From 9ae39b3553146b3ae72fc5ac26654e1930baba3d Mon Sep 17 00:00:00 2001
From: Graham Christensen <graham@grahamc.com>
Date: Tue, 2 Oct 2018 14:03:59 -0400
Subject: nixpkgs docs: move generators to its own file

---
 doc/functions/generators.xml | 90 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 doc/functions/generators.xml

(limited to 'doc/functions')

diff --git a/doc/functions/generators.xml b/doc/functions/generators.xml
new file mode 100644
index 000000000000..0a9c346145f9
--- /dev/null
+++ b/doc/functions/generators.xml
@@ -0,0 +1,90 @@
+<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>
-- 
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