August 2018 - ghc-tickets

[GHC] #15515: Bogus "No instance" error when type families appear in kinds
by GHC 02 Sep '18

02 Sep '18

#15515: Bogus "No instance" error when type families appear in kinds -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.4.3 (Type checker) | Keywords: TypeInType, | Operating System: Unknown/Multiple TypeFamilies | Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following code typechecks: {{{#!hs {-# LANGUAGE TypeApplications #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeInType #-} module Bug where import Data.Kind import Data.Proxy class C a where c :: Proxy a type family F data D :: F -> Type instance C (D :: F -> Type) where c = undefined }}} However, if we try to actually //use// that `C D` instance, like so: {{{#!hs c' :: Proxy (D :: F -> Type) c' = c @(D :: F -> Type) }}} Then GHC gives a rather flummoxing error message: {{{ $ /opt/ghc/8.4.3/bin/ghc Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:20:6: error: • No instance for (C D) arising from a use of ‘c’ • In the expression: c @(D :: F -> Type) In an equation for ‘c'’: c' = c @(D :: F -> Type) | 20 | c' = c @(D :: F -> Type) | ^^^^^^^^^^^^^^^^^^^ }}} But that error is clearly misleading, as we defined such a `C D` instance directly above it! The use of the type family `F` in the kind of `D` appears to play an important role in this bug. If I change `F` to be a data type (e.g., `data F`), then `c'` is accepted. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15515> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15590: Existentials in newtypes
by GHC 01 Sep '18

01 Sep '18

#15590: Existentials in newtypes -------------------------------------+------------------------------------- Reporter: NioBium | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 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: -------------------------------------+------------------------------------- Please allow existential quantification of phantom type arguments in newtypes. {{{ type role A nominal representational phantom -- Or inferred roles. newtype B a b where B :: A a b c -> B a b }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15590> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15363: Do some cleaning up of the testsuite driver
by GHC 01 Sep '18

01 Sep '18

#15363: Do some cleaning up of the testsuite driver -------------------------------------+------------------------------------- Reporter: lantti | Owner: (none) Type: task | Status: new Priority: low | Milestone: 8.6.1 Component: Test Suite | Version: 8.4.3 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: -------------------------------------+------------------------------------- When trying to understand the GHC test suite I noticed some small improvements that I could do to it. This would probably work nicely as my first task on GHC: Rewrite the timeout.hs in python, it doesn't seem to do anything that would strictly need the Haskell libraries to be used and it is the only part of the test suite driver that is not written in python. Or; See if the timeout scripts could be eliminated altogether as the python subprocess module that we are using can now (since python 3.3) handle timeouts by itself and using the timeout scripts effectively doubles the number of processes we need to create for each test case. Notice that the timeout scripts do more than just generating the timeout. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15363> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15581: Unable to commit [negative number] bytes of memory
by GHC 31 Aug '18

31 Aug '18

#15581: Unable to commit [negative number] bytes of memory -------------------------------------+------------------------------------- Reporter: nh2 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.4.3 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: -------------------------------------+------------------------------------- In issues like https://github.com/haskell/text/issues/221 we observe: {{{ "<interactive>: internal error: Unable to commit -1604321280 bytes of memory (GHC version 8.2.2 for x86_64_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} Unable to commit a **negative** amount of bytes? That looks like integer overflow somewhere. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15581> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14827: Recognize when inlining would create a join point
by GHC 31 Aug '18

31 Aug '18

#14827: Recognize when inlining would create a join point -------------------------------------+------------------------------------- Reporter: ersetzen | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: JoinPoints | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- [https://www.reddit.com/r/haskell/comments/7yh8ar/i_wrote_a_program_that_run… This discussion] revolved around a program that runs 10x faster under ghci. One way to solve this is to remove a superfluous inline pragma which allows the following transformation to happen: {{{ letrec { f a = case e of { p1 -> f a'; p2 -> (# l, r #); }} in case f e2 of { (# l, r #) -> e3; } }}} into {{{ joinrec { f a = case e of { p1 -> jump f a'; p2 -> e3; }} in jump f e2 }}} More generally a recursive let binding that is called exactly once from the outside. If all recursive calls are tail calls and the outside one isn't then we could safely replace the call with the binding and end up with join points. In this case it means a 10x speedup so it might be worth doing generally. {{{ letrec { fi = ei; } in ... (fj e) ... => ... (joinrec { fi = ei; } in fj e) ... }}} [https://gist.github.com/AndreasPK/8e6f0cbf253f0930f4cda81e685ac136 Self contained example] -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14827> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15588: Panic when abusing kind inference
by GHC 31 Aug '18

