Implement poly-kinded Typeable

This patch makes the Data.Typeable.Typeable class work with arguments of any
kind. In particular, this removes the Typeable1..7 class hierarchy, greatly
simplyfing the whole Typeable story. Also added is the AutoDeriveTypeable
language extension, which will automatically derive Typeable for all types and
classes declared in that module. Since there is now no good reason to give
handwritten instances of the Typeable class, those are ignored (for backwards
compatibility), and a warning is emitted.

The old, kind-* Typeable class is now called OldTypeable, and lives in the
Data.OldTypeable module. It is deprecated, and should be removed in some future
version of GHC.

3 files changed, 43 insertions, 15 deletions

diff --git a/docs/users_guide/flags.xml b/docs/users_guide/flags.xml
index 5e2e52d38d..bc583acabc 100644
--- a/docs/users_guide/flags.xml
+++ b/docs/users_guide/flags.xml
@@ -1061,6 +1061,12 @@
             <entry><option>-XNoDeriveDataTypeable</option></entry>
           </row>
           <row>
+            <entry><option>-XAutoDeriveTypeable</option></entry>
+            <entry>Automatically derive Typeable instances for every datatype and type class declaration.</entry>
+            <entry>dynamic</entry>
+            <entry><option>-XNoAutoDeriveTypeable</option></entry>
+          </row>
+          <row>
             <entry><option>-XDeriveGeneric</option></entry>
             <entry>Enable <link linkend="deriving-typeable">deriving for the Generic class</link>.</entry>
             <entry>dynamic</entry>
@@ -1447,6 +1453,14 @@
             <entry><option>-fno-warn-warnings-deprecations</option></entry>
           </row>
 
+          <row>
+            <entry><option>-fwarn-typeable-instances</option></entry>
+            <entry>warn if there are any handwritten <literal>Typeable</literal>
+                   instances (see <xref linkend="deriving-typeable"/>)</entry>
+            <entry>dynamic</entry>
+            <entry><option>-fno-warn-typeable-instances</option></entry>
+          </row>
+
         </tbody>
       </tgroup>
     </informaltable>
diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index e1d21c3506..2a0917c039 100644
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -3379,19 +3379,19 @@ GHC extends this list with several more classes that may be automatically derive
 <literal>Typeable</literal>, and <literal>Data</literal>, defined in the library
 modules <literal>Data.Typeable</literal> and <literal>Data.Generics</literal> respectively.
 </para>
-<para>An instance of <literal>Typeable</literal> can only be derived if the
-data type has seven or fewer type parameters, all of kind <literal>*</literal>.
-The reason for this is that the <literal>Typeable</literal> class is derived using the scheme
-described in
-<ulink url="http://research.microsoft.com/%7Esimonpj/papers/hmap/gmap2.ps">
-Scrap More Boilerplate: Reflection, Zips, and Generalised Casts
-</ulink>.
-(Section 7.4 of the paper describes the multiple <literal>Typeable</literal> classes that
-are used, and only <literal>Typeable1</literal> up to
-<literal>Typeable7</literal> are provided in the library.)
-In other cases, there is nothing to stop the programmer writing a <literal>TypeableX</literal>
-class, whose kind suits that of the data type constructor, and
-then writing the data type instance by hand.
+<para>Since GHC 7.8.1, <literal>Typeable</literal> is kind-polymorphic (see
+<xref linkend="kind-polymorphism"/>) and can be derived for any datatype and
+type class. Instances for datatypes can be derived by attaching a 
+<literal>deriving Typeable</literal> clause to the datatype declaration, or by
+using standalone deriving (see <xref linkend="stand-alone-deriving"/>).
+Instances for type classes can only be derived using standalone deriving.
+Additionally, <option>-XAutoDeriveTypeable</option> will trigger the generation
+of derived <literal>Typeable</literal> instances for every datatype and type
+class declaration in the module it is used.
+</para>
+<para>
+Also since GHC 7.8.1, handwritten (ie. not derived) instances of
+<literal>Typeable</literal> are forbidden, and will be ignored with a warning.
 </para>
 </listitem>
 
diff --git a/docs/users_guide/using.xml b/docs/users_guide/using.xml
index 6574e9ecf3..be7e3da2ce 100644
--- a/docs/users_guide/using.xml
+++ b/docs/users_guide/using.xml
@@ -956,8 +956,9 @@ test.hs:(5,4)-(6,7):
     <option>-fwarn-missing-methods</option>,
     <option>-fwarn-lazy-unlifted-bindings</option>,
     <option>-fwarn-wrong-do-bind</option>,
-    <option>-fwarn-unsupported-calling-conventions</option>, and
-    <option>-fwarn-dodgy-foreign-imports</option>.  The following
+    <option>-fwarn-unsupported-calling-conventions</option>,
+    <option>-fwarn-dodgy-foreign-imports</option>, and
+    <option>-fwarn-typeable-instances</option>.  The following
     flags are
     simple ways to select standard &ldquo;packages&rdquo; of warnings:
     </para>
@@ -1682,6 +1683,19 @@ f "2"    = 2
         </listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><option>-fwarn-typeable-instances</option>:</term>
+        <listitem>
+          <indexterm><primary><option>-fwarn-typeable-instances</option></primary></indexterm>
+          <indexterm><primary>typeable instances, warning</primary></indexterm>
+
+          <para>Report handwritten (ie. not derived) instances of the
+          <literal>Typeable</literal> class. These are ignore by the compiler;
+          only derived instances of <literal>Typeable</literal> are allowed.
+          </para>
+        </listitem>
+      </varlistentry>
+
     </variablelist>
 
     <para>If you're feeling really paranoid, the