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nixos release notes: document incompatible changes due to Haskell NG

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Peter Simons 2015-06-01 15:19:53 +02:00
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nixos/doc/manual/release-notes/rl-unstable.xml
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@ -83,6 +83,64 @@ was accordingly renamed to <literal>bomi</literal>
</para> </para>
</listitem> </listitem>
<listitem>
<para>
Haskell packages can no longer be found by name, i.e. the commands
<literal>nix-env -qa cabal-install</literal> and <literal>nix-env -i
ghc</literal> will fail, even though we <emphasis>do</emphasis> ship
both <literal>cabal-install</literal> and <literal>ghc</literal>.
The reason for this inconvenience is the sheer size of the Haskell
package set: name-based lookups such as these would become much
slower than they are today if we'd add the entire Hackage database
into the top level attribute set. Instead, the list of Haskell
packages can be displayed by
</para>
<programlisting>
nix-env -f &quot;&lt;nixpkgs&gt;&quot; -qaP -A haskellPackages
</programlisting>
<para>
and packages can be installed with:
</para>
<programlisting>
nix-env -f &quot;&lt;nixpkgs&gt;&quot; -iA haskellPackages.cabal-install
</programlisting>
</listitem>
<listitem>
<para>
Previous versions of NixOS come with a feature called
<literal>ghc-wrapper</literal>, a small wrapper script that allows
GHC to transparently pick up on libraries installed in the user's
profile. This feature has been deprecated;
<literal>ghc-wrapper</literal> was removed from the distribution.
The proper way to register Haskell libraries with the compiler now
is the <literal>haskellPackages.ghcWithPackages</literal>
function.
<link xlink:href="https://nixos.org/wiki/Haskell">https://nixos.org/wiki/Haskell</link>
provides much information about this subject.
</para>
</listitem>
<listitem>
<para>
All Haskell builds that have been generated with version 1.x of
the <literal>cabal2nix</literal> utility are now invalid and need
to be re-generated with a current version of
<literal>cabal2nix</literal> to function. The most recent version
of this tool can be installed by running
<literal>nix-env -i cabal2nix</literal>.
</para>
</listitem>
<listitem>
<para>
The <literal>haskellPackages</literal> set in Nixpkgs used to have a
function attribute called <literal>extension</literal> that users
could override in their <literal>~/.nixpkgs/config.nix</literal>
files to configure additional attributes, etc. That function still
exists, but it's now called <literal>overrides</literal>.
</para>
</listitem>
</itemizedlist> </itemizedlist>
</para> </para>