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[GHC] #14341: Show instance for TypeReps is a bit broken
by GHC 16 Oct '18

16 Oct '18

#14341: Show instance for TypeReps is a bit broken -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Core | Version: 8.2.1 Libraries | Keywords: Typeable | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): Phab:D4084 | Wiki Page: -------------------------------------+------------------------------------- There are two problems. 1. Showing typereps of tuples can produce unnecessary parentheses: {{{ Prelude K T> typeRep @(Int, Maybe Bool) (Int,(Maybe Bool)) }}} The fix is trivial. 2. Showing typereps of ticked (i.e., lifted) tuples and lists gives hard- to-read results, because it does not use the usual special syntax: {{{ Prelude K T> typeRep @'(Int, Maybe Bool) '(,) * * Int (Maybe Bool) Prelude K T> typeRep @'[1,2,3] ': Nat 1 (': Nat 2 (': Nat 3 ('[] Nat))) }}} Fixing the lifted tuple case is trivial. Fixing the lifted list case is slightly less trivial, but not hard. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14341> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15748: panic
by GHC 15 Oct '18

15 Oct '18

#15748: panic -------------------------------------+------------------------------------- Reporter: awf | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.1 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: -------------------------------------+------------------------------------- {{{ GHCi, version 8.4.3: http://www.haskell.org/ghc/ :? for help Prelude> :print getChar >>= return ghc.exe: panic! (the 'impossible' happened) (GHC version 8.4.3 for x86_64-unknown-mingw32): isUnliftedType t1_a1tM[rt] :: TYPE t_a1tL[rt] Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler\utils\Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler\\types\\Type.hs:1939:10 in ghc:Type Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15748> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15750: Investigate haddock.base perf test
by GHC 15 Oct '18

15 Oct '18

#15750: Investigate haddock.base perf test -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: task | Status: new Priority: normal | Milestone: Component: Test Suite | Version: 8.6.1 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: -------------------------------------+------------------------------------- I've seen failures in the `haddock.base` perf test when making changes that really should have no effect on performance. My guess is that this perf test is sitting right on the line of the acceptable range. We should confirm this hunch and then update the values to recenter the range. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15750> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15725: Core Lint error: Trans coercion mis-match
by GHC 15 Oct '18

