From a97ebe39e8b76ca1dad1e875609da89e81353c6e Mon Sep 17 00:00:00 2001
From: Simon Peyton Jones <simonpj@microsoft.com>
Date: Thu, 6 Jun 2013 14:36:56 +0100
Subject: [PATCH] Comments

---
 GHC/Exception.lhs-boot | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/GHC/Exception.lhs-boot b/GHC/Exception.lhs-boot
index 9c3b0bf4..f93d8067 100644
--- a/GHC/Exception.lhs-boot
+++ b/GHC/Exception.lhs-boot
@@ -1,3 +1,24 @@
+This SOURCE-imported hs-boot module cuts a big dependency loop:
+
+         GHC.Exception
+imports  Data.Maybe
+imports  GHC.Base
+imports  GHC.Err
+imports  {-# SOURCE #-} GHC.Exception
+
+More dramatically
+
+         GHC.Exception
+imports  Data.Typeable
+imports  Data.Typeable.Internals
+imports  GHC.Arr (fingerprint representation etc)
+imports  GHC.Real
+imports  {-# SOURCE #-} GHC.Exception
+
+However, GHC.Exceptions loop-breaking exports are all nice,
+well-behaved, non-bottom values.  The clients use 'raise#'
+to get a visibly-bottom value.
+
 \begin{code}
 {-# LANGUAGE Trustworthy #-}
 {-# LANGUAGE NoImplicitPrelude #-}
@@ -11,8 +32,6 @@ module GHC.Exception ( SomeException, errorCallException,
     ) where 
 import GHC.Types( Char )
 
--- These exports are nice, well-behaved, non-bottom values
-
 data SomeException
 divZeroException, overflowException, ratioZeroDenomException  :: SomeException
 errorCallException :: [Char] -> SomeException