Commit 72f5cd2f authored by simonpj's avatar simonpj
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[project @ 2003-07-24 07:45:09 by simonpj]

Document deriving(Typeable,Data)
parent 57d3c7c8
......@@ -2980,6 +2980,25 @@ Result type signatures are not yet implemented in Hugs.
</sect2>
<sect2 id="deriving-typeable">
<title>Deriving clause for classes <literal>Typeable</literal> and <literal>Data</literal></title>
<para>
Haskell 98 allows the programmer to add "<literal>deriving( Eq, Ord )</literal>" to a data type
declaration, to generate a standard instance declaration for classes specified in the <literal>deriving</literal> clause.
In Haskell 98, the only classes that may appear in the <literal>deriving</literal> clause are the standard
classes <literal>Eq</literal>, <literal>Ord</literal>,
<literal>Enum</literal>, <literal>Ix</literal>, <literal>Bounded</literal>, <literal>Read</literal>, and <literal>Show</literal>.
</para>
<para>
GHC extends this list with two more classes that may be automatically derived
(provided the <option>-fglasgow-exts</option> flag is specified):
<literal>Typeable</literal>, and <literal>Data</literal>. These classes are defined in the library
modules <literal>Data.Dynamic</literal> and <literal>Data.Generics</literal> respectively, and the
appropriate class must be in scope before it can be mentioned in the <literal>deriving</literal> clause.
</para>
</sect2>
<sect2 id="newtype-deriving">
<title>Generalised derived instances for newtypes</title>
......
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