ocaml-containers/actionMan.ml

(*
copyright (c) 2013, simon cruanes
all rights reserved.

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modification, are permitted provided that the following conditions are met:

redistributions of source code must retain the above copyright notice, this
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*)

(** {6 Action Language for command line} *)

module Action = struct
  type trigger = string

  type _ t =
    | Return : 'a -> 'a t
    | Bind : 'a t * ('a -> 'b t) -> 'b t
    | Ignore : ('a t * 'b t) -> 'b t
    | Any : string t
    | ReadInt : (int -> 'a t) -> 'a t
    | ReadString : (string -> 'a t) -> 'a t
    | ReadBool : (bool -> 'a t) -> 'a t
    | Choice : 'a t list -> 'a t
    | Fail : string -> 'a t

  let return x = Return x
  
  let (>>=) x f = Bind (x, f)

  let (>>) x f = Bind (x, (fun _ -> f ()))

  let ( *>) a b = Ignore (a, b)

  let ignore x = x *> return ()

  let any = Any

  let accept trigger =
    Any >>= fun x ->
      if x = trigger
        then return ()
        else Fail ("expected trigger \"" ^ trigger ^ "\"")

  let with_string ?trigger f =
    match trigger with
    | None -> ReadString f
    | Some t -> accept t *> ReadString f

  let with_int ?trigger f =
    match trigger with
    | None -> ReadInt f
    | Some t -> accept t *> ReadInt f

  let with_bool ?trigger f =
    match trigger with
    | None -> ReadBool f
    | Some t -> accept t *> ReadBool f

  let choice l = Choice l

  let repeat act =
    let rec try_next acc =
      choice
        [ act >>= (fun x -> try_next (x::acc))
        ; return acc
        ]
    in
    (try_next []) >>= (fun l -> return (List.rev l))

  let opt act =
    choice [ act >>= (fun x -> return (Some x)); return None ]
    
  let fail msg = Fail msg
end

type 'a result =
  | Ok of 'a
  | Error of string

type 'a partial_result =
  | POk of 'a * int   (* value and position in args *)
  | PError of string  (* error message *)

let parse_args args (act : 'a Action.t) : 'a result =
  let module A = Action in
  (* interpret recursively, with backtracking. Returns partial result *)
  let rec interpret : type a. string array -> int -> a Action.t -> a partial_result
  = fun args i act ->
    let n = Array.length args in
    match act with
    | A.Return x -> POk (x, i)
    | A.Bind (x, f) ->
      begin match interpret args i x with
      | POk (x, i') -> interpret args i' (f x)
      | PError msg -> PError msg
      end
    | A.Ignore (a, b) ->
      begin match interpret args i a with
      | POk (_, i') -> interpret args i' b
      | PError msg -> PError msg
      end
    | A.Any when i >= n -> mk_error i "expected [any], reached end"
    | A.Any -> POk (args.(i), i+1)
    | A.ReadInt f when i >= n -> mk_error i "expected [int], reached end"
    | A.ReadInt f ->
      begin try
        let j = int_of_string args.(i) in
        interpret args (i+1) (f j)
      with Failure _ -> mk_error i "expected [int]"
      end
    | A.ReadString _ when i >= n -> mk_error i "expected [string], reached end"
    | A.ReadString f -> interpret args (i+1) (f args.(i))
    | A.ReadBool _ -> failwith "not implemented: read bool" (* TODO *)
    | A.Fail msg -> mk_error i msg
    | A.Choice l -> try_choices args i [] l
  (* try the actions remaining in [l], whenre [errors] is the list
      of errors in already tried branches *)
  and try_choices : type a. string array -> int -> string list -> a Action.t list -> a partial_result 
  = fun args i errors l ->
    match l with
    | [] ->
      let msg = Printf.sprintf "choice failed: [%s]" (String.concat " | " errors) in
      mk_error i msg
    | act::l' ->
      begin match interpret args i act with
      | POk _ as res -> res   (* success! *)
      | PError msg ->
        try_choices args i (msg :: errors) l'
      end
  (* report error *)
  and mk_error : type a. int -> string -> a partial_result
  = fun i msg ->
    PError (Printf.sprintf "at arg %d: %s" i msg)
  in
  match interpret args 1 act with
  | POk (x,_) -> Ok x
  | PError msg -> Error msg

let parse act = parse_args Sys.argv act

let print_doc oc act =
  failwith "print_doc: not implemented"