July 2017 - ghc-tickets

[GHC] #13601: GHC errors but hangs
by GHC 28 Jul '17

28 Jul '17

#13601: GHC errors but hangs -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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: -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE TypeFamilies, DataKinds, TypeInType #-} import GHC.Exts import Prelude (Bool(True,False),Integer,Ordering,undefined) import qualified Prelude import Data.Kind -------------------- -- class hierarchy type family Rep (rep :: RuntimeRep) :: RuntimeRep where -- Rep IntRep = IntRep -- Rep DoubleRep = IntRep -- Rep PtrRepUnlifted = IntRep -- Rep PtrRepLifted = PtrRepLifted class Boolean (Logic a) => Eq (a :: TYPE rep) where type Logic (a :: TYPE rep) :: TYPE (Rep rep) (==) :: a -> a -> Logic a class Eq a => POrd (a :: TYPE rep) where inf :: a -> a -> a class POrd a => MinBound (a :: TYPE rep) where minBound :: () -> a class POrd a => Lattice (a :: TYPE rep) where sup :: a -> a -> a class (Lattice a, MinBound a) => Bounded (a :: TYPE rep) where maxBound :: () -> a class Bounded a => Complemented (a :: TYPE rep) where not :: a -> a class Bounded a => Heyting (a :: TYPE rep) where infixr 3 ==> (==>) :: a -> a -> a class (Complemented a, Heyting a) => Boolean a (||) :: Boolean a => a -> a -> a (||) = sup (&&) :: Boolean a => a -> a -> a (&&) = inf }}} hangs with {{{ $ ghci a.hs GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( a.hs, interpreted ) a.hs:18:16: error: C-c C-cInterrupted. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13601> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13780: Nightmarish pretty-printing of equality type in GHC 8.2 error message
by GHC 28 Jul '17

28 Jul '17

#13780: Nightmarish pretty-printing of equality type in GHC 8.2 error message -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 (Type checker) | Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I originally spotted this in https://ghc.haskell.org/trac/ghc/ticket/12102#comment:1, but I happened to stumble upon it again recently in a separate context, so I though it deserved its own ticket. Here's some code which does not typecheck: {{{#!hs {-# LANGUAGE ExistentialQuantification #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeInType #-} module Foo where data family Sing (a :: k) data Foo a = a ~ Bool => MkFoo data instance Sing (z :: Foo a) = (z ~ MkFoo) => SMkFoo }}} In GHC 8.0.1 and 8.0.2, the error message you'd get from this program was reasonable enough: {{{ GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Foo ( Bug.hs, interpreted ) Bug.hs:9:40: error: • Expected kind ‘Foo a’, but ‘'MkFoo’ has kind ‘Foo Bool’ • In the second argument of ‘~’, namely ‘MkFoo’ In the definition of data constructor ‘SMkFoo’ In the data instance declaration for ‘Sing’ }}} But in GHC 8.2.1 and HEAD, it's hair-raisingly bad: {{{ GHCi, version 8.2.0.20170522: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Foo ( Bug.hs, interpreted ) Bug.hs:9:40: error: • Expected kind ‘Foo a’, but ‘'MkFoo ('Data.Type.Equality.C:~ ('GHC.Types.Eq# <>))’ has kind ‘Foo Bool’ • In the second argument of ‘~’, namely ‘MkFoo’ In the definition of data constructor ‘SMkFoo’ In the data instance declaration for ‘Sing’ | 9 | data instance Sing (z :: Foo a) = (z ~ MkFoo) => SMkFoo | ^^^^^ }}} **WAT.** -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13780> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13877: GHC panic: No skolem info: k2
by GHC 28 Jul '17

