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1opam-version: "2.0"
2maintainer: "Hannes Mehnert <hannes@mehnert.org>"
3authors: ["Hannes Mehnert <hannes@mehnert.org>"]
4homepage: "https://github.com/hannesm/gmap"
5doc: "https://hannesm.github.io/gmap/doc"
6dev-repo: "git+https://github.com/hannesm/gmap.git"
7bug-reports: "https://github.com/hannesm/gmap/issues"
8license: "ISC"
9depends: [
10 "ocaml" {>= "4.04.2"}
11 "ocamlfind" {build}
12 "ocamlbuild" {build}
13 "topkg" {build}
14 "fmt"
15]
16build: [
17 [ "ocaml" "pkg/pkg.ml" "build" "--pinned" "%{pinned}%" "--tests" "false" ]
18]
19synopsis: "Heterogenous maps over a GADT"
20description: """
21Gmap exposes the functor `Make` which takes a key type (a GADT 'a key) and
22outputs a type-safe Map where each 'a key is associated with a 'a value. This
23removes the need for additional packing.
24
25```OCaml
26type _ k =
27 | A : int k
28 | B : string k
29
30module K = struct
31 type 'a t = 'a k
32
33 let compare : type a b. a t -> b t -> (a, b) Gmap.Order.t = fun t t' ->
34 let open Gmap.Order in
35 match t, t' with
36 | A, A -> Eq | A, _ -> Lt | _, A -> Gt
37 | B, B -> Eq
38
39 let pp : type a. Format.formatter -> a t -> a -> unit = fun ppf t v ->
40 match t, v with
41 | A, x -> Fmt.pf ppf "A %d" x
42 | B, s -> Fmt.pf ppf "B %s" s
43end
44
45module M = Gmap.Make(K)
46
47
48let () =
49 let m = M.empty in
50 ...
51 match M.find A m with
52 | Some x -> Printf.printf "got %d\\n" x
53 | None -> Printf.printf "found nothing\\n"
54```
55
56This is already an exhaustive pattern match: there is no need for another case
57(for the constructor `B`) since the type system knows that looking for `A` will
58result in an `int`.
59
60Motivation came from parsing of protocols which usually specify optional values
61and extensions via a tag-length-value (TLV) mechanism: for a given tag the
62structure of value is different - see for example IP options, TCP options, DNS
63resource records, TLS hello extensions, etc.
64
65Discussing this problem with Justus Matthiesen, we came up with this design. Its
66main difference to Daniel C. Bünzli's [hmap](http://erratique.ch/software/hmap)
67is that in gmap the key-value GADT type must be provided when instantiating the
68functor. In hmap, keys are created dynamically."""
69url {
70 src:
71 "https://github.com/hannesm/gmap/releases/download/0.1.0/gmap-0.1.0.tbz"
72 checksum: [
73 "sha256=971dd65451472fbde6a621ac530f6eb7d6a3f28f983551a63eddd72e163c93ea"
74 "md5=aeea8ba33dc24e13d34d49ba2bd6e55a"
75 ]
76}