X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FhsSyn%2FHsPat.lhs;h=aa1568d27fe1066cb8dd5ffe1699b471e779cbd4;hb=8053aac536c96dabdc06e9f068852f5481474a29;hp=5bb443b8e37c29f660335c884b4a871f66b84980;hpb=108361d05dfb0aa37871c2c6a4ddec45a1b68010;p=ghc-hetmet.git

diff --git a/compiler/hsSyn/HsPat.lhs b/compiler/hsSyn/HsPat.lhs
index 5bb443b..aa1568d 100644
--- a/compiler/hsSyn/HsPat.lhs
+++ b/compiler/hsSyn/HsPat.lhs
@@ -22,7 +22,8 @@ module HsPat (
 import {-# SOURCE #-} HsExpr		( SyntaxExpr )
 
 -- friends:
-import HsBinds		( DictBinds, HsBind(..), ExprCoFn, isIdCoercion, emptyLHsBinds, pprLHsBinds )
+import HsBinds		( DictBinds, HsBind(..), ExprCoFn, isIdCoercion, pprCoFn,
+			  emptyLHsBinds, pprLHsBinds )
 import HsLit		( HsLit(HsCharPrim), HsOverLit )
 import HsTypes		( LHsType, PostTcType )
 import BasicTypes	( Boxity, tupleParens )
@@ -121,14 +122,16 @@ data Pat id
 
 	------------ Dictionary patterns (translation only) ---------------
   | DictPat	    -- Used when destructing Dictionaries with an explicit case
-		    [id]			-- superclass dicts
-		    [id]			-- methods
+		    [id]		-- Superclass dicts
+		    [id]		-- Methods
 
 	------------ Pattern coercions (translation only) ---------------
   | CoPat 	ExprCoFn		-- If co::t1 -> t2, p::t2, 
 					-- then (CoPat co p) :: t1
-		(Pat id)		-- No nested location reqd
-	    	Type	
+		(Pat id)		-- Why not LPat?  Ans: existing locn will do
+	    	Type
+	-- During desugaring a (CoPat co pat) turns into a cast with 'co' on 
+	-- the scrutinee, followed by a match on 'pat'
 \end{code}
 
 HsConDetails is use both for patterns and for data type declarations
@@ -192,7 +195,7 @@ pprPat (NPat l Nothing  _ _)  = ppr l
 pprPat (NPat l (Just _) _ _)  = char '-' <> ppr l
 pprPat (NPlusKPat n k _ _)    = hcat [ppr n, char '+', ppr k]
 pprPat (TypePat ty)	      = ptext SLIT("{|") <> ppr ty <> ptext SLIT("|}")
-pprPat (CoPat co pat _)	      = parens (ppr co) <+> ptext SLIT("`cast`") <+> ppr pat
+pprPat (CoPat co pat _)	      = parens (pprCoFn (ppr pat) co)
 pprPat (SigPatIn pat ty)      = ppr pat <+> dcolon <+> ppr ty
 pprPat (SigPatOut pat ty)     = ppr pat <+> dcolon <+> ppr ty
 pprPat (DictPat ds ms)	      = parens (sep [ptext SLIT("{-dict-}"),