<section xmlns="http://docbook.org/ns/docbook"
      xmlns:xlink="http://www.w3.org/1999/xlink"
      xmlns:xi="http://www.w3.org/2001/XInclude"
      version="5.0"
      xml:id="ch-relnotes-0.9">

<title>Release 0.9 (2005-09-16)</title>

<para>NOTE: this version of Nix uses Berkeley DB 4.3 instead of 4.2.
The database is upgraded automatically, but you should be careful not
to use old versions of Nix that still use Berkeley DB 4.2.  In
particular, if you use a Nix installed through Nix, you should run

<screen>
$ nix-store --clear-substitutes</screen>

first.</para>


<itemizedlist>

  <listitem><para>Unpacking of patch sequences is much faster now
  since we no longer do redundant unpacking and repacking of
  intermediate paths.</para></listitem>

  <listitem><para>Nix now uses Berkeley DB 4.3.</para></listitem>

  <listitem><para>The <function>derivation</function> primitive is
  lazier.  Attributes of dependent derivations can mutually refer to
  each other (as long as there are no data dependencies on the
  <varname>outPath</varname> and <varname>drvPath</varname> attributes
  computed by <function>derivation</function>).</para>

  <para>For example, the expression <literal>derivation
  attrs</literal> now evaluates to (essentially)

  <programlisting>
attrs // {
  type = "derivation";
  outPath = derivation! attrs;
  drvPath = derivation! attrs;
}</programlisting>

  where <function>derivation!</function> is a primop that does the
  actual derivation instantiation (i.e., it does what
  <function>derivation</function> used to do).  The advantage is that
  it allows commands such as <command>nix-env -qa</command> and
  <command>nix-env -i</command> to be much faster since they no longer
  need to instantiate all derivations, just the
  <varname>name</varname> attribute.</para>

  <para>Also, it allows derivations to cyclically reference each
  other, for example,

  <programlisting>
webServer = derivation {
  ...
  hostName = "svn.cs.uu.nl";
  services = [svnService];
};
&#x20;
svnService = derivation {
  ...
  hostName = webServer.hostName;
};</programlisting>

  Previously, this would yield a black hole (infinite recursion).</para>

  </listitem>

  <listitem><para><command>nix-build</command> now defaults to using
  <filename>./default.nix</filename> if no Nix expression is
  specified.</para></listitem>

  <listitem><para><command>nix-instantiate</command>, when applied to
  a Nix expression that evaluates to a function, will call the
  function automatically if all its arguments have
  defaults.</para></listitem>

  <listitem><para>Nix now uses libtool to build dynamic libraries.
  This reduces the size of executables.</para></listitem>

  <listitem><para>A new list concatenation operator
  <literal>++</literal>.  For example, <literal>[1 2 3] ++ [4 5
  6]</literal> evaluates to <literal>[1 2 3 4 5
  6]</literal>.</para></listitem>

  <listitem><para>Some currently undocumented primops to support
  low-level build management using Nix (i.e., using Nix as a Make
  replacement).  See the commit messages for <literal>r3578</literal>
  and <literal>r3580</literal>.</para></listitem>

  <listitem><para>Various bug fixes and performance
  improvements.</para></listitem>

</itemizedlist>

</section>
