X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=docs%2Fusers_guide%2Fglasgow_exts.xml;h=9c1b2c7a789e9524afdf68ac03cbe9e0226deb74;hb=d5019cfeeaa33967d19146e235722b953e1d800f;hp=8a213683e4edfdd881f2acdb97b9ddfbebdac50b;hpb=f2dcf256399e9a2de6343c625630b51f8abf4863;p=ghc-hetmet.git

diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index 8a21368..9c1b2c7 100644
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -617,7 +617,7 @@ clunky env var1 var1 = case lookup env var1 of
     Nothing -> fail
     Just val2 -> val1 + val2
 where
-  fail = val1 + val2
+  fail = var1 + var2
 </programlisting>
 
 <para>
@@ -2107,7 +2107,9 @@ can be modified by two flags: <option>-fallow-overlapping-instances</option>
 </primary></indexterm> 
 and <option>-fallow-incoherent-instances</option>
 <indexterm><primary>-fallow-incoherent-instances
-</primary></indexterm>, as this section discusses.</para>
+</primary></indexterm>, as this section discusses.  Both these
+flags are dynamic flags, and can be set on a per-module basis, using 
+an <literal>OPTIONS_GHC</literal> pragma if desired (<xref linkend="source-file-options"/>).</para>
 <para>
 When GHC tries to resolve, say, the constraint <literal>C Int Bool</literal>,
 it tries to match every instance declaration against the
@@ -4236,7 +4238,46 @@ Hello
 </programlisting>
 
 </sect2>
+
+<sect2>
+<title>Using Template Haskell with Profiling</title>
+<indexterm><primary>profiling</primary><secondary>with Template Haskell</secondary></indexterm>
  
+<para>Template Haskell relies on GHC's built-in bytecode compiler and
+interpreter to run the splice expressions.  The bytecode interpreter
+runs the compiled expression on top of the same runtime on which GHC
+itself is running; this means that the compiled code referred to by
+the interpreted expression must be compatible with this runtime, and
+in particular this means that object code that is compiled for
+profiling <emphasis>cannot</emphasis> be loaded and used by a splice
+expression, because profiled object code is only compatible with the
+profiling version of the runtime.</para>
+
+<para>This causes difficulties if you have a multi-module program
+containing Template Haskell code and you need to compile it for
+profiling, because GHC cannot load the profiled object code and use it
+when executing the splices.  Fortunately GHC provides a workaround.
+The basic idea is to compile the program twice:</para>
+
+<orderedlist>
+<listitem>
+  <para>Compile the program or library first the normal way, without
+  <option>-prof</option><indexterm><primary><option>-prof</option></primary></indexterm>.</para>
+</listitem>
+<listitem>
+  <para>Then compile it again with <option>-prof</option>, and
+  additionally use <option>-osuf
+  p_o</option><indexterm><primary><option>-osuf</option></primary></indexterm>
+  to name the object files differentliy (you can choose any suffix
+  that isn't the normal object suffix here).  GHC will automatically
+  load the object files built in the first step when executing splice
+  expressions.  If you omit the <option>-osuf</option> flag when
+  building with <option>-prof</option> and Template Haskell is used,
+  GHC will emit an error message. </para>
+</listitem>
+</orderedlist>
+</sect2>
+
 </sect1>
 
 <!-- ===================== Arrow notation ===================  -->
@@ -5339,7 +5380,9 @@ The programmer can specify rewrite rules as part of the source program
 (in a pragma).  GHC applies these rewrite rules wherever it can, provided (a) 
 the <option>-O</option> flag (<xref linkend="options-optimise"/>) is on, 
 and (b) the <option>-frules-off</option> flag
-(<xref linkend="options-f"/>) is not specified.
+(<xref linkend="options-f"/>) is not specified, and (c) the
+<option>-fglasgow-exts</option> (<xref linkend="options-language"/>)
+flag is active.
 </para>
 
 <para>