Major refactoring of the way that UNPACK pragmas are handled

The situation was pretty dire.  The way in which data constructors
were handled, notably the mapping between their *source* argument types
and their *representation* argument types (after seq'ing and unpacking)
was scattered in three different places, and hard to keep in sync.

Now it is all in one place:

 * The dcRep field of a DataCon gives its representation,
   specified by a DataConRep

 * As well as having the wrapper, the DataConRep has a "boxer"
   of type DataConBoxer (defined in MkId for loopy reasons).
   The boxer used at a pattern match to reconstruct the source-level
   arguments from the rep-level bindings in the pattern match.

 * The unboxing in the wrapper and the boxing in the boxer are dual,
   and are now constructed together, by MkId.mkDataConRep. This is
   the key function of this change.

 * All the computeBoxingStrategy code in TcTyClsDcls disappears.

Much nicer.

There is a little bit of refactoring left to do; the strange
deepSplitProductType functions are now called only in WwLib, so
I moved them there, and I think they could be tidied up further.

1 files changed, 3 insertions, 3 deletions

diff --git a/compiler/deSugar/DsMeta.hs b/compiler/deSugar/DsMeta.hs
index 405b7687a5..f25039c8a9 100644
--- a/compiler/deSugar/DsMeta.hs
+++ b/compiler/deSugar/DsMeta.hs
@@ -519,9 +519,9 @@ repBangTy ty= do
   rep2 strictTypeName [s, t]
   where
     (str, ty') = case ty of
-		   L _ (HsBangTy HsUnpack ty) -> (unpackedName,  ty)
-		   L _ (HsBangTy _ ty)        -> (isStrictName,  ty)
-		   _                          -> (notStrictName, ty)
+		   L _ (HsBangTy (HsBang True) ty) -> (unpackedName,  ty)
+		   L _ (HsBangTy _ ty)             -> (isStrictName,  ty)
+		   _                               -> (notStrictName, ty)
 
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 -- 			Deriving clause