nixpkgs/doc/languages-frameworks/ocaml.xml
2020-02-16 09:49:12 -08:00

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<section xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xml:id="sec-language-ocaml">
<title>OCaml</title>
<para>
OCaml libraries should be installed in <literal>$(out)/lib/ocaml/${ocaml.version}/site-lib/</literal>. Such directories are automatically added to the <literal>$OCAMLPATH</literal> environment variable when building another package that depends on them or when opening a <literal>nix-shell</literal>.
</para>
<para>
Given that most of the OCaml ecosystem is now built with dune, nixpkgs includes a convenience build support function called <literal>buildDunePackage</literal> that will build an OCaml package using dune, OCaml and findlib and any additional dependencies provided as <literal>buildInputs</literal> or <literal>propagatedBuildInputs</literal>.
</para>
<para>
Here is a simple package example. It defines an (optional) attribute <literal>minimumOCamlVersion</literal> that will be used to throw a descriptive evaluation error if building with an older OCaml is attempted. It uses the <literal>fetchFromGitHub</literal> fetcher to get its source. It sets the <literal>doCheck</literal> (optional) attribute to <literal>true</literal> which means that tests will be run with <literal>dune runtest -p angstrom</literal> after the build (<literal>dune build -p angstrom</literal>) is complete. It uses <literal>alcotest</literal> as a build input (because it is needed to run the tests) and <literal>bigstringaf</literal> and <literal>result</literal> as propagated build inputs (thus they will also be available to libraries depending on this library). The library will be installed using the <literal>angstrom.install</literal> file that dune generates.
</para>
<programlisting>
{ stdenv, fetchFromGitHub, buildDunePackage, alcotest, result, bigstringaf }:
buildDunePackage rec {
pname = "angstrom";
version = "0.10.0";
minimumOCamlVersion = "4.03";
src = fetchFromGitHub {
owner = "inhabitedtype";
repo = pname;
rev = version;
sha256 = "0lh6024yf9ds0nh9i93r9m6p5psi8nvrqxl5x7jwl13zb0r9xfpw";
};
buildInputs = [ alcotest ];
propagatedBuildInputs = [ bigstringaf result ];
doCheck = true;
meta = {
homepage = "https://github.com/inhabitedtype/angstrom";
description = "OCaml parser combinators built for speed and memory efficiency";
license = stdenv.lib.licenses.bsd3;
maintainers = with stdenv.lib.maintainers; [ sternenseemann ];
};
}
</programlisting>
<para>
Here is a second example, this time using a source archive generated with <literal>dune-release</literal>. It is a good idea to use this archive when it is available as it will usually contain substituted variables such as a <literal>%%VERSION%%</literal> field. This library does not depend on any other OCaml library and no tests are run after building it.
</para>
<programlisting>
{ stdenv, fetchurl, buildDunePackage }:
buildDunePackage rec {
pname = "wtf8";
version = "1.0.1";
minimumOCamlVersion = "4.01";
src = fetchurl {
url = "https://github.com/flowtype/ocaml-${pname}/releases/download/v${version}/${pname}-${version}.tbz";
sha256 = "1msg3vycd3k8qqj61sc23qks541cxpb97vrnrvrhjnqxsqnh6ygq";
};
meta = with stdenv.lib; {
homepage = "https://github.com/flowtype/ocaml-wtf8";
description = "WTF-8 is a superset of UTF-8 that allows unpaired surrogates.";
license = licenses.mit;
maintainers = [ maintainers.eqyiel ];
};
}
</programlisting>
</section>