Adding docs for bundlerApp.

<para>Please check in the <filename>Gemfile</filename>, <filename>Gemfile.lock</filename> and the <filename>gemset.nix</filename> so future updates can be run easily.

</para>

<para>Resulting derivations also have two helpful items, <literal>env</literal> and <literal>wrapper</literal>. The first one allows one to quickly drop into

<para>For tools written in Ruby - i.e. where the desire is to install a package and then execute e.g. <command>rake</command> at the command line, there is an alternative builder called <literal>bundlerApp</literal>. Set up the <filename>gemset.nix</filename> the same way, and then, for example:

</para>

<screen>

  <![CDATA[{ lib, bundlerApp }:

bundlerApp {

  pname = "corundum";

  gemdir = ./.;

  exes = [ "corundum-skel" ];

  meta = with lib; {

    description = "Tool and libraries for maintaining Ruby gems.";

    homepage    = https://github.com/nyarly/corundum;

    license     = licenses.mit;

    maintainers = [ maintainers.nyarly ];

    platforms   = platforms.unix;

  };

}]]>

<para>The chief advantage of <literal>bundlerApp</literal> over <literal>bundlerEnv</literal> is the the executables introduced in the environment are precisely those selected in the <literal>exes</literal> list, as opposed to <literal>bundlerEnv</literal> which adds all the executables made available by gems in the gemset, which can mean e.g. <command>rspec</command> or <command>rake</command> in unpredicable versions available from various packages.

<para>Resulting derivations for both builders also have two helpful items, <literal>env</literal> and <literal>wrapper</literal>. The first one allows one to quickly drop into

<command>nix-shell</command> with the specified environment present. E.g. <command>nix-shell -A sensu.env</command> would give you an environment with Ruby preset

so it has all the libraries necessary for <literal>sensu</literal> in its paths. The second one can be used to make derivations from custom Ruby scripts which have

<filename>Gemfile</filename>s with their dependencies specified. It is a derivation with <command>ruby</command> wrapped so it can find all the needed dependencies.

For example, to make a derivation <literal>my-script</literal> for a <filename>my-script.rb</filename> (which should be placed in <filename>bin</filename>) you should

run <command>bundix</command> as specified above and then use <literal>bundlerEnv</literal> lile this:</para>

run <command>bundix</command> as specified above and then use <literal>bundlerEnv</literal> like this:</para>

<programlisting>

<![CDATA[let env = bundlerEnv {

</programlisting>

</section>

  meta = with lib; {

    description = "Tool and libraries for maintaining Ruby gems.";

    homepage    = http://sass-lang.com/;

    homepage    = https://github.com/nyarly/corundum;

    license     = licenses.mit;

    maintainers = [ maintainers.nyarly ];

    platforms   = platforms.unix;