OCaml: Difference between revisions

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~~Most packages related to~~ OCaml~~, in particular the~~ OCaml ~~compiler and many libraries, belong to the '''ocamlPackages''' attribute set~~ of ~~nixpkgs~~.

[[File:OCaml Logo.svg|alt=The OCaml logo: an orange background with a white foreground of a camel.|thumb|OCaml logo]]

~~== Findlib, ocamlfind ==~~

According to the official [ocaml.org Ocaml website]:<blockquote>

[Ocaml is]... an industrial-strength functional programming language with an emphasis on expressiveness and safety </blockquote>

OCaml libraries are usually located using [http://projects.camlcity.org/projects/findlib.html findlib] and the associated '''ocamlfind''' tool. These tools are found under the '''ocamlPackages.findlib''' attribute and rely on the '''OCAMLPATH''' environment variable.

== Developping in OCaml with Nix ==

~~A hook~~ in the '''findlib~~'''~~ package will automatically populate this variable with the paths to the other libraries. For instance, when starting a shell with

Most packages related to OCaml, in particular the OCaml compiler and many libraries, belong to the <code>ocamlPackages</code> attribute set of nixpkgs. Tools for OCaml development are, in particular, available:

* the [https://dune.build/ dune] builder;

* the [https://github.com/ocaml/ocaml-lsp OCaml language server];

* the [https://github.com/ocaml-ppx/ocamlformat ocamlformat formatter].

=== Build tooling ===

Modern development in OCaml tend to use <code>dune</code>, a build system dedicated for OCaml projects. Nixpkgs provide a dedicated helper [https://nixos.org/manual/nixpkgs/stable/#sec-language-ocaml-packaging buildDuneProject] to facilitate integration with <code>dune</code>.

An example minimal flake for OCaml development is available below:

{{Code|1=// flake.nix

{

description = "Minimal flake for OCaml projects.";

inputs = {

flake-utils.url = "github:numtide/flake-utils";

nixpkgs.url = "nixpkgs";

};

outputs =

{

self,

flake-utils,

nixpkgs,

...

}:

flake-utils.lib.eachDefaultSystem (

system:

let

pkgs = nixpkgs.legacyPackages.${system};

in

{

packages = {

default =

buildDunePackage {

pname = "My Ocaml Package";

duneVersion = "3";

version = "0.1";

minimalOCamlVersion = "4.14";

installTargets = "all doc";

src = ./.;

nativeBuildInputs = with p; [

dune_3

];

};

devShells = {

default = pkgs.mkShell {

name = "Ocaml development shell environment.";

inputsFrom = [ self.packages.${system}.default ];

packages = with pkgs.ocaml-ng.ocamlPackages; [

ocamlformat

ocaml-lsp

utop

pkgs.gnumake

];

shellHook = ''

echo "Welcome in the devshell."

'';

};

}

);

}|lang=nix}}

<code>nix develop</code> followed by <code>dune init project myproject</code> will drop you in a development shell.

==== Opam ====

OCaml has its own package manager, [https://opam.ocaml.org/ opam]. Trying to use it imperatively with Nix will result in errors. However, <code>opam</code> can generate a <code>.opam</code> file, which can be ingested by tools like [https://github.com/tweag/opam-nix opam-nix] to automatically generate a Nix derivation.

==== Manual build with ocamlc, findlib, ocamlfind ====

OCaml libraries are usually located using [http://projects.camlcity.org/projects/findlib.html findlib] and the associated <code>ocamlfind</code> tool. These tools are found under the <code>ocamlPackages.findlib</code> attribute and rely on the <code>OCAMLPATH</code> environment variable.

A hook in the <code>findlib</code> package will automatically populate this variable with the paths to the other libraries. For instance, when starting a shell with

<code>nix-shell --packages ocamlPackages.findlib ocamlPackages.batteries</code>

will set the ~~'''~~OCAMLPATH~~'''~~ variable so that ~~'''~~ocamlfind~~'''~~ can locate the ~~'''~~batteries~~'''~~ library.

will set the <code>OCAMLPATH</code> variable so that <code>ocamlfind</code> can locate the <code>batteries</code> library.

This hook also sets the <code>CAML_LD_LIBRARY_PATH</code> environment variable that is used for locating the dynamically loaded shared libraries (aka stublibs).

~~This hook also sets the '''CAML_LD_LIBRARY_PATH''' environment variable that is~~ used ~~for locating the dynamically loaded shared libraries~~ (~~aka stublibs~~).

