Suppose f1 :: forall (a :: TYPE LiftedPtrRep). a -> Closure f2 :: forall (a :: TYPE UnliftedPtrRep). a -> Closure f3 :: forall (a :: TYPE FloatRep). a -> Closure f3 takes its argument in a floating point register, whereas f1 and f2 take their arguments in a pointer register; so you can't have a function polymorphic in all three. See the paper (have you read it?) You might think that f1 and f2 are more compatible, since they both take a pointer, but consider the call f1 (g x) f2 (h x) For f1 we'll build a thunk for (g x) and pass it to f1. For f2 we'll evaluate (h x) and pass the result to f2. So the calls are different. In short, there is a good reason that we can't be polymorphic here. You'll have to use three different functions. Simon | -----Original Message----- | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Erik de | Castro Lopo | Sent: 05 February 2017 08:49 | To: ghc-devs@haskell.org | Subject: Handling of unlifted types | | Hi all, | | I'm working on pulling the core parts of Joachim Breitner's ghc-heap-view | library into GHC. The WIP Phab review is here: | | https://phabricator.haskell.org/D3055 | | Currently that library has a function: | | getClosureData :: a -> IO Closure | | which works fine for lifted types. However, some of the supported closure | types in | | | https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fhackage.hask | ell.org%2Ftrac%2Fghc%2Fbrowser%2Fincludes%2Frts%2Fstorage%2FInfoTables.h&dat | a=02%7C01%7Csimonpj%40microsoft.com%7Ca5585e761d5149d4f3c608d44da3f3dc%7C72f | 988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636218813965987006&sdata=5ze3nbAjXYm | Ey7H6M4Imtyz7dVH1bjEtloUJWQ2ItWo%3D&reserved=0 | | actually refer to unlifted types, like the `MUT_ARR_PTRS_*` and | `SMALL_MUT_ARR_PTRS_*`. | | I've had a look at the levity polymorphism stuff implemented in ghc 8.0 and | came up with a new type for `getClosureData`: | | getClosureData :: forall (r :: RuntimeRep) (a :: TYPE r). a -> IO | Closure | | but that results in: | | A representation-polymorphic type is not allowed here: | Type: a | Kind: TYPE r | In the type of binder ‘x’ | | Am I barking up the wrong tree here? Any one have a clue on how I might make | progress on this? | | | Erik | -- | ---------------------------------------------------------------------- | Erik de Castro Lopo | https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.mega- | nerd.com%2F&data=02%7C01%7Csimonpj%40microsoft.com%7Ca5585e761d5149d4f3c608d | 44da3f3dc%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636218813965987006&sd | ata=M8bvL%2BDEFYX7Sx%2FAipnRDBBtbFBMcAl7p3Rf86Hbe%2FA%3D&reserved=0 | _______________________________________________ | ghc-devs mailing list | ghc-devs@haskell.org | https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmail.haskell | .org%2Fcgi-bin%2Fmailman%2Flistinfo%2Fghc- | devs&data=02%7C01%7Csimonpj%40microsoft.com%7Ca5585e761d5149d4f3c608d44da3f3 | dc%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636218813965987006&sdata=9AQ | mgEerIRrUeT%2BBRrGriMiAm2oJ7F9mQrMrBAPCQq0%3D&reserved=0