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<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xml:id="chap-conventions">
<title>Coding conventions</title>
<section><title>Syntax</title>
<itemizedlist>
<listitem><para>Use 2 spaces of indentation per indentation level in
Nix expressions, 4 spaces in shell scripts.</para></listitem>
<listitem><para>Do not use tab characters, i.e. configure your
editor to use soft tabs. For instance, use <literal>(setq-default
indent-tabs-mode nil)</literal> in Emacs. Everybody has different
tab settings so it’s asking for trouble.</para></listitem>
<listitem><para>Use <literal>lowerCamelCase</literal> for variable
names, not <literal>UpperCamelCase</literal>. TODO: naming of
attributes in
<filename>all-packages.nix</filename>?</para></listitem>
<listitem><para>Function calls with attribute set arguments are
written as
<programlisting>
foo {
arg = ...;
}
</programlisting>
not
<programlisting>
foo
{
arg = ...;
}
</programlisting>
Also fine is
<programlisting>
foo { arg = ...; }
</programlisting>
if it's a short call.</para></listitem>
<listitem><para>In attribute sets or lists that span multiple lines,
the attribute names or list elements should be aligned:
<programlisting>
# A long list.
list =
[ elem1
elem2
elem3
];
# A long attribute set.
attrs =
{ attr1 = short_expr;
attr2 =
if true then big_expr else big_expr;
};
# Alternatively:
attrs = {
attr1 = short_expr;
attr2 =
if true then big_expr else big_expr;
};
</programlisting>
</para></listitem>
<listitem><para>Short lists or attribute sets can be written on one
line:
<programlisting>
# A short list.
list = [ elem1 elem2 elem3 ];
# A short set.
attrs = { x = 1280; y = 1024; };
</programlisting>
</para></listitem>
<listitem><para>Breaking in the middle of a function argument can
give hard-to-read code, like
<programlisting>
someFunction { x = 1280;
y = 1024; } otherArg
yetAnotherArg
</programlisting>
(especially if the argument is very large, spanning multiple
lines).</para>
<para>Better:
<programlisting>
someFunction
{ x = 1280; y = 1024; }
otherArg
yetAnotherArg
</programlisting>
or
<programlisting>
let res = { x = 1280; y = 1024; };
in someFunction res otherArg yetAnotherArg
</programlisting>
</para></listitem>
<listitem><para>The bodies of functions, asserts, and withs are not
indented to prevent a lot of superfluous indentation levels, i.e.
<programlisting>
{ arg1, arg2 }:
assert system == "i686-linux";
stdenv.mkDerivation { ...
</programlisting>
not
<programlisting>
{ arg1, arg2 }:
assert system == "i686-linux";
stdenv.mkDerivation { ...
</programlisting>
</para></listitem>
<listitem><para>Function formal arguments are written as:
<programlisting>
{ arg1, arg2, arg3 }:
</programlisting>
but if they don't fit on one line they're written as:
<programlisting>
{ arg1, arg2, arg3
, arg4, ...
, # Some comment...
argN
}:
</programlisting>
</para></listitem>
</itemizedlist>
</section>
<section><title>File naming and organisation</title>
<para>Names of files and directories should be in lowercase, with
dashes between words — not in camel case. For instance, it should be
<filename>all-packages.nix</filename>, not
<filename>allPackages.nix</filename> or
<filename>AllPackages.nix</filename>.</para>
</section>
</chapter>
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