=== Scripting with OCaml ===

OCaml can be used in nix-shell scripts as follows:

#!/usr/bin/env nix-shell

(*

#!nix-shell --pure -i ocaml -p ocaml

*)

~~== Using Emacs ==~~

print_string "Hello world! 🚀 \n";;

</syntaxHighlight>

=== Using Emacs ===

[https://github.com/ocaml/tuareg Tuareg] is an Emacs OCaml mode. It can be installed with

<code>nix-env -iA nixpkgs.emacsPackagesNg.tuareg</code>.

Emacs must be configured to be able to find this package: you may need to add a line like this to your ~~'''~~.emacs~~'''~~ file, somewhere between <code>(require 'package)</code> and <code>(package-initialize)</code>:

Emacs must be configured to be able to find this package: you may need to add a line like this to your <code>.emacs</code> file, somewhere between <code>(require 'package)</code> and <code>(package-initialize)</code>:

(add-to-list 'package-directory-list "~/.nix-profile/share/emacs/site-lisp/elpa")

(add-to-list 'package-directory-list "~/.nix-profile/share/emacs/site-lisp/elpa")

</syntaxHighlight>

There is some more documentation in the [https://github.com/NixOS/nixpkgs/blob/master/pkgs/top-level/emacs-packages.nix nixpkgs sources].

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Beware that merlin is specific to one particular version of OCaml (it won’t work correctly with a compiler of a different version).

To configure Emacs and enable the merlin mode, add the following to your '''.emacs''':

To configure Emacs and enable the merlin mode, add the following to your <code>.emacs</code>:

(add-to-list 'load-path "~/.nix-profile/share/emacs/site-lisp")

(require 'merlin)

(add-hook 'tuareg-mode-hook 'merlin-mode t)

</syntaxHighlight>

Also, a specific variable (<code>merlin-command</code>) of the merlin mode must be overridden (its default is <code>opam</code>):

(custom-set-variables

'(merlin-command "ocamlmerlin")

)

</syntaxHighlight>

~~(add-~~to-~~list~~ '~~load~~-~~path "~/~~.nix-~~profile/share~~/emacs/~~site-lisp")~~

A useful complement to merlin is [https://www.typerex.org/ocp-indent.html '''ocp-indent'''], a customizable tool to indent OCaml code. It can be installed using <code>nix-env -iA nixpkgs.ocamlPackages.ocpIndent</code>. To enable it in Emacs, don’t forget to add the following line to your <code>.emacs</code>:

~~(require 'merlin)~~

~~(add-hook 'tuareg-mode-hook 'merlin-mode t)~~

~~Also, a specific variable~~ ('~~''merlin~~-~~command''') of the merlin mode must be overridden (its default is '''opam'''~~):

(require 'ocp-indent)

</syntaxHighlight>

~~(custom-~~set-~~variables~~

=== Specific version of the OCaml compiler ===

~~'(merlin-command "ocamlmerlin")~~

Various versions of the <code>ocamlPackage</code> attribute set are available, corresponding to various versions of OCaml. For instance, the attribute set <code>ocaml-ng.ocamlPackages_4_04</code> contains the OCaml compiler at version 4.04 and OCaml libraries compiled with that particular compiler.

)

~~A useful complement~~ to ~~merlin is [https:~~/~~/www~~.~~typerex~~.~~org/ocp-indent.html '''ocp-indent''']~~, ~~a customizable tool~~ to ~~indent OCaml~~ code~~. It can be installed using~~ <code>~~nix-env -iA nixpkgs.~~ocamlPackages.~~ocpIndent~~</code>~~. To enable it in Emacs, don’t forget to add the following line to your '''.emacs'''~~:

==== Custom version ====

So as to get the set of OCaml libraries built with/for a custom version of the OCaml compiler, e.g., to enable <code>flambda</code> support, you may use the <code>ocamlPackages.overrideScope</code> function:

~~(require 'ocp-indent~~)

ocamlPackagesFlambda = ocamlPackages.overrideScope (self: super: {

ocaml = super.ocaml.override { flambdaSupport = true; };

});

</syntaxHighlight>

~~== Specific version of the OCaml compiler ==~~

More details: https://github.com/NixOS/nixpkgs/pull/53357#issuecomment-451727433

Various versions of the '''ocamlPackage'' attribute set are available, corresponding to various versions of OCaml. For instance, the attribute set '''ocaml-ng.ocamlPackages_4_04''' contains the OCaml compiler at version 4.04 and OCaml libraries compiled with that particular compiler.

