Improve documentation of MagicHash and primitive types generally (Trac #2547)

[ghc-hetmet.git] / docs / users_guide / separate_compilation.xml

diff --git a/docs/users_guide/separate_compilation.xml b/docs/users_guide/separate_compilation.xml
index 1bdb0c5..01748ae 100644 (file)
--- a/docs/users_guide/separate_compilation.xml
+++ b/docs/users_guide/separate_compilation.xml
@@ -1169,7 +1169,8 @@ just in case they contain an instance declaration that matters to M.  This would
 be a disaster in practice, so GHC tries to be clever. </para>
 
 <para>In particular, if an instance declaration is in the same module as the definition
-of any type or class mentioned in the head of the instance declaration, then
+of any type or class mentioned in the <emphasis>head</emphasis> of the instance declaration 
+(the part after the &ldquo;<literal>=&gt;</literal>&rdquo;; see <xref linkend="instance-rules"/>), then
 GHC has to visit that interface file anyway.  Example:</para>
 <programlisting>
   module A where
@@ -1208,7 +1209,7 @@ functional dependency:
     class E x y | y -> x where ...
 </programlisting>
 Then in some importing module M, the constraint <literal>(E a Int)</literal> should be "improved" by setting
-<literal>a = Int</literal>, <emphasis>even though there is no explicit mention
+<literal>a = T</literal>, <emphasis>even though there is no explicit mention
 of <literal>T</literal> in M</emphasis>.</para>
 
 These considerations lead to the following definition of an orphan module:
@@ -1232,7 +1233,7 @@ These considerations lead to the following definition of an orphan module:
        </para></listitem>
   </itemizedlist>
   </para>
-  <para> Only the instance head  (the part after the &ldquo;<literal>=&gt;</literal>&rdquo;)
+  <para> Only the instance head 
   counts.  In the example above, it is not good enough for C's declaration
   to be in module A; it must be the declaration of D or T.</para>
   </listitem>
@@ -1246,7 +1247,13 @@ These considerations lead to the following definition of an orphan module:
 
 
 
-<para>GHC will warn you if you are creating an orphan module, if you add `-fwarn-orphan-modules`.
+<para>If you use the flag <option>-fwarn-orphans</option>, GHC will warn you 
+if you are creating an orphan module.
+Like any warning, you can switch the warning off with <option>-fno-warn-orphans</option>, 
+and <option>-Werror</option>
+will make the compilation fail if the warning is issued.
+</para>
+<para>
 You can identify an orphan module by looking in its interface
 file, <filename>M.hi</filename>, using the
 <link linkend="modes"><option>--show-iface</option> mode</link>.  If there is a <literal>[orphan module]</literal> on the