From: simonpj <unknown>
Date: Tue, 8 Mar 2005 08:48:35 +0000 (+0000)
Subject: [project @ 2005-03-08 08:48:35 by simonpj]
X-Git-Tag: Initial_conversion_from_CVS_complete~957
X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=commitdiff_plain;h=c2c84b7142562656fdb86d18a6e84e0a5d31546c;hp=f97dcf9fc2ea2a419087bca53f2fea811c5181a9

[project @ 2005-03-08 08:48:35 by simonpj]
Add notes about newtype deriving
---

diff --git a/ghc/docs/users_guide/glasgow_exts.xml b/ghc/docs/users_guide/glasgow_exts.xml
index a25d42e..efd7a13 100644
--- a/ghc/docs/users_guide/glasgow_exts.xml
+++ b/ghc/docs/users_guide/glasgow_exts.xml
@@ -3226,7 +3226,7 @@ class to the new type:
 <para>
 
 As a result of this extension, all derived instances in newtype
-declarations are treated uniformly (and implemented just by reusing
+ declarations are treated uniformly (and implemented just by reusing
 the dictionary for the representation type), <emphasis>except</emphasis>
 <literal>Show</literal> and <literal>Read</literal>, which really behave differently for
 the newtype and its representation.
@@ -3307,6 +3307,14 @@ then we would not have been able to derive an instance for the
 classes usually have one "main" parameter for which deriving new
 instances is most interesting.
 </para>
+<para>Lastly, all of this applies only for classes other than
+<literal>Read</literal>, <literal>Show</literal>, <literal>Typeable</literal>, 
+and <literal>Data</literal>, for which the built-in derivation applies (section
+4.3.3. of the Haskell Report).
+(For the standard classes <literal>Eq</literal>, <literal>Ord</literal>,
+<literal>Ix</literal>, and <literal>Bounded</literal> it is immaterial whether
+the standard method is used or the one described here.)
+</para>
 </sect3>
 
 </sect2>