Source file readable_printer.ml

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module R =
struct
    type e =
      | String of string * int * int (* start, beyond *)
      | Char of char
      | Fill of int * char

    type t =
      | More of e * (unit -> t)
      | Done

    let has_more (r:t): bool =
      r <> Done

    let peek (r: t): char =
        match r with
        | Done ->
           assert false (* Illegal call! *)

        | More (e, _) ->
            match e with
            | String (s, pos, beyond) ->
                assert (pos < beyond);
                s.[pos]
            | Char c ->
                c
            | Fill (n, c) ->
                assert (0 < n);
                c

    let advance (r: t): t =
        match r with
        | Done ->
            assert false (* Illegal call! *)

        | More (e,f) ->
            match e with
            | String (s, pos, beyond) ->
                assert (pos < beyond);
                if pos + 1 = beyond then
                   f ()
                else
                    More (String (s, pos+1, beyond), f)

            | Char _ ->
                f ()

            | Fill (n,c) ->
                assert (0 < n);
                if n = 1 then
                    f ()
                else
                    More (Fill (n-1, c), f)


    let make_substring
        (s: string)
        (start: int)
        (len: int)
        (f: unit -> t): t
        =
        assert (0 <= start);
        assert (0 <= len);
        assert (start + len <= String.length s);
        if len = 0 then
            f ()
        else
            More (String (s, start, start + len), f)


    let make_char (c:char) (f:unit -> t): t =
        More (Char c, f)


    let make_fill (n:int) (c:char) (f:unit -> t): t =
        if n = 0 then
            f ()
        else
            More (Fill(n,c), f)

    let make_empty: t =
        Done
end








module M =
struct
    type 'a t =
        ('a -> R.t) -> R.t

    let return (a:'a) (k:'a -> R.t): R.t =
        k a

    let (>>=) (m:'a t) (f:'a -> 'b t) (k:'b -> R.t): R.t =
        m (fun a -> f a k)
end





type t = unit M.t


let empty: t =
    M.return ()


let (<+>)  (p1: t) (p2: t): t =
    M.(p1 >>= fun _ -> p2)


let string (s:string): t =
    R.make_substring s 0 (String.length s)


let substring (s: string) (start: int) (len: int) : t =
    R.make_substring s start len


let fill (n: int) (c: char): t =
    assert (0 <= n);
    R.make_fill n c


let char (c: char): t =
    R.make_char c


let readable (m: unit M.t): R.t =
    m (fun () -> R.make_empty)