[commit: dph] master: Document the awful fake dependency hack in Data.Array.Parallel (15e2528)

[Ben Lippmeier]

Repository : ssh://darcs.haskell.org//srv/darcs/packages/dph

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/15e25288c247869c77d902e01810306a8cb5cc02

>---------------------------------------------------------------

commit 15e25288c247869c77d902e01810306a8cb5cc02
Author: Ben Lippmeier <benl at ouroborus.net>
Date:   Thu May 12 20:17:52 2011 +1000

    Document the awful fake dependency hack in Data.Array.Parallel

>---------------------------------------------------------------

 dph-common/Data/Array/Parallel.hs |   26 +++++++++++++++++++++++---
 1 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/dph-common/Data/Array/Parallel.hs b/dph-common/Data/Array/Parallel.hs
index d201f7a..e849551 100644
--- a/dph-common/Data/Array/Parallel.hs
+++ b/dph-common/Data/Array/Parallel.hs
@@ -53,12 +53,32 @@ module Data.Array.Parallel (
 import Prelude hiding (undefined)
 import GHC.PArr     -- only has the definition of [::] left
 
--- fake dependency to satisfy built-in iface loading in the vectoriser
-import Data.Array.Parallel.Prelude.Base.Tuple ()
-
 import Data.Array.Parallel.Lifted
 import Data.Array.Parallel.Lifted.Combinators
 
+
+-------------------------------------------------------------------------------
+-- FAKE DEPENDENCIES
+--  These imports are an atrocious hack to get around a race in the GHC build
+--  system. The race happens when we try to build Haddock docs for the dph-par
+--  and dph-seq packages. As these are really aliases for dph-common, all the
+--  dph-common modules need to be loaded, otherwise desugaring fails.
+--
+--  Adding these dependencies fixes the problem, as they ensure that the required
+--  dph-common modules are loaded before we try to vectorise THIS MODULE. If you 
+--  take them out, then mae sure GHC still validates with >= 2 threads. Without
+--  the dependencies it'll still work for 1 thread, but die with more than that.
+-- 
+--  Note that following modules are exactly the ones that don't import THIS MODULE
+--  by themselves. 
+-- 
+import Data.Array.Parallel.Prelude.Base.Bool    ()
+import Data.Array.Parallel.Prelude.Base.Tuple   ()
+--
+--  ... the horror, the horror ...
+-------------------------------------------------------------------------------
+
+
 infixl 9 !:
 infixr 5 +:+