<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>