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
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
|
# OCaml {#sec-language-ocaml}
## User guide {#sec-language-ocaml-user-guide}
OCaml libraries are available in attribute sets of the form `ocaml-ng.ocamlPackages_X_XX` where X is to be replaced with the desired compiler version. For example, ocamlgraph compiled with OCaml 4.12 can be found in `ocaml-ng.ocamlPackages_4_12.ocamlgraph`. The compiler itself is also located in this set, under the name `ocaml`.
If you don't care about the exact compiler version, `ocamlPackages` is a top-level alias pointing to a recent version of OCaml.
OCaml applications are usually available top-level, and not inside `ocamlPackages`. Notable exceptions are build tools that must be built with the same compiler version as the compiler you intend to use like `dune` or `ocaml-lsp`.
To open a shell able to build a typical OCaml project, put the dependencies in `buildInputs` and add `ocamlPackages.ocaml` and `ocamlPackages.findlib` to `nativeBuildInputs` at least.
For example:
```nix
let
pkgs = import <nixpkgs> {};
# choose the ocaml version you want to use
ocamlPackages = pkgs.ocaml-ng.ocamlPackages_4_12;
in
pkgs.mkShell {
# build tools
nativeBuildInputs = with ocamlPackages; [ ocaml findlib dune_2 ocaml-lsp ];
# dependencies
buildInputs = with ocamlPackages; [ ocamlgraph ];
}
```
## Packaging guide {#sec-language-ocaml-packaging}
OCaml libraries should be installed in `$(out)/lib/ocaml/${ocaml.version}/site-lib/`. Such directories are automatically added to the `$OCAMLPATH` environment variable when building another package that depends on them or when opening a `nix-shell`.
Given that most of the OCaml ecosystem is now built with dune, nixpkgs includes a convenience build support function called `buildDunePackage` that will build an OCaml package using dune, OCaml and findlib and any additional dependencies provided as `buildInputs` or `propagatedBuildInputs`.
Here is a simple package example.
- It defines an (optional) attribute `minimalOCamlVersion` (see note below)
that will be used to throw a descriptive evaluation error if building with
an older OCaml is attempted.
- It uses the `fetchFromGitHub` fetcher to get its source.
- It also accept `duneVersion` parameter (valid value are `"1"`, `"2"`, and
`"3"`). The recommended practice it to set only if you don't want the default
value and/or it depends on something else like package version. You might see
a not-supported argument `useDune2`. The behavior was `useDune2 = true;` =>
`duneVersion = "2";` and `useDune2 = false;` => `duneVersion = "1";`. It was
used at the time when dune3 didn't existed.
- It sets the optional `doCheck` attribute such that tests will be run with
`dune runtest -p angstrom` after the build (`dune build -p angstrom`) is
complete, but only if the Ocaml version is at at least `"4.05"`.
- It uses the package `ocaml-syntax-shims` as a build input, `alcotest` and
`ppx_let` as check inputs (because they are needed to run the tests), and
`bigstringaf` and `result` as propagated build inputs (thus they will also be
available to libraries depending on this library).
- The library will be installed using the `angstrom.install` file that dune
generates.
```nix
{ lib,
fetchFromGitHub,
buildDunePackage,
ocaml,
ocaml-syntax-shims,
alcotest,
result,
bigstringaf,
ppx_let }:
buildDunePackage rec {
pname = "angstrom";
version = "0.15.0";
minimalOCamlVersion = "4.04";
src = fetchFromGitHub {
owner = "inhabitedtype";
repo = pname;
rev = version;
hash = "sha256-MK8o+iPGANEhrrTc1Kz9LBilx2bDPQt7Pp5P2libucI=";
};
checkInputs = [ alcotest ppx_let ];
buildInputs = [ ocaml-syntax-shims ];
propagatedBuildInputs = [ bigstringaf result ];
doCheck = lib.versionAtLeast ocaml.version "4.05";
meta = {
homepage = "https://github.com/inhabitedtype/angstrom";
description = "OCaml parser combinators built for speed and memory efficiency";
license = lib.licenses.bsd3;
maintainers = with lib.maintainers; [ sternenseemann ];
};
}
```
Here is a second example, this time using a source archive generated with `dune-release`. It is a good idea to use this archive when it is available as it will usually contain substituted variables such as a `%%VERSION%%` field. This library does not depend on any other OCaml library and no tests are run after building it.
```nix
{ lib, fetchurl, buildDunePackage }:
buildDunePackage rec {
pname = "wtf8";
version = "1.0.2";
minimalOCamlVersion = "4.02";
src = fetchurl {
url = "https://github.com/flowtype/ocaml-${pname}/releases/download/v${version}/${pname}-v${version}.tbz";
hash = "sha256-d5/3KUBAWRj8tntr4RkJ74KWW7wvn/B/m1nx0npnzyc=";
};
meta = {
homepage = "https://github.com/flowtype/ocaml-wtf8";
description = "WTF-8 is a superset of UTF-8 that allows unpaired surrogates";
license = lib.licenses.mit;
maintainers = [ lib.maintainers.eqyiel ];
};
}
```
The build will automatically fail if two distinct versions of the same library
are added to `buildInputs` (which usually happens transitively because of
`propagatedBuildInputs`). Set `dontDetectOcamlConflicts` to true to disable this
behavior.
|
