[commit: ghc] type-holes-branch: Add a flag to turn (unnamed) holes on. (03fb603)

[Simon Peyton Jones]

Repository : ssh://darcs.haskell.org//srv/darcs/ghc

On branch  : type-holes-branch

http://hackage.haskell.org/trac/ghc/changeset/03fb6039c4e57c9cf92bcb8f0c0682c49c9f0897

>---------------------------------------------------------------

commit 03fb6039c4e57c9cf92bcb8f0c0682c49c9f0897
Author: Thijs Alkemade <thijsalkemade at gmail.com>
Date:   Wed Jul 11 15:52:43 2012 +0200

    Add a flag to turn (unnamed) holes on.
    
    This is now -XHoles or {-# LANGUAGE Holes #-}. Named holes should probably be completely removed or disabled in the parser.

>---------------------------------------------------------------

 compiler/main/DynFlags.hs  |    4 +++-
 compiler/rename/RnExpr.lhs |    9 ++++++---
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/compiler/main/DynFlags.hs b/compiler/main/DynFlags.hs
index c04b474..4ae66e6 100644
--- a/compiler/main/DynFlags.hs
+++ b/compiler/main/DynFlags.hs
@@ -461,6 +461,7 @@ data ExtensionFlag
    | Opt_NondecreasingIndentation
    | Opt_RelaxedLayout
    | Opt_TraditionalRecordSyntax
+   | Opt_Holes
    deriving (Eq, Enum, Show)
 
 -- | Contains not only a collection of 'DynFlag's but also a plethora of
@@ -2058,7 +2059,8 @@ xFlags = [
   ( "OverlappingInstances",             Opt_OverlappingInstances, nop ),
   ( "UndecidableInstances",             Opt_UndecidableInstances, nop ),
   ( "IncoherentInstances",              Opt_IncoherentInstances, nop ),
-  ( "PackageImports",                   Opt_PackageImports, nop )
+  ( "PackageImports",                   Opt_PackageImports, nop ),
+  ( "Holes",                            Opt_Holes, nop )
   ]
 
 defaultFlags :: [DynFlag]
diff --git a/compiler/rename/RnExpr.lhs b/compiler/rename/RnExpr.lhs
index e7cc03b..d1719f2 100644
--- a/compiler/rename/RnExpr.lhs
+++ b/compiler/rename/RnExpr.lhs
@@ -305,9 +305,12 @@ Since all the symbols are reservedops we can simply reject them.
 We return a (bogus) EWildPat in each case.
 
 \begin{code}
-rnExpr e at EWildPat      = do { srcspan <- getSrcSpanM
-                            ; name' <- rnHoleName srcspan Nothing
-                            ; return (HsHole name', emptyFVs)
+rnExpr e at EWildPat      = do { holes <- xoptM Opt_Holes
+                            ; if holes then do { srcspan <- getSrcSpanM
+                                               ; name' <- rnHoleName srcspan Nothing
+                                               ; return (HsHole name', emptyFVs)
+                                               }
+                              else patSynErr e
                             }
 -- rnExpr e at EWildPat      = patSynErr e
 rnExpr e@(EAsPat {})   = patSynErr e