28 Jul '17

#13877: GHC panic: No skolem info: k2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following code causes a GHC panic on GHC 8.0.1, 8.0.2, 8.2.1, and HEAD: {{{#!hs {-# LANGUAGE AllowAmbiguousTypes #-} {-# LANGUAGE ConstraintKinds #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE Trustworthy #-} {-# LANGUAGE TypeApplications #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeInType #-} {-# LANGUAGE TypeOperators #-} module Eliminator where import Data.Kind data family Sing (a :: k) data instance Sing (z :: [a]) where SNil :: Sing '[] SCons :: Sing x -> Sing xs -> Sing (x:xs) data TyFun :: * -> * -> * type a ~> b = TyFun a b -> * infixr 0 ~> type family Apply (f :: k1 ~> k2) (x :: k1) :: k2 type a @@ b = Apply a b infixl 9 @@ data FunArrow = (:->) | (:~>) class FunType (arr :: FunArrow) where type Fun (k1 :: Type) arr (k2 :: Type) :: Type class FunType arr => AppType (arr :: FunArrow) where type App k1 arr k2 (f :: Fun k1 arr k2) (x :: k1) :: k2 type FunApp arr = (FunType arr, AppType arr) instance FunType (:->) where type Fun k1 (:->) k2 = k1 -> k2 $(return []) -- This is only necessary for GHC 8.0 -- GHC 8.2 is smarter instance AppType (:->) where type App k1 (:->) k2 (f :: k1 -> k2) x = f x instance FunType (:~>) where type Fun k1 (:~>) k2 = k1 ~> k2 $(return []) instance AppType (:~>) where type App k1 (:~>) k2 (f :: k1 ~> k2) x = f @@ x infixr 0 -?> type (-?>) (k1 :: Type) (k2 :: Type) (arr :: FunArrow) = Fun k1 arr k2 listElim :: forall (a :: Type) (p :: [a] -> Type) (l :: [a]). Sing l -> p '[] -> (forall (x :: a) (xs :: [a]). Sing x -> Sing xs -> p xs -> p (x:xs)) -> p l listElim = listElimPoly @(:->) @a @p @l listElimTyFun :: forall (a :: Type) (p :: [a] ~> Type) (l :: [a]). Sing l -> p @@ '[] -> (forall (x :: a) (xs :: [a]). Sing x -> Sing xs -> p @@ xs -> p @@ (x:xs)) -> p @@ l -- The line below causes a GHC panic. It should not typecheck; -- uncomment the line below it for the correct version listElimTyFun = listElimPoly @(:->) @a @p @l -- listElimTyFun = listElimPoly @(:~>) @a @p @l listElimPoly :: forall (arr :: FunArrow) (a :: Type) (p :: ([a] -?> Type) arr) (l :: [a]). FunApp arr => Sing l -> App [a] arr Type p '[] -> (forall (x :: a) (xs :: [a]). Sing x -> Sing xs -> App [a] arr Type p xs -> App [a] arr Type p (x:xs)) -> App [a] arr Type p l listElimPoly SNil pNil _ = pNil listElimPoly (SCons x (xs :: Sing xs)) pNil pCons = pCons x xs (listElimPoly @arr @a @p @xs xs pNil pCons) }}} {{{ $ /opt/ghc/8.2.1/bin/ghci Eliminator.hs GHCi, version 8.2.0.20170623: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Eliminator ( Eliminator.hs, interpreted ) Eliminator.hs:72:17: error:ghc: panic! (the 'impossible' happened) (GHC version 8.2.0.20170623 for x86_64-unknown-linux): No skolem info: k2_a5cr Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable pprPanic, called at compiler/typecheck/TcErrors.hs:2653:5 in ghc:TcErrors Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13877> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14049: relax -Wmissing-import-lists to allow one module without implicit imports when using NoImplicitPrelude
by GHC 28 Jul '17

28 Jul '17

#14049: relax -Wmissing-import-lists to allow one module without implicit imports when using NoImplicitPrelude -------------------------------------+------------------------------------- Reporter: cdepillabout | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 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: -------------------------------------+------------------------------------- It would be nice to modify the `-Wmissing-import-lists` warning flag to allow one module with implicit imports when using the `NoImplicitPrelude` pragma. For example, imagine the following program: {{{#!hs {-# LANGUAGE NoImplicitPrelude #-} module Main where import MyCustomPrelude import Control.Monad.Trans.Reader (Reader, runReader) what :: Reader Int String -> String what x = runReader x 3 main :: IO () main = print "hello" }}} If this program is compiled with the `-Wmissing-import-lists` flag, the following warning will be produced: {{{ example.hs:5:1: warning: [-Wmissing-import-lists] The module ‘MyCustomPrelude’ does not have an explicit import list }}} I think it would be nice if this warning did not appear. Ideally, when using `NoImplicitPrelude` and `-Wmissing-import-lists` together, I would want one import per module to be permitted not to be explicit. This would make it possible to use an alternative Prelude and `-Wmissing-import-lists` at the same time. Alternatively, a new warning flag could be created with the above behavior. Maybe it could be called something like `-Wmulti-implicit- imports` or `-Wmulti-open-imports`. I would appreciate feedback/suggestions for the name. ---- PureScript currently works like I have described above. By default the `Prelude` module is not imported (so you must explicitly import it), and the compiler will warn you if you have more than one implicit import. I really like this combination and it would be nice to be able to get the same thing in Haskell. In case anyone is interested, [https://github.com/purescript/purescript/issues/1869 here] is the issue for PureScript where they talked about making this change. ---- If it seems like this is a good idea and other people are onboard, I'd be willing to implement it. I think it would be a relatively easy change, so it would be good for a first-time contributor. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14049> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5218: Add unpackCStringLen# to create Strings from string literals
by GHC 28 Jul '17

