# Release 0.9 (2005-09-16)

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

    $ nix-store --clear-substitutes

first.

- Unpacking of patch sequences is much faster now since we no longer do redundant unpacking and repacking of intermediate paths.

- Nix now uses Berkeley DB 4.3.

- The `derivation` primitive is lazier. Attributes of dependent derivations can mutually refer to each other (as long as there are no data dependencies on the `outPath` and `drvPath` attributes computed by `derivation`).

  For example, the expression `derivation attrs` now evaluates to (essentially)

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

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

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

      webServer = derivation {
        ...
        hostName = "svn.cs.uu.nl";
        services = [svnService];
      };

      svnService = derivation {
        ...
        hostName = webServer.hostName;
      };

  Previously, this would yield a black hole (infinite recursion).

- `nix-build` now defaults to using `./default.nix` if no Nix expression is specified.

- `nix-instantiate`, when applied to a Nix expression that evaluates to a function, will call the function automatically if all its arguments have defaults.

- Nix now uses libtool to build dynamic libraries. This reduces the size of executables.

- A new list concatenation operator `++`. For example, `[1 2 3] ++ [4 5 6]` evaluates to `[1 2 3 4 5 6]`.

- 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 `r3578` and `r3580`.

- Various bug fixes and performance improvements.