forked from mirrors/nixpkgs
75 lines
2.6 KiB
XML
75 lines
2.6 KiB
XML
<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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xml:id="sec-generators">
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<title>Generators</title>
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<para>
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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>
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</para>
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<para>
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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.
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</para>
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<para>
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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:
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</para>
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<programlisting>
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with lib;
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let
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customToINI = generators.toINI {
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# specifies how to format a key/value pair
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mkKeyValue = generators.mkKeyValueDefault {
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# specifies the generated string for a subset of nix values
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mkValueString = v:
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if v == true then ''"yes"''
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else if v == false then ''"no"''
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else if isString v then ''"${v}"''
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# and delegats all other values to the default generator
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else generators.mkValueStringDefault {} v;
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} ":";
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};
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# the INI file can now be given as plain old nix values
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in customToINI {
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main = {
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pushinfo = true;
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autopush = false;
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host = "localhost";
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port = 42;
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};
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mergetool = {
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merge = "diff3";
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};
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}
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</programlisting>
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<para>
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This will produce the following INI file as nix string:
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</para>
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<programlisting>
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[main]
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autopush:"no"
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host:"localhost"
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port:42
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pushinfo:"yes"
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str\:ange:"very::strange"
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[mergetool]
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merge:"diff3"
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</programlisting>
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<note>
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<para>
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Nix store paths can be converted to strings by enclosing a derivation attribute like so: <code>"${drv}"</code>.
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</para>
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</note>
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<para>
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Detailed documentation for each generator can be found in <literal>lib/generators.nix</literal>.
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</para>
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</section>
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