add atexit (#4456)

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

diff --git a/docs/users_guide/using.xml b/docs/users_guide/using.xml
index 34f769a..05f1de4 100644 (file)
--- a/docs/users_guide/using.xml
+++ b/docs/users_guide/using.xml
@@ -1300,6 +1300,39 @@ f foo = foo { x = 6 }
       </varlistentry>
 
       <varlistentry>
+       <term>
+          <option>-fwarn-missing-import-lists</option>:
+         <indexterm><primary><option>-fwarn-import-lists</option></primary></indexterm>
+         <indexterm><primary>missing import lists, warning</primary></indexterm>
+         <indexterm><primary>import lists, missing</primary></indexterm>
+        </term>
+       <listitem>
+
+         <para>This flag warns if you use an unqualified 
+            <literal>import</literal> declaration
+           that does not explicitly list the entities brought into scope. For 
+           example
+      </para>
+<programlisting>
+module M where
+  import X( f )
+  import Y
+  import qualified Z
+  p x = f x x
+</programlisting>
+        <para>
+          The <option>-fwarn-import-lists</option> flag will warn about the import
+         of <literal>Y</literal> but not <literal>X</literal>
+         If module <literal>Y</literal> is later changed to export (say) <literal>f</literal>,
+          then the reference to <literal>f</literal> in <literal>M</literal> will become
+         ambiguous.  No warning is produced for the import of <literal>Z</literal>
+         because extending <literal>Z</literal>'s exports would be unlikely to produce
+         ambiguity in <literal>M</literal>.
+        </para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
        <term><option>-fwarn-missing-methods</option>:</term>
        <listitem>
          <indexterm><primary><option>-fwarn-missing-methods</option></primary></indexterm>
@@ -1668,7 +1701,7 @@ f "2"    = 2
       <para>We don't use a <option>-O*</option> flag for day-to-day
       work.  We use <option>-O</option> to get respectable speed;
       e.g., when we want to measure something.  When we want to go for
-      broke, we tend to use <option>-O2 -fvia-C</option> (and we go for
+      broke, we tend to use <option>-O2</option> (and we go for
       lots of coffee breaks).</para>
 
       <para>The easiest way to see what <option>-O</option> (etc.)