[project @ 2003-12-16 16:17:49 by simonpj]

Clarify warn-unused-bindings documention

diff --git a/ghc/docs/users_guide/using.sgml b/ghc/docs/users_guide/using.sgml
index fb5f6f6..2c8e1ca 100644 (file)
--- a/ghc/docs/users_guide/using.sgml
+++ b/ghc/docs/users_guide/using.sgml
@@ -940,6 +940,13 @@ f "2"    = 2
          <para>Report any function definitions (and local bindings)
           which are unused.  For top-level functions, the warning is
           only given if the binding is not exported.</para>
+         <para>A definition is regarded as "used" if (a) it is exported, or (b) it is
+           mentioned in the right hand side of another definition that is used, or (c) the 
+           function it defines begins with an underscore.  The last case provides a 
+           way to suppress unused-binding warnings selectively.  </para>
+         <para> Notice that a variable
+           is reported as unused even if it appears in the right-hand side of another
+           unused binding. </para>
        </listitem>
       </varlistentry>
 
@@ -950,8 +957,10 @@ f "2"    = 2
          <indexterm><primary>unused imports, warning</primary></indexterm>
          <indexterm><primary>imports, unused</primary></indexterm>
 
-         <para>Report any objects that are explicitly imported but
-         never used.</para>
+         <para>Report any modules that are explicitly imported but
+         never used.  However, the form <literal>import M()</literal> is
+         never reported as an unused import, because it is a useful idiom
+         for importing instance declarations, which are anonymous in Haskell.</para>
        </listitem>
       </varlistentry>