From 0877e14e3b4accd706c80b5087f1b8e5a08bec59 Mon Sep 17 00:00:00 2001
From: Ian Lynagh <igloo@earth.li>
Date: Sat, 14 Jan 2012 13:40:58 +0000
Subject: [PATCH] Document the Num superclass divergence from H98/H2010
---
docs/users_guide/bugs.xml | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)
diff --git a/docs/users_guide/bugs.xml b/docs/users_guide/bugs.xml
index 12ef9460da3f..9da7927bc9f3 100644
--- a/docs/users_guide/bugs.xml
+++ b/docs/users_guide/bugs.xml
@@ -149,6 +149,39 @@ main = do args <- getArgs
<title>Numbers, basic types, and built-in classes</title>
<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—not checked:</term>
<listitem>
--
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