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package pacomb
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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 tables 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. Then 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 node:
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 'b t to which you want to associate values of type ('a,'b) 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 'b M.container inside your record. Then, you use the type 'a 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 'a .
Remark: the non funtorial version is just defined by: Container.Make(struct type ('a, 'b) elt = 'a end
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
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.
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
val iter : ('a -> unit) -> 'a table -> unititerator as in List module
val fold : ('a -> 'c -> 'c) -> 'a table -> 'c -> 'cfold as in List module
module type Param = sig ... endfunctorial verstion storing element of type ('a, 'b) elt for container of the 'b and table of type 'a