let rec f=function|'!'::t->1-f t|'0'::[]->0|_->1

​

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

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

​

let test (input,expected) = 

  let result = input |> Seq.toList |> f

  if result = expected then

    printfn "%s = %d" input result

  else

    printfn "Error at %s" input

​

[

  ("0", 0)

  ("1", 1)

  ("0!", 1)

  ("1!", 1)

  ("!0", 1)

  ("!1", 0)

  ("!0!", 0)

  ("!1!", 0)

  ("0!!", 1)

  ("1!!", 1)

  ("!!0", 0)

  ("!!1", 1)

  ("!0!!", 0)

  ("!!!1", 0)

  ("!!!0!!!!", 0)

  ("!!!1!!!!", 0)

] |> Seq.iter test