<indexterm><primary>packages</primary>
<secondary>using</secondary></indexterm>
- <para>Some packages are automatically available: you don't need
+ <para>Some packages, called <emphasis>auto packages</emphasis>,
+ are automatically available: you don't need
to specify any extra flags to use them (except in certain
circumstances; see below). All the packages which contain
hierarchical libraries fall into this category.</para>
be imported in your Haskell source, however). It also
causes the relevant libraries to be linked when linking is
being done.</para>
+ <para>Some packages depend on other packages, for example the
+ <literal>text</literal> package makes use of some of the modules
+ in the <literal>lang</literal> package. The package system
+ takes care of all these dependencies, so that when you say
+ <literal>-package text</literal> on the command line, you
+ automatically get <literal>-package lang</literal> too.</para>
</listitem>
</varlistentry>
</variablelist>
<para>There's one case where you need to use the
<option>-package</option> option even for auto packages: when
- linking a program in batch mode<footnote><para>This is because
+ linking a program in batch mode mode (<xref linkend="options-order">)
+ <footnote><para>This is because
GHC can't figure out from the object files which packages are
required; in <option>––make</option> mode and in
GHCi the compiler has more information available to figure out
in the future.</para></footnote>. For example, to link a
program consisting of objects <filename>Foo.o</filename> and
<filename>Main.o</filename>, where we made use of the
- <literal>network</literal> package:</para>
+ <literal>network</literal> package, we need to give GHC the <literal>-package</literal> flag thus:
<screen>$ ghc -o myprog Foo.o Main.o -package network</screen>
- <para>Some packages depend on other packages, for example the
- <literal>text</literal> package makes use of some of the modules
- in the <literal>lang</literal> package. The package system
- takes care of all these dependencies, so that when you say
- <literal>-package text</literal> on the command line, you
- automatically get <literal>-package lang</literal> too.</para>
+ The same flag is necessary even if we compiled the modules from source, because GHC still
+ reckons it's in batch mode:
+<screen>$ ghc -o myprog Foo.hs Main.hs -package network</screen>
+In <literal>--make</literal> and <literal>--interactive</literal> modes (<xref linkend="modes">), however, GHC figures out
+the auto packages required for linking without further assistance.
+</para>
+
</sect2>
+
<sect2 id="using-local-packages">
<title>Maintaining a local set of packages</title>