package earley

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This library provide a type Container.t, which can be used as a list of polymorphic references.

Another way to see it, is map with access time in O(N) where N is the number of tables! Note: O(1) is possible, but usually there are very few table at the same time.

The typical use case is to have a record with a field of type Container.t. Then when you want to store some information in that field of type a, you create with Container.create_table, a value of type a Container.table. The with Container.add and Container.find, you can store value in your field of type Container.t.

More precisely, consider the following type for oriented graphs:

type node = { name: string;
              mutable next: node list;
              ptrs : Container.t }
type graph = node list (* at least on node per component *)

If you want to traverse the graphe, you create a table to associate a boolean to each note:

let iter graph f =
  let visited : bool Container.table = Container.create_table 101 in
  ....
  (* the table is automatically freed when visited is collected *)

If you want to compute the distance between two nodes:

let distance a b =
  let distance_to_a : int Container.table = Container.create_table 101 in
  ....

The functorial interface is useful when you have a parametric type. Considier a record type 'a t to which you want to associate values of type ('b,'a) v . It is enough for this to call the functor with

module M = Constainer.Make(struct type ('a,'b) v end)

and have a field of type 'a M.container inside your record. Then, you use the type 'b M.table when you want to start to associate values of type ('a,'b) v to the record. The same module M can be used for many types 'b .

Remark: the non funtorial version is just defined by: Container.Make(struct type ('a, 'b) elt = 'a end

type t

Type of a container cell

type 'a table

Type of a container table. You must create a container table of type a table to store value of type a in a container cell. Many table can have the same type, the value are associated to the pair (cell, table), not just to the cell.

val create : unit -> t

create () creates a new container cell

val add : 'a table -> t -> 'a -> unit

add tab cell v associates the value v to the pair (tab, cell). complexity if O(N) where N is the number of tables with a value associated to this cell.

val find : 'a table -> t -> 'a

find tab cell return the value associated to (tab, cell). raises Not_found if the are no such value

val clear : 'a table -> unit

clear tab removed all value associated to a table.

val create_table : unit -> 'a table

create_table () creates a new table

type _ tag = ..

GADT to represent types in the syntax (extended when needed).

val address : t -> unit tag

address n return a unique id of each cell

type ('a, 'b) eq =
  1. | Y : ('a, 'a) eq
  2. | N : ('a, 'b) eq

Standard eq-type.

module type Param = sig ... end
val eq : t -> t -> bool
module Make (T : sig ... end) : Param with type ('a, 'b) elt = ('a, 'b) T.elt
type ('a, 'b) elt = 'a
type 'a iter = {
  1. f : 'b. ('a, 'b) elt -> unit;
}
val iter : 'a iter -> 'a table -> unit
type ('a, 'c) fold = {
  1. f : 'b. ('a, 'b) elt -> 'c -> 'c;
}
val fold : ('a, 'c) fold -> 'a table -> 'c -> 'c
module Ref : Param with type ('a, 'b) elt = 'b
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