[[Category:Languages]]

@@ Line 1: / Line 1: @@
-Most packages related to OCaml, in particular the OCaml compiler and many libraries, belong to the '''ocamlPackages''' attribute set of nixpkgs.
+[[File:OCaml Logo.svg|alt=The OCaml logo: an orange background with a white foreground of a camel.|thumb|OCaml logo]]
-== Findlib, ocamlfind ==
+According to the official [ocaml.org Ocaml website]:<blockquote>
+ [Ocaml is]... an industrial-strength functional programming language with an emphasis on expressiveness and safety        </blockquote>
-OCaml libraries are usually located using [http://projects.camlcity.org/projects/findlib.html findlib] and the associated '''ocamlfind''' tool. These tools are found under the '''ocamlPackages.findlib''' attribute and rely on the '''OCAMLPATH''' environment variable.
+== Developping in OCaml with Nix ==
-A hook in the '''findlib''' package will automatically populate this variable with the paths to the other libraries. For instance, when starting a shell with
+Most packages related to OCaml, in particular the OCaml compiler and many libraries, belong to the <code>ocamlPackages</code> attribute set of nixpkgs. Tools for OCaml development are, in particular, available:
+* the [https://dune.build/ dune] builder;
+* the [https://github.com/ocaml/ocaml-lsp OCaml language server];
+* the [https://github.com/ocaml-ppx/ocamlformat ocamlformat formatter].
+=== Build tooling ===
+Modern development in OCaml tend to use <code>dune</code>, a build system dedicated for OCaml projects. Nixpkgs provide a dedicated helper [https://nixos.org/manual/nixpkgs/stable/#sec-language-ocaml-packaging buildDuneProject] to facilitate integration with <code>dune</code>.
+An example minimal flake for OCaml development is available below:
+{{Code|1=// flake.nix
+{
+  description = "Minimal flake for OCaml projects.";
+  inputs = {
+    flake-utils.url = "github:numtide/flake-utils";
+    nixpkgs.url = "nixpkgs";
+  };
+  outputs =
+    {
+      self,
+      flake-utils,
+      nixpkgs,
+      ...
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in
+      {
+        packages = {
+          default =
+          buildDunePackage {
+            pname = "My Ocaml Package";
+            duneVersion = "3";
+            version = "0.1";
+            minimalOCamlVersion = "4.14";
+            installTargets = "all doc";
+            src = ./.;
+            nativeBuildInputs = with p; [
+              dune_3
+            ];
+          };
+        };
+        devShells = {
+          default = pkgs.mkShell {
+            name = "Ocaml development shell environment.";
+            inputsFrom = [ self.packages.${system}.default ];
+            packages = with pkgs.ocaml-ng.ocamlPackages; [
+              ocamlformat
+              ocaml-lsp
+              utop
+              pkgs.gnumake
+            ];
+            shellHook = ''
+              echo "Welcome in the devshell."
+            '';
+          };
+        };
+      }
+    );
+}|lang=nix}}
+<code>nix develop</code> followed by <code>dune init project myproject</code> will drop you in a development shell.
+==== Opam ====
+OCaml has its own package manager, [https://opam.ocaml.org/ opam]. Trying to use it imperatively with Nix will result in errors. However, <code>opam</code> can generate a <code>.opam</code> file, which can be ingested by tools like [https://github.com/tweag/opam-nix opam-nix] to automatically generate a Nix derivation.
+==== Manual build with ocamlc, findlib, ocamlfind ====
+OCaml libraries are usually located using [http://projects.camlcity.org/projects/findlib.html findlib] and the associated <code>ocamlfind</code> tool. These tools are found under the <code>ocamlPackages.findlib</code> attribute and rely on the <code>OCAMLPATH</code> environment variable.
+A hook in the <code>findlib</code> package will automatically populate this variable with the paths to the other libraries. For instance, when starting a shell with
 <code>nix-shell --packages ocamlPackages.findlib ocamlPackages.batteries</code>
-will set the '''OCAMLPATH''' variable so that '''ocamlfind''' can locate the '''batteries''' library.
+will set the <code>OCAMLPATH</code> variable so that <code>ocamlfind</code> can locate the <code>batteries</code> library.
+This hook also sets the <code>CAML_LD_LIBRARY_PATH</code> environment variable that is used for locating the dynamically loaded shared libraries (aka stublibs).
