Lazy patterns are like wild-cards for overlap warnings

	MERGE TO STABLE

Fixes Trac #827
Test is should_compiler/ds058

diff --git a/compiler/deSugar/Check.lhs b/compiler/deSugar/Check.lhs
index 9aac5ce..097a008 100644 (file)
--- a/compiler/deSugar/Check.lhs
+++ b/compiler/deSugar/Check.lhs
@@ -623,7 +623,8 @@ simplify_pat pat@(WildPat gt) = pat
 simplify_pat (VarPat id)      = WildPat (idType id) 
 simplify_pat (VarPatOut id _) = WildPat (idType id)    -- Ignore the bindings
 simplify_pat (ParPat p)       = unLoc (simplify_lpat p)
-simplify_pat (LazyPat p)      = unLoc (simplify_lpat p)
+simplify_pat (LazyPat p)      = WildPat (hsPatType p)  -- For overlap and exhaustiveness checking
+                                                       -- purposes, a ~pat is like a wildcard
 simplify_pat (BangPat p)      = unLoc (simplify_lpat p)
 simplify_pat (AsPat id p)     = unLoc (simplify_lpat p)
 simplify_pat (SigPatOut p _)  = unLoc (simplify_lpat p)        -- I'm not sure this is right