[GHC] #15181: Levity Polymorphic type signatures in GHC.Prim
#15181: Levity Polymorphic type signatures in GHC.Prim -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Some of the type signatures in the haddocks for GHC.Prim are misleading. Here are a few: {{{ unsafeCoerce# :: a -> b mkWeak# :: o -> b -> (State# RealWorld -> (#State# RealWorld, c#)) -> State# RealWorld -> (#State# RealWorld, Weak# b#) raise# :: b -> o }}} The type signatures for these lead one to believe that all of the arguments must be **lifted** types, but this is not actually the case. For example, `raise#` is levity polymorphic in its returned value and should actually have the type: {{{ raise# :: forall (r :: RuntimeRep) (o :: TYPE r). b -> o }}} It's not just the haddocks that show an inaccurate type. Even in GHCi, we get this: {{{
:set -XMagicHash :set -fprint-explicit-kinds :set -fprint-explicit-runtime-reps import GHC.Exts :t raise# raise# :: b -> a }}}
Similarly, `unsafeCoerce#` is levity polymorphic in both types. Unfortunately, `mkWeak#` is more difficult to assign a correct type to. It should be possible for it to be broken into two separate functions (which each do the exact same thing), one of which operates on values of type `LiftedRep` and other on `UnliftedRep`. But this would be a breaking change, and it may not be worth the breakage it would introduce. At the very least, I feel like fixing `raise#` is worthwhile, since it wouldn't break anything. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15181 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15181: Levity Polymorphic type signatures in GHC.Prim -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Resolution: | Keywords: | LevityPolymorphism Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by andrewthad): * keywords: => LevityPolymorphism -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15181#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15181: Levity Polymorphic type signatures in GHC.Prim -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Resolution: duplicate | Keywords: | LevityPolymorphism Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #11786 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * status: new => closed * resolution: => duplicate * related: => #11786 Comment: Indeed. Note that the correct type signatures are actually displayed with `:info`: {{{ λ> :info raise# raise# :: forall b (q :: GHC.Types.RuntimeRep) (a :: TYPE q). b -> a -- Defined in ‘GHC.Prim’ λ> :info unsafeCoerce# unsafeCoerce# :: forall (k0 :: GHC.Types.RuntimeRep) (k1 :: GHC.Types.RuntimeRep) (a :: TYPE k0) (b :: TYPE k1). a -> b -- Defined in ‘GHC.Prim’ λ> :info mkWeak# mkWeak# :: forall (q :: GHC.Types.RuntimeRep) (a :: TYPE q) b c. a -> b -> (State# RealWorld -> (# State# RealWorld, c #)) -> State# RealWorld -> (# State# RealWorld, Weak# b #) -- Defined in ‘GHC.Prim’ }}} However, `:type` does not show the same thing with `-fprint-explicit- runtime-reps` enabled. In short, this is a pretty-printing issue with `:type`, the subject of #11786. I'll close this ticket in favor of that one. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15181#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15181: Levity Polymorphic type signatures in GHC.Prim -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Resolution: duplicate | Keywords: | LevityPolymorphism Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #11786 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by andrewthad): The haddocks are also inaccurate for these functions, which #11786 does not address. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15181#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15181: Levity Polymorphic type signatures in GHC.Prim -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Resolution: duplicate | Keywords: | LevityPolymorphism Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #11786 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): True, but that's a Haddock problem, not a GHC one. I'd encourage opening an instance at https://github.com/haskell/haddock/issues. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15181#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15181: Levity Polymorphic type signatures in GHC.Prim -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Resolution: duplicate | Keywords: | LevityPolymorphism Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #11786 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by andrewthad): I'll do that. Do you happen to you where in the GHC source the real type signatures of these are found? In primops.txt, https://ghc.haskell.org/trac/ghc/browser/ghc/compiler/prelude/primops.txt.pp..., which is where I had always assumed the type signatures came from, the types in the signature for `raise#` do not mention their true kinds. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15181#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15181: Levity Polymorphic type signatures in GHC.Prim -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Resolution: duplicate | Keywords: | LevityPolymorphism Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #11786 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by andrewthad): Haddock issue: https://github.com/haskell/haddock/issues/838 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15181#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15181: Levity Polymorphic type signatures in GHC.Prim -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Resolution: duplicate | Keywords: | LevityPolymorphism Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #11786 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): I'm not intimately familiar with the specifics, but I do know that `GHC.Prim` (and other code which adds magical properties to functions defined therein) is generated through the [http://git.haskell.org/ghc.git/tree/a32c8f7514c8192fa064537fb93d5a5c224991a0... genprimopcode] utility. `genprimopcode` has a convention that any type variable named `o` is levity polymorphic, so that's why `a -> o` gets a wired-in levity polymorphic type. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15181#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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