1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
|
open Core
(* Demonstrate the behaviour of folding-style hash functions *)
type result =
| Null
| Elem of int
| Combine of result * result
[@@deriving sexp, compare]
let ( % ) a b = Combine (a, b)
(* Shadow the standard library *)
module Ppx_hash_lib = struct
module Std = struct
module Hash = struct
type hash_value = result
type state = result
let fold_int s x = Combine (s, Elem x)
let get_hash_value = Fn.id
type seed = unit
let create ?seed:_ () = Null
end
module Builtin = struct
let hash_fold_int = Hash.fold_int
end
end
end
open Ppx_hash_lib.Std
open Builtin
module Tree = struct
type t =
| L of int
| N of t * t
[@@deriving hash]
end
let a, b = 100, 200
let node = 1
let leaf = 0
let tree = Tree.(N (L a, L b))
let%test_unit _ =
let v = Tree.hash tree in
(* Note: [%] associates to the left *)
[%test_result: result]
v
~expect:(Null % Elem node % Elem leaf % Elem a % Elem leaf % Elem b)
;;
|
