraskaCity_good =
    let cities =
        printfn "Creating cities Set"
        ["Bellevue"; "Omaha"; "Lincoln"; "Papillion"]
        |> Set.ofList

    fun city -> cities.Contains(city)