[project @ 2003-05-30 09:04:28 by simonmar]

[ghc-hetmet.git] / ghc / docs / users_guide / bugs.sgml

diff --git a/ghc/docs/users_guide/bugs.sgml b/ghc/docs/users_guide/bugs.sgml
index 0d5fa2b..60cadd5 100644 (file)
--- a/ghc/docs/users_guide/bugs.sgml
+++ b/ghc/docs/users_guide/bugs.sgml
@@ -76,41 +76,18 @@
       <title>Expressions and patterns</title>
 
        <para>None known.</para>
-
     </sect3>
 
     <sect3 id="infelicities-decls">
       <title>Declarations and bindings</title>
 
       <para>None known.</para>
-
     </sect3>
       
       <sect3 id="infelicities-Modules">
        <title>Module system and interface files</title>
        
-       <variablelist>
-         <varlistentry>
-           <term><literal>Main</literal> module</term>
-           <listitem>
-             <para>GHC interprets the module header
-<programlisting>module Main where</programlisting>
-              as if it was
-<programlisting>module Main (main) where</programlisting>
-              </para>
-
-              <para>This change allows GHC to optimise slightly more
-              aggresively inside the <literal>Main</literal>
-              module.</para>
-
-              <para>You are highly unlikely to notice the difference, since
-              importing <literal>Main</literal> is very rare (it would
-              introduce a recursive module dependency, so doing it by
-              accident is unlikely too).</para>
-           </listitem>
-         </varlistentry>
-       </variablelist>
-
+       <para>None known.</para>
     </sect3>
 
     <sect3 id="infelicities-numbers">
@@ -306,6 +283,23 @@ main = print (array (1,1) [(1,2), (1,3)])</programlisting>
       </listitem>
     
       <listitem>
+       <para>GHC does not allow you to have a data type with a context 
+          that mentions type variables that are not data type parameters.
+         For example:
+<programlisting>
+  data C a b => T a = MkT a
+</programlisting>
+         so that <literal>MkT</literal>'s type is
+<programlisting>
+  MkT :: forall a b. C a b => a -> T a
+</programlisting>
+        In principle, with a suitable class declaration with a functional dependency,
+        it's possible that this type is not ambiguous; but GHC nevertheless rejects
+         it.  The type variables mentioned in the context of the data type declaration must
+       be among the type parameters of the data type.</para>
+      </listitem>
+
+      <listitem>
        <para>GHCi does not respect the <literal>default</literal>
         declaration in the module whose scope you are in.  Instead,
         for expressions typed at the command line, you always get the