- The VirtualBox host and guest options have been named more consistently. They can now found in `virtualisation.virtualbox.host.*` instead of `services.virtualboxHost.*` and `virtualisation.virtualbox.guest.*` instead of `services.virtualboxGuest.*`.

  Also, there now is support for the `vboxsf` file system using the `fileSystems` configuration attribute. An example of how this can be used in a configuration:

```nix
{
  fileSystems."/shiny" = {
    device = "myshinysharedfolder";
    fsType = "vboxsf";
  };
}
```

- "`nix-env -qa`" no longer discovers Haskell packages by name. The only packages visible in the global scope are `ghc`, `cabal-install`, and `stack`, but all other packages are hidden. The reason for this inconvenience is the sheer size of the Haskell package set. Name-based lookups are expensive, and most `nix-env -qa` operations would become much slower if we'd add the entire Hackage database into the top level attribute set. Instead, the list of Haskell packages can be displayed by running:

```ShellSession
nix-env -f "<nixpkgs>" -qaP -A haskellPackages
```

Executable programs written in Haskell can be installed with:

```ShellSession
nix-env -f "<nixpkgs>" -iA haskellPackages.pandoc
```

Installing Haskell _libraries_ this way, however, is no longer supported. See the next item for more details.

- Previous versions of NixOS came with a feature called `ghc-wrapper`, a small script that allowed GHC to transparently pick up on libraries installed in the user's profile. This feature has been deprecated; `ghc-wrapper` was removed from the distribution. The proper way to register Haskell libraries with the compiler now is the `haskellPackages.ghcWithPackages` function. The [User's Guide to the Haskell Infrastructure](https://nixos.org/nixpkgs/manual/#users-guide-to-the-haskell-infrastructure) provides more information about this subject.

- All Haskell builds that have been generated with version 1.x of the `cabal2nix` utility are now invalid and need to be re-generated with a current version of `cabal2nix` to function. The most recent version of this tool can be installed by running `nix-env -i cabal2nix`.

- The `haskellPackages` set in Nixpkgs used to have a function attribute called `extension` that users could override in their `~/.nixpkgs/config.nix` files to configure additional attributes, etc. That function still exists, but it's now called `overrides`.

- The OpenBLAS library has been updated to version `0.2.14`. Support for the `x86_64-darwin` platform was added. Dynamic architecture detection was enabled; OpenBLAS now selects microarchitecture-optimized routines at runtime, so optimal performance is achieved without the need to rebuild OpenBLAS locally. OpenBLAS has replaced ATLAS in most packages which use an optimized BLAS or LAPACK implementation.

- The `phpfpm` is now using the default PHP version (`pkgs.php`) instead of PHP 5.4 (`pkgs.php54`).

- The `locate` service no longer indexes the Nix store by default, preventing packages with potentially numerous versions from cluttering the output. Indexing the store can be activated by setting `services.locate.includeStore = true`.