[commit: ghc] ghc-7.4: Document the Num superclass divergence from H98/H2010 (0877e14)

[Ian Lynagh]

Repository : ssh://darcs.haskell.org//srv/darcs/ghc

On branch  : ghc-7.4

http://hackage.haskell.org/trac/ghc/changeset/0877e14e3b4accd706c80b5087f1b8e5a08bec59

>---------------------------------------------------------------

commit 0877e14e3b4accd706c80b5087f1b8e5a08bec59
Author: Ian Lynagh <igloo at earth.li>
Date:   Sat Jan 14 13:40:58 2012 +0000

    Document the Num superclass divergence from H98/H2010

>---------------------------------------------------------------

 docs/users_guide/bugs.xml |   33 +++++++++++++++++++++++++++++++++
 1 files changed, 33 insertions(+), 0 deletions(-)

diff --git a/docs/users_guide/bugs.xml b/docs/users_guide/bugs.xml
index 12ef946..9da7927 100644
--- a/docs/users_guide/bugs.xml
+++ b/docs/users_guide/bugs.xml
@@ -150,6 +150,39 @@ main = do args &lt;- getArgs
 
       <variablelist>
 	<varlistentry>
+	  <term>Num superclasses</term>
+	  <listitem>
+	    <para>
+              The <literal>Num</literal> class does not have
+              <literal>Show</literal> or <literal>Eq</literal>
+              superclasses.
+            </para>
+
+	    <para>
+              You can make code that works with both
+              Haskell98/Haskell2010 and GHC by:
+              <itemizedlist>
+                <listitem>
+                  <para>
+                    Whenever you make a <literal>Num</literal> instance
+                    of a type, also make <literal>Show</literal> and
+                    <literal>Eq</literal> instances, and
+                  </para>
+                </listitem>
+                <listitem>
+                  <para>
+                    Whenever you give a function, instance or class a
+                    <literal>Num t</literal> constraint, also give it
+                    <literal>Show t</literal> and
+                    <literal>Eq t</literal> constraints.
+                  </para>
+                </listitem>
+              </itemizedlist>
+            </para>
+	    </listitem>
+	  </varlistentry>
+
+	<varlistentry>
 	  <term>Multiply-defined array elements&mdash;not checked:</term>
 	  <listitem>
 	    <para>This code fragment should