X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;ds=sidebyside;f=Data%2FDynamic.hs;h=761f55f150679140c66eed315cb9330d4483c5c8;hb=26d2805a6e58822d246cf9601fb226b0861e7f65;hp=f02290a4769bb31be13c9361cf034752bea0faa8;hpb=aaf764b3ad8b1816d68b5f27299eac125f08e1a5;p=haskell-directory.git

diff --git a/Data/Dynamic.hs b/Data/Dynamic.hs
index f02290a..761f55f 100644
--- a/Data/Dynamic.hs
+++ b/Data/Dynamic.hs
@@ -34,7 +34,8 @@ module Data.Dynamic
 	
 	-- * Applying functions of dynamic type
 	dynApply,
-	dynApp
+	dynApp,
+        dynTypeRep
 
   ) where
 
@@ -98,16 +99,14 @@ instance Show Dynamic where
 	  showString ">>"
 
 #ifdef __GLASGOW_HASKELL__
-type Obj = forall a . a
- -- Dummy type to hold the dynamically typed value.
+type Obj = Any
+ -- Use GHC's primitive 'Any' type to hold the dynamically typed value.
  --
- -- In GHC's new eval/apply execution model this type must
- -- be polymorphic.  It can't be a constructor, because then
- -- GHC will use the constructor convention when evaluating it,
- -- and this will go wrong if the object is really a function.  On
- -- the other hand, if we use a polymorphic type, GHC will use
+ -- In GHC's new eval/apply execution model this type must not look
+ -- like a data type.  If it did, GHC would use the constructor convention 
+ -- when evaluating it, and this will go wrong if the object is really a 
+ -- function.  Using Any forces GHC to use
  -- a fallback convention for evaluating it that works for all types.
- -- (using a function type here would also work).
 #elif !defined(__HUGS__)
 data Obj = Obj
 #endif
@@ -162,3 +161,6 @@ dynApp f x = case dynApply f x of
              Nothing -> error ("Type error in dynamic application.\n" ++
                                "Can't apply function " ++ show f ++
                                " to argument " ++ show x)
+
+dynTypeRep :: Dynamic -> TypeRep
+dynTypeRep (Dynamic tr _) = tr