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(************************************************************************)
(* * The Coq Proof Assistant / The Coq Development Team *)
(* v * INRIA, CNRS and contributors - Copyright 1999-2018 *)
(* <O___,, * (see CREDITS file for the list of authors) *)
(* \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. *)
exception IsNone
(** [has_some x] is [true] if [x] is of the form [Some y] and [false]
otherwise. *)
val has_some : 'a option -> bool
(** Negation of [has_some] *)
val is_empty : 'a option -> bool
(** [equal f x y] lifts the equality predicate [f] to
option types. That is, if both [x] and [y] are [None] then
it returns [true], if they are both [Some _] then
[f] is called. Otherwise it returns [false]. *)
val equal : ('a -> 'a -> bool) -> 'a option -> 'a option -> bool
(** Same as [equal], but with comparison. *)
val compare : ('a -> 'a -> int) -> 'a option -> 'a option -> int
(** Lift a hash to option types. *)
val hash : ('a -> int) -> 'a option -> int
(** [get x] returns [y] where [x] is [Some y].
@raise IsNone if [x] equals [None]. *)
val get : 'a option -> 'a
(** [make x] returns [Some x]. *)
val make : 'a -> 'a option
(** [bind x f] is [f y] if [x] is [Some y] and [None] otherwise *)
val bind : 'a option -> ('a -> 'b option) -> 'b option
(** [init b x] returns [Some x] if [b] is [true] and [None] otherwise. *)
val init : bool -> 'a -> 'a option
(** [flatten x] is [Some y] if [x] is [Some (Some y)] and [None] otherwise. *)
val flatten : 'a option option -> 'a option
(** [append x y] is the first element of the concatenation of [x] and
[y] seen as lists. In other words, [append (Some a) y] is [Some
a], [append None (Some b)] is [Some b], and [append None None] is
[None]. *)
val append : 'a option -> 'a option -> 'a option
(** {6 "Iterators"} *)
(** [iter f x] executes [f y] if [x] equals [Some y]. It does nothing
otherwise. *)
val iter : ('a -> unit) -> 'a option -> unit
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].
@raise Heterogeneous otherwise. *)
val iter2 : ('a -> 'b -> unit) -> 'a option -> 'b option -> unit
(** [map f x] is [None] if [x] is [None] and [Some (f y)] if [x] is [Some y]. *)
val map : ('a -> 'b) -> 'a option -> 'b option
(** [fold_left f a x] is [f a y] if [x] is [Some y], and [a] otherwise. *)
val fold_left : ('b -> 'a -> 'b) -> 'b -> 'a option -> 'b
(** [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].
@raise Heterogeneous otherwise. *)
val fold_left2 : ('a -> 'b -> 'c -> 'a) -> 'a -> 'b option -> 'c option -> 'a
(** [fold_right f x a] is [f y a] if [x] is [Some y], and [a] otherwise. *)
val fold_right : ('a -> 'b -> 'b) -> 'a option -> 'b -> 'b
(** [fold_left_map f a x] is [a, f y] if [x] is [Some y], and [a] otherwise. *)
val fold_left_map : ('a -> 'b -> 'a * 'c) -> 'a -> 'b option -> 'a * 'c option
(** Same as [fold_left_map] on the right *)
val fold_right_map : ('b -> 'a -> 'c * 'a) -> 'b option -> 'a -> 'c option * 'a
(** [cata f e x] is [e] if [x] is [None] and [f a] if [x] is [Some a] *)
val cata : ('a -> 'b) -> 'b -> 'a option -> 'b
(** {6 More Specific Operations} *)
(** [default a x] is [y] if [x] is [Some y] and [a] otherwise. *)
val default : 'a -> 'a option -> 'a
(** [lift] is the same as {!map}. *)
val lift : ('a -> 'b) -> 'a option -> 'b option
(** [lift_right f a x] is [Some (f a y)] if [x] is [Some y], and
[None] otherwise. *)
val lift_right : ('a -> 'b -> 'c) -> 'a -> 'b option -> 'c option
(** [lift_left f x a] is [Some (f y a)] if [x] is [Some y], and
[None] otherwise. *)
val lift_left : ('a -> 'b -> 'c) -> 'a option -> 'b -> 'c option
(** [lift2 f x y] is [Some (f z w)] if [x] equals [Some z] and [y] equals
[Some w]. It is [None] otherwise. *)
val lift2 : ('a -> 'b -> 'c) -> 'a option -> 'b option -> 'c option
(** {6 Smart operations} *)
module Smart :
sig
(** [Smart.map f x] does the same as [map f x] except that it tries to share
some memory. *)
val map : ('a -> 'a) -> 'a option -> 'a option
end
(** {6 Operations with Lists} *)
module List : sig
(** [List.cons x l] equals [y::l] if [x] is [Some y] and [l] otherwise. *)
val cons : 'a option -> 'a list -> 'a list
(** [List.flatten l] is the list of all the [y]s such that [l] contains
[Some y] (in the same order). *)
val flatten : 'a option list -> 'a list
(** [List.find f l] is the first [f a] different from [None],
scrolling through elements [a] of [l] in left-to-right order;
it is [None] if no such element exists. *)
val find : ('a -> 'b option) -> 'a list -> 'b option
(** [List.map f [a1;...;an]] is the list [Some [b1;...;bn]] if
for all i, there is a [bi] such that [f ai] is [Some bi]; it is
[None] if, for at least one i, [f ai] is [None]. *)
val map : ('a -> 'b option) -> 'a list -> 'b list option
end
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