vblt.org
forked from
gazagnaire.org/irmin
Persistent store with Git semantics: lazy reads, delayed writes, content-addressing
1(** Persistent pointers to OCaml values.
2
3 Links delimit serialization boundaries in data structures. Insert [v] calls
4 to control persistence granularity - only new links are written.
5
6 {[
7 type tree = node t
8 and node = Empty | Node of { l : tree; x : int; r : tree }
9
10 let rec add s x t =
11 match get t with
12 | Empty -> v s (Node { l = v s Empty; x; r = v s Empty })
13 | Node n ->
14 if x = n.x then t
15 else if x < n.x then v s (Node { n with l = add s x n.l })
16 else v s (Node { n with r = add s x n.r })
17 ]}
18
19 Properties: [get (v s x) = x] and [equal (v s (get l)) l]. *)
20
21(** {1:types Types} *)
22
23type 'a t
24(** The type for links to ['a] values. Links embed their content store. *)
25
26type 'a store
27(** The type for stores with root of type ['a]. *)
28
29type address
30(** The type for content addresses. Opaque. *)
31
32(** {1:links Links} *)
33
34val v : _ store -> 'a -> 'a t
35(** [v s x] is a link to [x], using content store from [s]. *)
36
37val of_address : _ store -> address -> 'a t
38(** [of_address s addr] is a link that lazily loads from [addr]. *)
39
40val get : 'a t -> 'a
41(** [get l] is the value linked by [l]. Fetches if needed. *)
42
43val address : 'a t -> address
44(** [address l] is the content address of [l]. Writes if needed. *)
45
46val equal : 'a t -> 'a t -> bool
47(** [equal l0 l1] is [true] iff [l0] and [l1] have the same address. *)
48
49val is_val : 'a t -> bool
50(** [is_val l] is [true] if the value is in memory (like {!Lazy.is_val}). *)
51
52val pp : Format.formatter -> 'a t -> unit
53(** [pp] formats the link's address (or ["<mem>"] if not yet stored). *)
54
55(** {1:stores Stores} *)
56
57val read : 'a store -> 'a
58(** [read s] is the current root of [s]. Raises if no root set. *)
59
60val write : 'a store -> 'a -> unit
61(** [write s x] sets the root of [s] to [x]. *)
62
63val is_open : _ store -> bool
64(** [is_open s] is [true] if [s] is open. *)
65
66val close : _ store -> unit
67(** [close s] closes [s]. Further operations raise. *)
68
69(** {2 Store creation} *)
70
71module Make (_ : Codec.S) : sig
72 val v : unit -> _ store
73 (** [v ()] is a new in-memory store. *)
74end
75
76module Git : sig
77 val v : unit -> _ store
78 (** [v ()] is a new in-memory Git-compatible store (SHA-1). *)
79end
80
81module Mst : sig
82 val v : unit -> _ store
83 (** [v ()] is a new in-memory MST store (SHA-256, ATProto). *)
84end