-This hook also sets the '''CAML_LD_LIBRARY_PATH''' environment variable that is used for locating the dynamically loaded shared libraries (aka stublibs).
+=== Scripting with OCaml ===
+OCaml can be used in nix-shell scripts as follows:
+<syntaxHighlight lang=ocaml>
+#!/usr/bin/env nix-shell
+(*
+#!nix-shell --pure -i ocaml -p ocaml
+*)
-== Using Emacs ==
+print_string "Hello world! 🚀 \n";;
+</syntaxHighlight>
+=== Using Emacs ===
 [https://github.com/ocaml/tuareg Tuareg] is an Emacs OCaml mode. It can be installed with
 <code>nix-env -iA nixpkgs.emacsPackagesNg.tuareg</code>.
-Emacs must be configured to be able to find this package: you may need to add a line like this to your '''.emacs''' file, somewhere between <code>(require 'package)</code> and <code>(package-initialize)</code>:
+Emacs must be configured to be able to find this package: you may need to add a line like this to your <code>.emacs</code> file, somewhere between <code>(require 'package)</code> and <code>(package-initialize)</code>:
-  (add-to-list 'package-directory-list "~/.nix-profile/share/emacs/site-lisp/elpa")
+<syntaxHighlight lang=emacs>
+(add-to-list 'package-directory-list "~/.nix-profile/share/emacs/site-lisp/elpa")
+</syntaxHighlight>
 There is some more documentation in the [https://github.com/NixOS/nixpkgs/blob/master/pkgs/top-level/emacs-packages.nix nixpkgs sources].
@@ Line 26: / Line 112: @@
 Beware that merlin is specific to one particular version of OCaml (it won’t work correctly with a compiler of a different version).
-To configure Emacs and enable the merlin mode, add the following to your '''.emacs''':
+To configure Emacs and enable the merlin mode, add the following to your <code>.emacs</code>:
+<syntaxHighlight lang=emacs>
+(add-to-list 'load-path "~/.nix-profile/share/emacs/site-lisp")
+(require 'merlin)
+(add-hook 'tuareg-mode-hook 'merlin-mode t)
+</syntaxHighlight>
+Also, a specific variable (<code>merlin-command</code>) of the merlin mode must be overridden (its default is <code>opam</code>):
+<syntaxHighlight lang=emacs>
+(custom-set-variables
+  '(merlin-command "ocamlmerlin")
+)
+</syntaxHighlight>
-  (add-to-list 'load-path "~/.nix-profile/share/emacs/site-lisp")
+A useful complement to merlin is [https://www.typerex.org/ocp-indent.html '''ocp-indent'''], a customizable tool to indent OCaml code. It can be installed using <code>nix-env -iA nixpkgs.ocamlPackages.ocpIndent</code>. To enable it in Emacs, don’t forget to add the following line to your <code>.emacs</code>:
-  (require 'merlin)
-  (add-hook 'tuareg-mode-hook 'merlin-mode t)
-Also, a specific variable ('''merlin-command''') of the merlin mode must be overridden (its default is '''opam'''):
+<syntaxHighlight lang=emacs>
+(require 'ocp-indent)
+</syntaxHighlight>
-  (custom-set-variables
+=== Specific version of the OCaml compiler ===
-   '(merlin-command "ocamlmerlin")
+Various versions of the <code>ocamlPackage</code> attribute set are available, corresponding to various versions of OCaml. For instance, the attribute set <code>ocaml-ng.ocamlPackages_4_04</code> contains the OCaml compiler at version 4.04 and OCaml libraries compiled with that particular compiler.
-  )
-A useful complement to merlin is [https://www.typerex.org/ocp-indent.html '''ocp-indent'''], a customizable tool to indent OCaml code. It can be installed using <code>nix-env -iA nixpkgs.ocamlPackages.ocpIndent</code>. To enable it in Emacs, don’t forget to add the following line to your '''.emacs''':
+==== Custom version ====
+So as to get the set of OCaml libraries built with/for a custom version of the OCaml compiler, e.g., to enable <code>flambda</code> support, you may use the <code>ocamlPackages.overrideScope</code> function:
-   (require 'ocp-indent)
+<syntaxHighlight lang=nix>
+ocamlPackagesFlambda = ocamlPackages.overrideScope (self: super: {
+   ocaml = super.ocaml.override { flambdaSupport = true; };
+});
+</syntaxHighlight>
-== Specific version of the OCaml compiler ==
+More details: https://github.com/NixOS/nixpkgs/pull/53357#issuecomment-451727433
-Various versions of the '''ocamlPackage'' attribute set are available, corresponding to various versions of OCaml. For instance, the attribute set '''ocaml-ng.ocamlPackages_4_04''' contains the OCaml compiler at version 4.04 and OCaml libraries compiled with that particular compiler.
+[[Category:Languages]]