From e79e580be5d3d7caed73dec9e5a72b244cd1cc39 Mon Sep 17 00:00:00 2001
From: Simon Peyton Jones <simonpj@microsoft.com>
Date: Wed, 4 May 2011 12:05:42 +0100
Subject: [PATCH] Fix Trac #5117: desugar literal patterns consistencly

---
 compiler/deSugar/Check.lhs    |   16 ++++++++--------
 compiler/deSugar/Match.lhs    |    2 +-
 compiler/deSugar/MatchLit.lhs |   14 ++++++++++----
 3 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/compiler/deSugar/Check.lhs b/compiler/deSugar/Check.lhs
index 2432051..3d3aa4f 100644
--- a/compiler/deSugar/Check.lhs
+++ b/compiler/deSugar/Check.lhs
@@ -671,8 +671,6 @@ tidy_pat (CoPat _ pat _)  = tidy_pat pat
 tidy_pat (NPlusKPat id _ _ _) = WildPat (idType (unLoc id))
 tidy_pat (ViewPat _ _ ty)     = WildPat ty
 
-tidy_pat (NPat lit mb_neg eq) = tidyNPat lit mb_neg eq
-
 tidy_pat pat@(ConPatOut { pat_con = L _ id, pat_args = ps })
   = pat { pat_args = tidy_con id ps }
 
@@ -696,16 +694,18 @@ tidy_pat (TuplePat ps boxity ty)
   where
     arity = length ps
 
--- Unpack string patterns fully, so we can see when they overlap with
--- each other, or even explicit lists of Chars.
-tidy_pat (LitPat lit)
+tidy_pat (NPat lit mb_neg eq) = tidyNPat tidy_lit_pat lit mb_neg eq
+tidy_pat (LitPat lit)         = tidy_lit_pat lit
+
+tidy_lit_pat :: HsLit -> Pat Id
+-- Unpack string patterns fully, so we can see when they 
+-- overlap with each other, or even explicit lists of Chars.
+tidy_lit_pat lit
   | HsString s <- lit
-  = unLoc $ foldr (\c pat -> mkPrefixConPat consDataCon [mk_char_lit c, pat] stringTy)
+  = unLoc $ foldr (\c pat -> mkPrefixConPat consDataCon [mkCharLitPat c, pat] stringTy)
 		  (mkPrefixConPat nilDataCon [] stringTy) (unpackFS s)
   | otherwise
   = tidyLitPat lit 
-  where
-    mk_char_lit c = mkPrefixConPat charDataCon [nlLitPat (HsCharPrim c)] charTy
 
 -----------------
 tidy_con :: DataCon -> HsConPatDetails Id -> HsConPatDetails Id
diff --git a/compiler/deSugar/Match.lhs b/compiler/deSugar/Match.lhs
index 5c6b224..15c5a55 100644
--- a/compiler/deSugar/Match.lhs
+++ b/compiler/deSugar/Match.lhs
@@ -522,7 +522,7 @@ tidy1 _ (LitPat lit)
 
 -- NPats: we *might* be able to replace these w/ a simpler form
 tidy1 _ (NPat lit mb_neg eq)
-  = return (idDsWrapper, tidyNPat lit mb_neg eq)
+  = return (idDsWrapper, tidyNPat tidyLitPat lit mb_neg eq)
 
 -- BangPatterns: Pattern matching is already strict in constructors,
 -- tuples etc, so the last case strips off the bang for thoses patterns.
diff --git a/compiler/deSugar/MatchLit.lhs b/compiler/deSugar/MatchLit.lhs
index 5e5e81d..be112e0 100644
--- a/compiler/deSugar/MatchLit.lhs
+++ b/compiler/deSugar/MatchLit.lhs
@@ -152,8 +152,14 @@ tidyLitPat (HsString s)
 tidyLitPat lit = LitPat lit
 
 ----------------
-tidyNPat :: HsOverLit Id -> Maybe (SyntaxExpr Id) -> SyntaxExpr Id -> Pat Id
-tidyNPat (OverLit val False _ ty) mb_neg _
+tidyNPat :: (HsLit -> Pat Id)	-- How to tidy a LitPat
+	    	 -- We need this argument because tidyNPat is called
+		 -- both by Match and by Check, but they tidy LitPats 
+		 -- slightly differently; and we must desugar 
+		 -- literals consistently (see Trac #5117)
+         -> HsOverLit Id -> Maybe (SyntaxExpr Id) -> SyntaxExpr Id 
+         -> Pat Id
+tidyNPat tidy_lit_pat (OverLit val False _ ty) mb_neg _
 	-- False: Take short cuts only if the literal is not using rebindable syntax
 	-- 
 	-- Once that is settled, look for cases where the type of the 
@@ -169,7 +175,7 @@ tidyNPat (OverLit val False _ ty) mb_neg _
   | isWordTy ty,   Just int_lit <- mb_int_lit = mk_con_pat wordDataCon   (HsWordPrim   int_lit)
   | isFloatTy ty,  Just rat_lit <- mb_rat_lit = mk_con_pat floatDataCon  (HsFloatPrim  rat_lit)
   | isDoubleTy ty, Just rat_lit <- mb_rat_lit = mk_con_pat doubleDataCon (HsDoublePrim rat_lit)
-  | isStringTy ty, Just str_lit <- mb_str_lit = tidyLitPat (HsString str_lit)
+  | isStringTy ty, Just str_lit <- mb_str_lit = tidy_lit_pat (HsString str_lit)
   where
     mk_con_pat :: DataCon -> HsLit -> Pat Id
     mk_con_pat con lit = unLoc (mkPrefixConPat con [noLoc $ LitPat lit] ty)
@@ -193,7 +199,7 @@ tidyNPat (OverLit val False _ ty) mb_neg _
 		   (Nothing, HsIsString s) -> Just s
 		   _ -> Nothing
 
-tidyNPat over_lit mb_neg eq 
+tidyNPat _ over_lit mb_neg eq 
   = NPat over_lit mb_neg eq
 \end{code}
 
-- 
1.7.10.4