Compile-time checking of format specifications

format_checking.fs

// https://sharplab.io/#v2:DYLgZgzgNAJiDUAfYBTALgAhgewPpgEsVgYMwBbTANwwF4BYAKAxYwAcAnAgOzTG7KUMVJkwDaAHgCivDgE8ACth5oAfAF0mqTOQCGPDLjpNWWPIWKkARAFICVjFYASxYNgwB1bBxJWTrAGU5CDQUcgA6AGFsbghsVHCAJRRdGAAZHhQACgBKDERVDAIAc25vFH8WAAYMAHpajA50AFcOAV0BFRRilA4MFAAPAkwAY2wYCsYgA==
// https://dotnetfiddle.net/aUGh3I
let getResult arg =
  let rand = new System.Random()
  let v = (arg * rand.NextDouble()) - 1.0
  v
  
let do_field fmt v =
    printfn fmt v

[<Literal>]
let fmt = "Random Result: %f"

[<EntryPoint>]
let main _ =
  let v = getResult 2.0
  do_field "Random Result: %f" v
  // do_field "%i" "Hello World"
  System.Console.ReadLine() |> ignore
  0 // return an integer exit code

format_checking2.fs

// https://sharplab.io/#v2:DYLgZgzgNAJiDUAfYBTALgAhgewPpgEsVgYMwBbTANwwF4BYAKAxYwAcAnAgOzTG7KUMVJkwDaAHgCivDgE8ACth5oAfAF0mqTOQCGPDLjpNWWPIWKkARAFICVjFYASxYNgwB1bBxJWTrAGU5CDQUcgA6AGFsbghsVHCAJRRdGAAZHhQACgBKDERVDAIAc25vFH8WAAYMAHpajA50AFcOAV0BFRRilA4MFAAPAkwAY2wYCsYgA==
// https://dotnetfiddle.net/aUGh3I

let do_field fmt v =
    printfn fmt v

[<EntryPoint>]
let main _ =
    do_field "%i" "Hello World"
    System.Console.ReadLine() |> ignore
    0 // return an integer exit code