Fix Trac #2246; overhaul handling of overloaded literals

The real work of fixing Trac #2246 is to use shortCutLit in
MatchLit.dsOverLit, so that type information discovered late in the
day by the type checker can still be exploited during desugaring.

However, as usual I found myself doing some refactoring along the
way, to tidy up the handling of overloaded literals.   The main
change is to split HsOverLit into a record, which in turn uses
a sum type for the three variants.  This makes the code significantly
more modular.

data HsOverLit id
  = OverLit {
	ol_val :: OverLitVal, 
	ol_rebindable :: Bool,		-- True <=> rebindable syntax
					-- False <=> standard syntax
	ol_witness :: SyntaxExpr id,	-- Note [Overloaded literal witnesses]
	ol_type :: PostTcType }

data OverLitVal
  = HsIntegral   !Integer   	-- Integer-looking literals;
  | HsFractional !Rational   	-- Frac-looking literals
  | HsIsString   !FastString 	-- String-looking literals

1 files changed, 5 insertions, 5 deletions

diff --git a/compiler/deSugar/Check.lhs b/compiler/deSugar/Check.lhs
index 75186feecb..c5b13eb2d3 100644
--- a/compiler/deSugar/Check.lhs
+++ b/compiler/deSugar/Check.lhs
@@ -433,11 +433,11 @@ get_lit :: Pat id -> Maybe HsLit
 -- Get a representative HsLit to stand for the OverLit
 -- It doesn't matter which one, because they will only be compared
 -- with other HsLits gotten in the same way
-get_lit (LitPat lit)			 = Just lit
-get_lit (NPat (HsIntegral i   _ _) mb _) = Just (HsIntPrim   (mb_neg mb i))
-get_lit (NPat (HsFractional f _ _) mb _) = Just (HsFloatPrim (mb_neg mb f))
-get_lit (NPat (HsIsString s   _ _)  _ _) = Just (HsStringPrim s)
-get_lit _                                = Nothing
+get_lit (LitPat lit)				          = Just lit
+get_lit (NPat (OverLit { ol_val = HsIntegral i})    mb _) = Just (HsIntPrim   (mb_neg mb i))
+get_lit (NPat (OverLit { ol_val = HsFractional f }) mb _) = Just (HsFloatPrim (mb_neg mb f))
+get_lit (NPat (OverLit { ol_val = HsIsString s })   _  _) = Just (HsStringPrim s)
+get_lit _                                	          = Nothing
 
 mb_neg :: Num a => Maybe b -> a -> a
 mb_neg Nothing  v = v