[GHC] #9357: Kind-polymorphic type family accepts unlifted type arguments
#9357: Kind-polymorphic type family accepts unlifted type arguments -------------------------------------+------------------------------------- Reporter: kosmikus | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.2 checker) | Operating System: Keywords: | Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: GHC Difficulty: Unknown | accepts invalid program Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- The following code is accepted by ghc-7.8.2 and ghc-7.6.3: {{{#!hs {-# LANGUAGE TypeFamilies, MagicHash, PolyKinds #-} import GHC.Exts type family F (a :: k) :: * type instance F Int# = () }}} In nearly all other places, it seems that unlifted types are explicitly forbidden. I'm also not allowed to actually apply `F` to `Int#` after defining the type family like this. So I think the compiler should probably reject the `type instance`. (BTW, is it actually clear that using `#` as an argument kind to a type family or as an index kind for a GADT is in any way harmful?) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9357 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#9357: Kind-polymorphic type family accepts unlifted type arguments
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Reporter: kosmikus | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.8.2
(Type checker) | Keywords:
Resolution: | Architecture: Unknown/Multiple
Operating System: | Difficulty: Unknown
Unknown/Multiple | Blocked By:
Type of failure: GHC | Related Tickets:
accepts invalid program |
Test Case: |
Blocking: |
Differential Revisions: |
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Comment (by Simon Peyton Jones
#9357: Kind-polymorphic type family accepts unlifted type arguments -------------------------------------+------------------------------------- Reporter: kosmikus | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 (Type checker) | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: GHC | Related Tickets: accepts invalid program | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by simonpj): Good point. It's not impossible that we could accept unboxed ''arguments'' to type families, but unbozed ''results'' would definitely be problematic: how many bits does it take to represent `(F Int)`? Is is held in an integer register or a floating point register. For now I've just made it so that we require a boxed monotype as both argument and result. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9357#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#9357: Kind-polymorphic type family accepts unlifted type arguments -------------------------------------+------------------------------------- Reporter: kosmikus | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 (Type checker) | Keywords: Resolution: fixed | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: GHC | Related Tickets: accepts invalid program | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Changes (by simonpj): * status: new => closed * resolution: => fixed -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9357#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#9357: Kind-polymorphic type family accepts unlifted type arguments -------------------------------------+------------------------------------- Reporter: kosmikus | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.2 checker) | Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC accepts | Unknown/Multiple invalid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): If Phab:D1807 is merged then this limitation will once again be lifted allowing. As it stands, this works, {{{#!hs {-# LANGUAGE PolyKinds TypeFamilies MagicHash DataKinds TypeInType #-} import GHC.Exts import GHC.Types class BoxIt (a :: TYPE 'Unlifted) where type Boxed a :: * boxed :: a -> Boxed a instance BoxIt Char# where type Boxed Char# = Char boxed x = C# x main :: IO () main = print $ boxed 'c'# }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9357#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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