DPrint.fs

let rec mkKn (ty: System.Type) =
    if Reflection.FSharpType.IsFunction(ty) then
        let _, ran = Reflection.FSharpType.GetFunctionElements(ty)
        // NOTICE: do not delay `mkKn` invocation until runtime
        let f = mkKn ran
        Reflection.FSharpValue.MakeFunction(ty, fun _ -> f)
    else
        box ()

let dprint (v: bool) (fmt: Printf.TextWriterFormat<'a>) : 'a =
  if v then
    printfn fmt
  else
    unbox<'a> (mkKn typeof<'a>)

[<Sealed>]
type Format<'T> private () =
    static let instance : 'T =
        unbox (mkKn typeof<'T>)
    static member Instance = instance

let dprint2 verbose args =
    if verbose then
        printfn args
    else
        Format<_>.Instance

#time

for i in 0 .. 10000 do
    dprint false "%i" i // 1 sec

for i in 0 .. 10000 do
    dprint2 false "%i" i // 0.001 sec