[MirageOS-devel] Irmin RW store questions

[KC Sivaramakrishnan <sk826@xxxxxxxxxxxx>]

I’d like to use Irmin RW store to implement a simple timestamp based last-writer-wins register. While the type of Irmin.AO_MAKER = functor (K : Irmin.Hash.S) (V : Tc.S0) -> … is understandable, the type of Irmin.RW_MAKER = (K : Irmin.Hum.S) (V : Irmin.Hash.S) -> … is not intuitive. Why is the type of K and V not the same as in AO_MAKER? Why should the type of value be a Hash.S?

I also witness surprising behaviour for any non-string keys with Git memory backend. See the code below. Are there any restrictions with the use of RW stores?

(* Build with

 * ocamlfind ocamlc -linkpkg -package irmin.git,irmin.unix,git -o rw_test rw_test.ml

 *)

let (>>=) = Lwt.bind

module Git = Irmin_git.RW(Git.Memory)

module HumInt = struct

  include Tc.Int

  let of_hum s = 

    (* Following line prints “master" *)

    print_string @@ s^"\n";

    int_of_string s

  let to_hum = string_of_int

end

module HumString = struct

  include Tc.String

  let of_hum s = s 

  let to_hum s = s 

end

(*****************************************************************************)

(* Following Fails *)

module Hum = HumInt

let key = 0 

(* Following works *)

(*

module Hum = HumString

let key = "0"

*)

(*****************************************************************************)

module S = Git(Hum)(Irmin.Hash.SHA1)

module SHA1 = Irmin.Hash.SHA1

let conf = Irmin_git.config ()

let task = Irmin_unix.task

let main =

  S.create conf task

  >>= fun store ->

      S.update (store "update") key 

      (SHA1.of_hum "2fd4e1c67a2d28fced849ee1bb76e7391b93eb12")

  >>= fun _ -> S.read_exn (store "read") key 

  >>= fun res ->

        SHA1.to_hum res |> print_string;

        Lwt.return ()

let () = Lwt_main.run main

Thanks

KC

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