mirror of
https://github.com/NixOS/nixpkgs.git
synced 2024-12-13 16:15:30 +00:00
90 lines
2.6 KiB
XML
90 lines
2.6 KiB
XML
<section xmlns="http://docbook.org/ns/docbook"
|
||
xmlns:xlink="http://www.w3.org/1999/xlink"
|
||
xmlns:xi="http://www.w3.org/2001/XInclude"
|
||
xml:id="sec-generators">
|
||
<title>Generators</title>
|
||
|
||
<para>
|
||
Generators are functions that create file formats from nix data structures,
|
||
e. g. for configuration files. There are generators available for:
|
||
<literal>INI</literal>, <literal>JSON</literal> and <literal>YAML</literal>
|
||
</para>
|
||
|
||
<para>
|
||
All generators follow a similar call interface: <code>generatorName
|
||
configFunctions data</code>, where <literal>configFunctions</literal> is an
|
||
attrset of user-defined functions that format nested parts of the content.
|
||
They each have common defaults, so often they do not need to be set manually.
|
||
An example is <code>mkSectionName ? (name: libStr.escape [ "[" "]" ]
|
||
name)</code> from the <literal>INI</literal> generator. It receives the name
|
||
of a section and sanitizes it. The default <literal>mkSectionName</literal>
|
||
escapes <literal>[</literal> and <literal>]</literal> with a backslash.
|
||
</para>
|
||
|
||
<para>
|
||
Generators can be fine-tuned to produce exactly the file format required by
|
||
your application/service. One example is an INI-file format which uses
|
||
<literal>: </literal> as separator, the strings
|
||
<literal>"yes"</literal>/<literal>"no"</literal> as boolean values and
|
||
requires all string values to be quoted:
|
||
</para>
|
||
|
||
<programlisting>
|
||
with lib;
|
||
let
|
||
customToINI = generators.toINI {
|
||
# specifies how to format a key/value pair
|
||
mkKeyValue = generators.mkKeyValueDefault {
|
||
# specifies the generated string for a subset of nix values
|
||
mkValueString = v:
|
||
if v == true then ''"yes"''
|
||
else if v == false then ''"no"''
|
||
else if isString v then ''"${v}"''
|
||
# and delegats all other values to the default generator
|
||
else generators.mkValueStringDefault {} v;
|
||
} ":";
|
||
};
|
||
|
||
# the INI file can now be given as plain old nix values
|
||
in customToINI {
|
||
main = {
|
||
pushinfo = true;
|
||
autopush = false;
|
||
host = "localhost";
|
||
port = 42;
|
||
};
|
||
mergetool = {
|
||
merge = "diff3";
|
||
};
|
||
}
|
||
</programlisting>
|
||
|
||
<para>
|
||
This will produce the following INI file as nix string:
|
||
</para>
|
||
|
||
<programlisting>
|
||
[main]
|
||
autopush:"no"
|
||
host:"localhost"
|
||
port:42
|
||
pushinfo:"yes"
|
||
str\:ange:"very::strange"
|
||
|
||
[mergetool]
|
||
merge:"diff3"
|
||
</programlisting>
|
||
|
||
<note>
|
||
<para>
|
||
Nix store paths can be converted to strings by enclosing a derivation
|
||
attribute like so: <code>"${drv}"</code>.
|
||
</para>
|
||
</note>
|
||
|
||
<para>
|
||
Detailed documentation for each generator can be found in
|
||
<literal>lib/generators.nix</literal>.
|
||
</para>
|
||
</section>
|