28 Jul '17

#5218: Add unpackCStringLen# to create Strings from string literals -------------------------------------+------------------------------------- Reporter: tibbe | Owner: thoughtpolice Type: feature request | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 7.0.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #5877 #10064 | Differential Rev(s): Phab:D2443 #11312 | Wiki Page: | -------------------------------------+------------------------------------- Comment (by phadej): jscholl, I'd like to participate on the proposal, bgamari mentioned above. I really think we (= community) should design this properly, as you mentioned `Addr#` and `ByteArray#` are confusing. Also Unicode/encodings add some complexity. The reward, is that we can close many tickets (at least #11312 with "single" change. I still try to wrap my head around internals, and my friends' weading is in 20 hours, so I'll return to this only next week -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5218#comment:76> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5218: Add unpackCStringLen# to create Strings from string literals
by GHC 28 Jul '17

28 Jul '17

#5218: Add unpackCStringLen# to create Strings from string literals -------------------------------------+------------------------------------- Reporter: tibbe | Owner: thoughtpolice Type: feature request | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 7.0.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #5877 #10064 | Differential Rev(s): Phab:D2443 #11312 | Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): jscholl, I was speaking to phadej yesterday and he also sounded interested in looking at this problem. Regardless of what happens, this is a change to the user-facing interface provided by the compiler and consequently falls under the [[https://github.com/ghc-proposals/ghc-proposals|GHC proposal process]]. Do you think you could write a proposal explaining your approach? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5218#comment:75> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13768: Incorrect warnings generated by exhaustiveness checker with pattern synonyms / GADT combination
by GHC 28 Jul '17

28 Jul '17

#13768: Incorrect warnings generated by exhaustiveness checker with pattern synonyms / GADT combination -------------------------------------+------------------------------------- Reporter: kosmikus | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 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: -------------------------------------+------------------------------------- The module {{{ {-# LANGUAGE DataKinds #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE PatternSynonyms #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE ViewPatterns #-} module PatSynEx where data NS (f :: k -> *) (xs :: [k]) = NS Int data IsNS (f :: k -> *) (xs :: [k]) where IsZ :: f x -> IsNS f (x ': xs) IsS :: NS f xs -> IsNS f (x ': xs) isNS :: NS f xs -> IsNS f xs isNS = undefined pattern Z :: () => (xs' ~ (x ': xs)) => f x -> NS f xs' pattern Z x <- (isNS -> IsZ x) pattern S :: () => (xs' ~ (x ': xs)) => NS f xs -> NS f xs' pattern S p <- (isNS -> IsS p) {-# COMPLETE Z, S #-} data SList :: [k] -> * where SNil :: SList '[] SCons :: SList (x ': xs) go :: SList ys -> NS f ys -> Int go SCons (Z _) = 0 go SCons (S _) = 1 go SNil _ = error "inaccessible" }}} produces the following warnings with both GHC 8.2 and 8.3: {{{ PatSynEx.hs:31:1: warning: [-Woverlapping-patterns] Pattern match has inaccessible right hand side In an equation for ‘go’: go SCons (Z _) = ... | 31 | go SCons (Z _) = 0 | ^^^^^^^^^^^^^^^^^^ PatSynEx.hs:32:1: warning: [-Woverlapping-patterns] Pattern match is redundant In an equation for ‘go’: go SCons (S _) = ... | 32 | go SCons (S _) = 1 | ^^^^^^^^^^^^^^^^^^ }}} Neither warning seems correct. The first case is not inaccessible, the second case is not redundant. The catch-all case has always been required with GHC even though it is not really reachable, but that's not the subject of this issue. I tried to simplify the issue further by getting rid of the `f` argument in `NS` and `IsNS`, but that made the issue disappear. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13768> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #2893: Implement "Quantified contexts" proposal
by GHC 28 Jul '17