31 Aug '18

#15588: Panic when abusing kind inference -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.5 Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When I say {{{#!hs {-# LANGUAGE ScopedTypeVariables, TypeInType, TypeOperators, TypeFamilies, AllowAmbiguousTypes #-} import Data.Proxy import Data.Type.Equality import Data.Type.Bool import Data.Kind data SameKind :: forall k. k -> k -> Type type family IfK (e :: Proxy (j :: Bool)) (f :: m) (g :: n) :: If j m n where IfK (_ :: Proxy True) f _ = f IfK (_ :: Proxy False) _ g = g y :: forall ck (c :: ck). ck :~: Proxy True -> () y Refl = let x :: forall a b (d :: a). SameKind (IfK c b d) d x = undefined in () }}} HEAD says {{{ ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.7.20180827 for x86_64-apple-darwin): ASSERT failed! Bad coercion hole co_a3iZ: If j_a3j0[tau:2] m_a3j1[tau:2] a_a3gV[sk:3] a_a3gV[sk:3] nominal If j_a3j0[tau:2] m_a3j1[tau:2] a_a3jj[sk:3] ~# a_a3jj[sk:3] Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in ghc:Outputable pprPanic, called at compiler/utils/Outputable.hs:1219:5 in ghc:Outputable assertPprPanic, called at compiler/typecheck/TcMType.hs:316:25 in ghc:TcMType Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} It's as yet unclear whether the program should be accepted. My best guess is that it should, but that (even with this panic fixed) GHC isn't up to the task. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15588> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5793: make nofib awesome
by GHC 31 Aug '18

31 Aug '18

#5793: make nofib awesome -------------------------------------+------------------------------------- Reporter: dterei | Owner: michalt Type: task | Status: new Priority: normal | Milestone: ⊥ Component: NoFib benchmark | Version: suite | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: 9571 | Blocking: Related Tickets: #15357 #15333 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by sgraf): * related: #15357 => #15357 #15333 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5793#comment:36> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15565: ancient ghc release history on web page is incomplete
by GHC 30 Aug '18

30 Aug '18

#15565: ancient ghc release history on web page is incomplete -------------------------------------+------------------------------------- Reporter: j.waldmann | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.6.1 Component: Documentation | Version: 8.4.3 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: -------------------------------------+------------------------------------- (just for historical completeness) 2.10 is missing from https://downloads.haskell.org/~ghc/ . There is https://www.haskell.org/ghc/download_ghc_210.html , but the source link on that page is 404, and the wayback machine claims not to have ftp://ftp.dcs.gla.ac.uk/pub/ . Release dates are missing on https://www.haskell.org/ghc/download.html (under "Older releases"). Dates are present at https://www.haskell.org/ghc/ (under "News") but only from 6.10 onwards. I used mail archive locations mentioned at https://www.reddit.com/r/haskell/comments/6y2qbw/what_happened_to/ to find that 0.29 was announced on 29 Jul 1996. The "first full release" (0.10) was at 11 Dec 92. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15565> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15585: Testing
by GHC 30 Aug '18

30 Aug '18

#15585: Testing -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 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: -------------------------------------+------------------------------------- Hello world -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15585> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15583: Treating Constraint as Type when using (type C = Constraint)
by GHC 30 Aug '18

30 Aug '18

#15583: Treating Constraint as Type when using (type C = Constraint) -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.5 Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: #15412 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This may be similar/same as #15412? I can't get to the latest GHC right now. Again the "culprit" is using `type C = Constraint`. The code example should not compile, but the error it gives is unexpected. If we define the associated type family `Ob_ (cat :: Cat ob) :: ob -> C` using `C` {{{#!hs {-# Language KindSignatures, PolyKinds, DataKinds, TypeInType, TypeFamilies, FlexibleInstances #-} import Data.Kind type T = Type type C = Constraint type Cat ob = ob -> ob -> T class Category_ (cat :: Cat ob) where type Ob_ (cat :: Cat ob) :: ob -> C id_ :: Ob_ cat a => cat a a class NoCls (a::k) instance NoCls (a::k) instance Category_ (->) where type Ob_ (->) = NoCls -- id_ :: NoCls a => (a -> a) -XInstanceSigs id_ = () }}} the definition of `id_` fails (as we expect), but the expected type (`Ob_ (->) a -> a -> a`) is wrong: {{{#!hs $ ghci -ignore-dot-ghci 348.hs GHCi, version 8.5.20180128: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( 348.hs, interpreted ) 348.hs:22:9: error: • Couldn't match expected type ‘Ob_ (->) a -> a -> a’ with actual type ‘()’ • In the expression: () In an equation for ‘id_’: id_ = () In the instance declaration for ‘Category_ (->)’ • Relevant bindings include id_ :: Ob_ (->) a -> a -> a (bound at 348.hs:22:3) | 22 | id_ = () | ^^ Failed, no modules loaded. Prelude> }}} If we simply replace `Ob_` with `type Ob_ (cat :: Cat ob) :: ob -> Constraint`, the expected type (`a -> a`) matches my intuition: {{{ 348.hs:22:9: error: • Couldn't match expected type ‘a -> a’ with actual type ‘()’ • In the expression: () In an equation for ‘id_’: id_ = () In the instance declaration for ‘Category_ (->)’ • Relevant bindings include id_ :: a -> a (bound at 348.hs:22:3) | 22 | id_ = () | ^^ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15583> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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