That should not happen. Can you boil out a test case and make a Trac ticket? When I try the same thing it works: Spec.hs: f :: Num a => a -> a {-# SPECIALISE f :: Int -> Int #-} f x = x+2 ghc -c -ddump-rules -O Spec.hs ==================== Top-level specialisations ==================== "SPEC Foo.f" ALWAYS forall {$dNum :: GHC.Num.Num GHC.Types.Int} Foo.f @ GHC.Types.Int $dNum = f Note the quantification over $dNum. Simon | -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users- | bounces@haskell.org] On Behalf Of Malcolm Wallace | Sent: 11 February 2009 16:58 | To: glasgow-haskell-users@haskell.org | Subject: bug in ghc specialiser? | | Here is an apparent bug in ghc's specialisation rules. The rewrite rule | generated by a SPECIALISE pragma seems to want to pattern-match on exact | dictionaries (as well as types). But the compiler is not necessarily | able to fully resolve dictionaries before the rules are supposed to | fire. | | First, the source code we want to specialise: | | {-# SPECIALISE | hedgehog :: Float -> Vector3 Float | -> [Cell_8 (Coord3 Float)] | -> [Cell_8 (Vector3 Float)] | -> [(Coord3 Float, Coord3 Float)] | #-} | hedgehog :: ( Fractional a, Cell cell vert, Eq vert | , Geom coord, Geom vector, Embed vector coord ) => | a -> vector a | -> [cell (coord a)] | -> [cell (vector a)] | -> [(coord a, coord a)] | | And the core + interface generated for this module contains the rule: | | "SPEC Hedgehog.hedgehog" ALWAYS forall | Hedgehog.hedgehog @ GHC.Float.Float | @ RectGrid.Cell_8 | @ CellTypes.MyVertex | @ Geometries.Coord3 | @ Graphics.Rendering.OpenGL.GL.CoordTrans.Vector3 | GHC.Float.$f16 | RectGrid.$f2 | CellTypes.$f1 | Geometries.$f5 | Geometries.$f3 | Geometries.$f1 | = Hedgehog.hedgehog1 | | But in a different module, here is what the usage site looks like just | before the specialisation rules are supposed to fire: | | hedgehog_a4wy = | Hedgehog.hedgehog | @ GHC.Float.Float | @ RectGrid.Cell_8 | @ CellTypes.MyVertex | @ Geometries.Coord3 | @ Graphics.Rendering.OpenGL.GL.CoordTrans.Vector3 | $dFractional_a4xP | RectGrid.$f2 | CellTypes.$f1 | (Dataset.$p2Embed | @ Graphics.Rendering.OpenGL.GL.CoordTrans.Vector3 | @ Geometries.Coord3 | Geometries.$f1) | (Dataset.$p1Embed | @ Graphics.Rendering.OpenGL.GL.CoordTrans.Vector3 | @ Geometries.Coord3 | Geometries.$f1) | Geometries.$f1 | | Notice how there are several dictionary selector functions sitting | there, so although some of the dictionaries match, not all do, and the | rule does not fire. However, later the worker-wrapper transformation | is able to resolve those outstanding dictionaries, giving: | | hedgehog_a4wy = | Hedgehog.$whedgehog | @ GHC.Float.Float | @ RectGrid.Cell_8 | @ CellTypes.MyVertex | @ Geometries.Coord3 | @ Graphics.Rendering.OpenGL.GL.CoordTrans.Vector3 | GHC.Float.$f16 | RectGrid.$f2 | Geometries.$f5 | Geometries.$f3 | Geometries.$f1 | | So I'm left calling the worker for the polymorphic version of the | function, rather than the specialised monomorphic code I wanted. Given | how many dictionaries are involved, and that this is the inner loop of | the program, I'm hoping there is a big performance win waiting for me, | if only I can get that specialised code to run! | | Regards, | Malcolm | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users