blob: 0a9c346145f9952c7b707f88e23c08677b14a4ab (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
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>
|