FIX #2395 (ViewPatterns trigger bad Check errors)

[ghc-hetmet.git] / compiler / hsSyn / HsPat.lhs

diff --git a/compiler/hsSyn/HsPat.lhs b/compiler/hsSyn/HsPat.lhs
index 84eadb7..3df0160 100644 (file)
--- 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