From cf924c1549880f9ada192d24342dc610dea1d727 Mon Sep 17 00:00:00 2001
From: Alexander Dunlap <alexander.dunlap@gmail.com>
Date: Fri, 7 Aug 2009 18:48:41 +0000
Subject: [PATCH] FIX #2395 (ViewPatterns trigger bad Check errors)

---
 compiler/deSugar/Check.lhs |    8 +++++---
 compiler/hsSyn/HsPat.lhs   |   33 ++++++++++++++++++++++++++++++++-
 2 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/compiler/deSugar/Check.lhs b/compiler/deSugar/Check.lhs
index 6244b37..ec72287 100644
--- a/compiler/deSugar/Check.lhs
+++ b/compiler/deSugar/Check.lhs
@@ -109,8 +109,12 @@ type EqnSet = UniqSet EqnNo
 
 check :: [EquationInfo] -> ([ExhaustivePat], [EquationInfo])
 	-- Second result is the shadowed equations
-check qs = (untidy_warns, shadowed_eqns)
+  -- if there are view patterns, just give up - don't know what the function is
+check qs | has_view_pattern = ([],[])
+         | otherwise = (untidy_warns, shadowed_eqns)
       where
+        is_view x = hasViewPat x
+        has_view_pattern = any (\(EqnInfo p _) -> any is_view p) qs
 	(warns, used_nos) = check' ([1..] `zip` map simplify_eqn qs)
 	untidy_warns = map untidy_exhaustive warns 
 	shadowed_eqns = [eqn | (eqn,i) <- qs `zip` [1..], 
@@ -218,8 +222,6 @@ check' qs
    | literals     = split_by_literals qs
    | constructors = split_by_constructor qs
    | only_vars    = first_column_only_vars qs
--- FIXME: hack to get view patterns through for now
-   | otherwise    = ([([],[])],emptyUniqSet)
 -- pprPanic "Check.check': Not implemented :-(" (ppr first_pats)
   where
      -- Note: RecPats will have been simplified to ConPats
diff --git a/compiler/hsSyn/HsPat.lhs b/compiler/hsSyn/HsPat.lhs
index 84eadb7..3df0160 100644
--- a/compiler/hsSyn/HsPat.lhs
+++ b/compiler/hsSyn/HsPat.lhs
@@ -25,7 +25,7 @@ module HsPat (
 
 	isBangHsBind, hsPatNeedsParens,
 	patsAreAllCons, isConPat, isSigPat, isWildPat,
-	patsAreAllLits,	isLitPat, isIrrefutableHsPat
+	patsAreAllLits,	isLitPat, isIrrefutableHsPat, hasViewPat
     ) where
 
 import {-# SOURCE #-} HsExpr		(SyntaxExpr, LHsExpr, pprLExpr)
@@ -369,6 +369,37 @@ patterns are treated specially, of course.
 
 The 1.3 report defines what ``irrefutable'' and ``failure-free'' patterns are.
 \begin{code}
+hasViewPat :: Pat id -> Bool
+hasViewPat p = hasViewPat' (L undefined p)
+
+hasViewPat' :: LPat id -> Bool
+hasViewPat' (L _ p) = go p where
+  go (WildPat _) = False
+  go (VarPat _) = False
+  go (VarPatOut _ _) = False
+  go (LazyPat p) = hasViewPat' p
+  go (AsPat _ p) = hasViewPat' p
+  go (ParPat p) = hasViewPat' p
+  go (BangPat p) = hasViewPat' p
+  go (ListPat p _) = any hasViewPat' p
+  go (TuplePat p _ _) = any hasViewPat' p
+  go (PArrPat p _) = any hasViewPat' p
+  go (ConPatIn _ p) = go' p
+  go (ConPatOut _ _ _ _ p _) = go' p
+  go (ViewPat _ _ _) = True
+  go (QuasiQuotePat _) = False
+  go (LitPat _) = False
+  go (NPat _ _ _) = False
+  go (NPlusKPat _ _ _ _) = False
+  go (TypePat _) = False
+  go (SigPatIn p _) = hasViewPat' p
+  go (SigPatOut p _) = hasViewPat' p
+  go (CoPat _ _ _) = False
+  go' p = case p of
+    PrefixCon ps -> any hasViewPat' ps
+    RecCon (HsRecFields fs _) -> any (hasViewPat' . hsRecFieldArg) fs
+    InfixCon p1 p2 -> hasViewPat' p1 || hasViewPat' p2
+
 isWildPat :: Pat id -> Bool
 isWildPat (WildPat _) = True
 isWildPat _           = False
-- 
1.7.10.4