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nixpkgs docs: document recursivelyUpdateUntil

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(cherry picked from commit c100a456b1)
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Graham Christensen 2018-10-12 16:51:05 -04:00
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108
doc/functions/library/attrsets.xml
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@ -1563,4 +1563,112 @@ lib.attrsets.zipAttrs
]]></programlisting>
</example>
</section>
<section xml:id="function-library-lib.attrsets.recursiveUpdateUntil">
<title><function>lib.attrsets.recursiveUpdateUntil</function></title>
<subtitle><literal>recursiveUpdateUntil :: ( [ String ] -> AttrSet -> AttrSet -> Bool ) -> AttrSet -> AttrSet -> AttrSet</literal>
</subtitle>
<xi:include href="./locations.xml" xpointer="lib.attrsets.recursiveUpdateUntil" />
<para>
Does the same as the update operator <literal>//</literal> except that
attributes are merged until the given predicate is verified. The predicate
should accept 3 arguments which are the path to reach the attribute, a part
of the first attribute set and a part of the second attribute set. When the
predicate is verified, the value of the first attribute set is replaced by
the value of the second attribute set.
</para>
<variablelist>
<varlistentry>
<term>
<varname>pred</varname>
</term>
<listitem>
<para>
<literal>[ String ] -> AttrSet -> AttrSet -> Bool</literal>
</para>
<variablelist>
<varlistentry>
<term>
<varname>path</varname>
</term>
<listitem>
<para>
The path to the values in the left and right hand sides.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>l</varname>
</term>
<listitem>
<para>
The left hand side value.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>r</varname>
</term>
<listitem>
<para>
The right hand side value.
</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>lhs</varname>
</term>
<listitem>
<para>
The left hand attribute set of the merge.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>rhs</varname>
</term>
<listitem>
<para>
The right hand attribute set of the merge.
</para>
</listitem>
</varlistentry>
</variablelist>
<example xml:id="function-library-lib.attrsets.recursiveUpdateUntil-example">
<title>Recursively merging two attribute sets</title>
<programlisting><![CDATA[
lib.attrsets.recursiveUpdateUntil (path: l: r: path == ["foo"])
{
# first attribute set
foo.bar = 1;
foo.baz = 2;
bar = 3;
}
{
#second attribute set
foo.bar = 1;
foo.quz = 2;
baz = 4;
}
=> {
foo.bar = 1; # 'foo.*' from the second set
foo.quz = 2; #
bar = 3; # 'bar' from the first set
baz = 4; # 'baz' from the second set
}
]]></programlisting>
</example>
</section>
</section>