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 http://hackage.haskell.org/trac/ghc/browser/includes/rts/storage/InfoTables.... 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 http://www.mega-nerd.com/
Erik de Castro Lopo
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
http://hackage.haskell.org/trac/ghc/browser/includes/rts/storage/InfoTables....
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
Unfortunately I'm not sure that the sort of polymorphism that you need is possible at the moment. To see why, consider a few of the kinds that this function as-written might take, 1. Double# :: TYPE 'DoubleRep 2. Int :: TYPE 'LiftedRep 3. Array# :: TYPE 'UnliftedRep What you want here, I believe, is to allow getClosureData to accept (2) and (3). This should in principle be fine; afterall they are both represented at runtime by a pointer. However, (1) has a much different representation (being passed in a floating point register) and currently we can't distinguish (1) from (2) and (3) in the kind system. Consequently, we aren't able to provide this sort of sort of polymorphism since there is no single calling convention that could be used with such a function. At the moment I think the best you could do would be to provide an implementation for each supported RuntimeRep (either multiple functions or typeclass overloaded). Cheers, - Ben
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
participants (3)
-
Ben Gamari -
Erik de Castro Lopo -
Simon Peyton Jones