28 Jul '17

#2893: Implement "Quantified contexts" proposal -------------------------------------+------------------------------------- Reporter: porges | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 6.10.1 Resolution: | Keywords: proposal Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by simonpj: Old description: > See: http://haskell.org/haskellwiki/Quantified_contexts > > Motivating example is collapsing insomeway-identical classes such as > Monoid and MonadPlus into a single class (with accompanying functions). New description: See: [wiki:QuantifiedContexts] -- -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/2893#comment:26> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12018: Equality constraint not available in pattern type signature (GADTs/ScopedTypeVariables)
by GHC 28 Jul '17

28 Jul '17

#12018: Equality constraint not available in pattern type signature (GADTs/ScopedTypeVariables) -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: lowest | Milestone: Component: Compiler | Version: 7.10.3 (Type checker) | Keywords: GADTs, | Operating System: Unknown/Multiple ScopedTypeVariables | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs data Exp a where Tru :: Ty Bool eval :: Exp a -> a eval Tru = True }}} Works fine, as does {{{#!hs eval :: Exp a -> a eval (Tru :: Exp _) = True }}} But {{{#!hs eval :: Exp a -> a eval (Tru :: Exp Bool) = True }}} doesn't, is this an intended design of GADTs/ScopedTypeVariables that the type equality constraint isn't in scope in the type signature of the pattern match, I would like to match on an existential type in my own code: {{{#!hs compile (ArrIx arr index :: Exp (Sca elt)) = do ... }}} It can be worked around by writing: {{{#!hs eval a@Tru = case a :: Exp Bool of }}} but for my own code it seems I must write {{{#!hs compile uuu@(ArrIx arr index :: Exp a) = do case uuu :: (a ~ Sca elt) => Exp (Sca elt) of }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12018> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5218: Add unpackCStringLen# to create Strings from string literals
by GHC 27 Jul '17

27 Jul '17

#5218: Add unpackCStringLen# to create Strings from string literals -------------------------------------+------------------------------------- Reporter: tibbe | Owner: thoughtpolice Type: feature request | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 7.0.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #5877 #10064 | Differential Rev(s): Phab:D2443 #11312 | Wiki Page: | -------------------------------------+------------------------------------- Comment (by jscholl): Thinking about the problem again I decided to try to add {{{ByteArray#}}} literals to GHC. The idea is the following: - Use {{{"foo"##}}} as syntax for {{{ByteArray#}}}s. This is in essence my try for a {{{String#}}} type. - Provide {{{#!haskell unpackStringLit# :: ByteArray# -> [Char] {-# INLINE[1] unpackStringLit# #-} unpackStringLit# ba# = unpackCStringWithLen# (byteArrayContents# ba#) (sizeofByteArray# ba#) }}} - Compile {{{"foo"}}} as {{{unpackStringLit# "foo"##}}} - Let rewrites fire in phase 2. - In phase 1, inline {{{unpackStringLit#}}} and let rules rewrite it to {{{unpackCStringWithLen# "foo"# 3#}}} - Thus most {{{ByteArray#}}}s should get eliminated and binary size should stay more or less the same. - If someone rewrites something like {{{ByteString.pack (unpackStringLit# lit)}}}, the literal is not eliminated and emitted to the binary. Thus a {{{ByteString}}} literal can increase binary size. However, I think this is what we want because we save making a copy of the data. - The downside is that turning optimization off causes the compiler to create a {{{ByteArray#}}} for every string literal instead of a c-string. GHCi will also allocate {{{ByteArray#}}}s instead of string literals directly. I currently implemented the new literal type, extended the parser, changed the desugaring, added the needed rules, taught GHCi to handle {{{ByteArray#}}} literals, and generated cmm Code for them. I still have to look at all parts involved for fusion and other string rules to work, check how the change affects bootstrapping with an older compiler, take a look at template haskell, and whether there are any typeable/generic things involved. I don't know how everyone feels about adding another literal type (especially because there are now two similar types, {{{Addr#}}} and {{{ByteArray#}}}, but if we want to keep binary sizes down, we need some form of {{{Addr#}}}, and it seems like having {{{ByteArray#}}} is beneficial too). Or whether it is reasonable to provide syntax for {{{ByteArray#}}}s (letting the compiler generate them would be enough for this ticket). But right now implementing it like this feels a lot better than my previous approach using unboxed tuples. And I am sorry for not saying or doing anything such a long time. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5218#comment:74> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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