Quelle option.ml Sprache: SML

(************************************************************************)
(*         *      The Rocq Prover / The Rocq Development Team           *)
(*  v      *         Copyright INRIA, CNRS and contributors             *)
(* <O___,, * (see version control and CREDITS file for authors & dates) *)
(*   \VV/  **************************************************************)
(*    //   *    This file is distributed under the terms of the         *)
(*         *     GNU Lesser General Public License Version 2.1          *)
(*         *     (see LICENSE file for the text of the license)         *)
(************************************************************************)

(** Module implementing basic combinators for OCaml option type.
   It tries follow closely the style of OCaml standard library.

   Actually, some operations have the same name as [List] ones:
   they actually are similar considering ['a option] as a type
   of lists with at most one element. *)

(** [has_some x] is [true] if [x] is of the form [Some y] and [false]
    otherwise.  *)
let has_some = function
  | None -> false
  | _ -> true

let is_empty = function
  | None -> true
  | Some _ -> false

(** Lifting equality onto option types. *)
let equal f x y = match x, y with
  | None, None -> true
  | Some x, Some y -> f x y
  | _, _ -> false

let compare f x y = match x, y with
  | None, None -> 0
  | Some x, Some y -> f x y
  | None, Some _ -> -1
  | Some _, None -> 1

let hash f = function
  | None -> 0
  | Some x -> f x

exception IsNone

(** [get x] returns [y] where [x] is [Some y].
    @raise IsNone if [x] equals [None]. *)
let get = function
  | Some y -> y
  | _ -> raise IsNone

(** [make x] returns [Some x]. *)
let make x = Some x

(** [bind x f] is [f y] if [x] is [Some y] and [None] otherwise *)
let bind x f = match x with Some y -> f y | None -> None

let filter f x = bind x (fun v -> if f v then x else None)

(** [init b x] returns [Some x] if [b] is [true] and [None] otherwise. *)
let init b x =
  if b then
    Some x
  else
    None

(** [flatten x] is [Some y] if [x] is [Some (Some y)] and [None] otherwise. *)
let flatten = function
  | Some (Some y) -> Some y
  | _ -> None

(** [append x y] is the first element of the concatenation of [x] and
    [y] seen as lists. *)
let append o1 o2 =
  match o1 with
  | Some _ -> o1
  | None  -> o2

(** {6 "Iterators"} ***)

(** [iter f x] executes [f y] if [x] equals [Some y]. It does nothing
    otherwise. *)
let iter f = function
  | Some y -> f y
  | _ -> ()

exception Heterogeneous

(** [iter2 f x y] executes [f z w] if [x] equals [Some z] and [y] equals
    [Some w]. It does nothing if both [x] and [y] are [None]. And raises
    [Heterogeneous] otherwise. *)
let iter2 f x y =
  match x,y with
  | Some z, Some w -> f z w
  | None,None -> ()
  | _,_ -> raise Heterogeneous

(** [map f x] is [None] if [x] is [None] and [Some (f y)] if [x] is [Some y]. *)
let map f = function
  | Some y -> Some (f y)
  | _ -> None

(** [fold_left f a x] is [f a y] if [x] is [Some y], and [a] otherwise. *)
let fold_left f a = function
  | Some y -> f a y
  | _ -> a

(** [fold_left2 f a x y] is [f z w] if [x] is [Some z] and [y] is [Some w].
    It is [a] if both [x] and [y] are [None]. Otherwise it raises
    [Heterogeneous]. *)
let fold_left2 f a x y =
  match x,y with
  | Some x, Some y -> f a x y
  | None, None -> a
  | _ -> raise Heterogeneous

(** [fold_right f x a] is [f y a] if [x] is [Some y], and [a] otherwise. *)
let fold_right f x a =
  match x with
  | Some y -> f y a
  | _ -> a

(** [fold_left_map f a x] is [a, f y] if [x] is [Some y], and [a] otherwise. *)
let fold_left_map f a x =
  match x with
  | Some y -> let a, z = f a y in a, Some z
  | _ -> a, None

let fold_right_map f x a =
  match x with
  | Some y -> let z, a = f y a in Some z, a
  | _ -> None, a

(** [cata f a x] is [a] if [x] is [None] and [f y] if [x] is [Some y]. *)
let cata f a = function
  | Some c -> f c
  | None -> a

(** {6 More Specific operations} ***)

(** [default a x] is [y] if [x] is [Some y] and [a] otherwise. *)
let default a = function
  | Some y -> y
  | _ -> a

(** {6 Smart operations} *)

module Smart =
struct

  (** [Smart.map f x] does the same as [map f x] except that it tries to share
      some memory. *)
  let map f = function
    | Some y as x -> let y' = f y in if y' == y then x else Some y'
    | _ -> None

end

(** {6 Operations with Lists} *)

module List =
struct
  (** [List.cons x l] equals [y::l] if [x] is [Some y] and [l] otherwise. *)
  let cons x l =
    match x with
    | Some y -> y::l
    | _ -> l

  (** [List.flatten l] is the list of all the [y]s such that [l] contains
      [Some y] (in the same order). *)
  let rec flatten = function
    | x::l -> cons x (flatten l)
    | [] -> []

  let map f l =
    let rec aux f l = match l with
    | [] -> []
    | x :: l ->
      match f x with
      | None -> raise_notrace Exit
      | Some y -> y :: aux f l
    in
    try Some (aux f l) with Exit -> None

end

quality100%

¤ Dauer der Verarbeitung: 0.1 Sekunden (vorverarbeitet) ¤

Wurzel

Suchen

Beweissystem der NASA

Beweissystem Isabelle

NIST Cobol Testsuite

Cephes Mathematical Library

Wiener Entwicklungsmethode

Haftungshinweis

Die Informationen auf dieser Webseite wurden nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit, noch Qualität der bereit gestellten Informationen zugesichert.

Bemerkung:

Die farbliche Syntaxdarstellung ist noch experimentell.