15 Oct '18

#15725: Core Lint error: Trans coercion mis-match -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.6.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: #15703 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I discovered this when debugging #15703. The following code fails to compile with `-dcore-lint`: {{{#!hs {-# LANGUAGE DefaultSignatures #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeApplications #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeInType #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE UndecidableInstances #-} module Bug where import Data.Functor.Identity (Identity(..)) import Data.Kind (Type) import GHC.Exts (Any) ----- -- The important bits ----- type instance Meth (x :: Identity a) = GenericMeth x instance SC Identity ------------------------------------------------------------------------------- data family Sing :: forall k. k -> Type data instance Sing :: forall a. Identity a -> Type where SIdentity :: Sing x -> Sing ('Identity x) newtype Par1 p = Par1 p data instance Sing :: forall p. Par1 p -> Type where SPar1 :: Sing x -> Sing ('Par1 x) type family Rep1 (f :: Type -> Type) :: Type -> Type class PGeneric1 (f :: Type -> Type) where type From1 (z :: f a) :: Rep1 f a type To1 (z :: Rep1 f a) :: f a class SGeneric1 (f :: Type -> Type) where sFrom1 :: forall (a :: Type) (z :: f a). Sing z -> Sing (From1 z) sTo1 :: forall (a :: Type) (r :: Rep1 f a). Sing r -> Sing (To1 r :: f a) type instance Rep1 Identity = Par1 instance PGeneric1 Identity where type From1 ('Identity x) = 'Par1 x type To1 ('Par1 x) = 'Identity x instance SGeneric1 Identity where sFrom1 (SIdentity x) = SPar1 x sTo1 (SPar1 x) = SIdentity x type family GenericMeth (x :: f a) :: f a where GenericMeth x = To1 (Meth (From1 x)) type family Meth (x :: f a) :: f a class SC f where sMeth :: forall a (x :: f a). Sing x -> Sing (Meth x) default sMeth :: forall a (x :: f a). ( SGeneric1 f, SC (Rep1 f) , Meth x ~ GenericMeth x ) => Sing x -> Sing (Meth x) sMeth sx = sTo1 (sMeth (sFrom1 sx)) dummy :: f a -> () dummy _ = () type instance Meth (x :: Par1 p) = x instance SC Par1 where sMeth x = x }}} {{{ $ /opt/ghc/8.6.1/bin/ghc -fforce-recomp Bug.hs -dcore-lint [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) *** Core Lint errors : in result of Simplifier *** <no location info>: warning: [in body of letrec with binders x_s1Nw :: Sing (From1 x_a1Jc)] Trans coercion mis-match: D:R:Rep1Identity[0] <a_a1Jb>_N ; Sym (Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N) Rep1 Identity a_a1Jb Par1 a_a1Jb Rep1 Identity a_a1Jb Par1 a_a1Jb *** Offending Program *** <elided> $csMeth_a1J9 [Occ=LoopBreaker] :: forall a (x :: Identity a). Sing x -> Sing (Meth x) [LclId, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=False, ConLike=False, WorkFree=False, Expandable=False, Guidance=IF_ARGS [] 100 60}] $csMeth_a1J9 = \ (@ a_a1Jb) (@ (x_a1Jc :: Identity a_a1Jb)) -> case heq_sel @ (Identity a_a1Jb) @ (Identity a_a1Jb) @ (Meth x_a1Jc) @ (GenericMeth x_a1Jc) (($d~_s1Nz @ a_a1Jb @ x_a1Jc) `cast` (((~) <Identity a_a1Jb>_N ((To1 <Identity>_N <a_a1Jb>_N (Coh (Sym (D:R:MethTYPEPar1px[0] <a_a1Jb>_N (Coh (Sym (Coh <From1 x_a1Jc>_N (D:R:Rep1Identity[0] <a_a1Jb>_N))) (D:R:Rep1Identity[0] <a_a1Jb>_N)))) (Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N) ; (Meth <*>_N (Sym (D:R:Rep1Identity[0])) <a_a1Jb>_N (Coh <From1 x_a1Jc>_N (D:R:Rep1Identity[0] <a_a1Jb>_N)))_N))_N ; (Sym (D:R:GenericMeth[0] <Identity>_N <a_a1Jb>_N <x_a1Jc>_N) ; Sym (D:R:MethTYPEIdentityax[0] <a_a1Jb>_N <x_a1Jc>_N))) ((To1 <Identity>_N <a_a1Jb>_N (Coh (Sym (Coh (Sym (Coh <From1 x_a1Jc>_N (D:R:Rep1Identity[0] <a_a1Jb>_N))) (D:R:Rep1Identity[0] <a_a1Jb>_N))) (Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N) ; (Sym (D:R:MethTYPEPar1px[0] <a_a1Jb>_N (Coh (Sym (Coh <From1 x_a1Jc>_N (D:R:Rep1Identity[0] <a_a1Jb>_N))) (D:R:Rep1Identity[0] <a_a1Jb>_N))) ; (Meth <*>_N (Sym (D:R:Rep1Identity[0])) <a_a1Jb>_N (Coh <From1 x_a1Jc>_N (D:R:Rep1Identity[0] <a_a1Jb>_N)))_N)))_N ; Sym (D:R:GenericMeth[0] <Identity>_N <a_a1Jb>_N <x_a1Jc>_N)))_R ; N:~[0] <Identity a_a1Jb>_N <Meth x_a1Jc>_N <GenericMeth x_a1Jc>_N :: (To1 (From1 x_a1Jc) ~ To1 (From1 x_a1Jc)) ~R# (Meth x_a1Jc ~~ GenericMeth x_a1Jc))) of co_a1Kd { __DEFAULT -> (\ (sx_aEZ :: Sing x_a1Jc) -> let { x_s1Nw :: Sing (From1 x_a1Jc) [LclId] x_s1Nw = $csFrom1_a1Jz @ a_a1Jb @ x_a1Jc sx_aEZ } in case x_s1Nw `cast` ((Sing (D:R:Rep1Identity[0] <a_a1Jb>_N) (Coh (Sym (Coh <From1 x_a1Jc>_N (D:R:Rep1Identity[0] <a_a1Jb>_N ; Sym (Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N)))) (Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N)))_R ; (Nth:3 (Inst (forall (x :: Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N). (Sing (Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N) (Sym (Coh <x>_N (Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N))))_R ->_R (Sing (Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N) (Sym (D:R:MethTYPEPar1px[0] <a_a1Jb>_N <x>_N) ; (Meth <*>_N (Sym (D:R:Rep1Identity[0])) <a_a1Jb>_N (Sym (Coh <x>_N (Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N))))_N))_R) (Coh <From1 x_a1Jc>_N (Sym (Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N)))) ; ((Sing (D:R:Rep1Identity[0] <a_a1Jb>_N))_R ; D:R:SingPar10[0] <a_a1Jb>_N) (Sym (Coh <Meth (From1 x_a1Jc)>_N (D:R:Rep1Identity[0] <a_a1Jb>_N)))) :: Sing (From1 x_a1Jc |> Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N) ~R# R:SingPar1 a_a1Jb (Meth (From1 x_a1Jc) |> D:R:Rep1Identity[0] <a_a1Jb>_N)) of { SPar1 @ x_a1JZ co_a1K0 x_a195 -> ($WSIdentity @ a_a1Jb @ x_a1JZ x_a195) `cast` ((Sing <Identity a_a1Jb>_N (Sym (D:R:To1IdentityaPar1[0] <a_a1Jb>_N <x_a1JZ>_N) ; (To1 <Identity>_N <a_a1Jb>_N (Sym (Coh (Sym (Coh <'Par1 x_a1JZ>_N (Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N))) (Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N)) ; (Coh <'Par1 x_a1JZ>_N (Sym (D:R:Rep1Identity[0]) <a_a1Jb>_N) ; (Sym co_a1K0 ; Coh <Meth (From1 x_a1Jc)>_N (D:R:Rep1Identity[0] <a_a1Jb>_N)))))_N))_R :: Sing ('Identity x_a1JZ) ~R# Sing (To1 (Meth (From1 x_a1Jc)))) }) `cast` (<Sing x_a1Jc>_R ->_R (Sing <Identity a_a1Jb>_N (Sym (D:R:GenericMeth[0] <Identity>_N <a_a1Jb>_N <x_a1Jc>_N) ; Sym co_a1Kd))_R :: (Sing x_a1Jc -> Sing (To1 (Meth (From1 x_a1Jc)))) ~R# (Sing x_a1Jc -> Sing (Meth x_a1Jc))) } end Rec } }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15725> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14088: Allow users to omit`forall`
by GHC 15 Oct '18

15 Oct '18

#14088: Allow users to omit`forall` -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 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: -------------------------------------+------------------------------------- Just an idea I wanted to get out there, I don't think it causes parsing ambiguity {{{#!hs -- id :: forall a. a -> a id :: a. a -> a -- everywhere :: (forall b. Term b => b -> b) -> (forall a. Term a => a -> a) everywhere :: (b. Term b => b -> b) -> (a. Term a => a -> a) }}} I think it looks beautiful but clearly more difficult to Google or grep for. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14088> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15488: GHC takes up huge amount of memory when compiling accelerate 1.2.0
by GHC 15 Oct '18

15 Oct '18

#15488: GHC takes up huge amount of memory when compiling accelerate 1.2.0 -------------------------------------+------------------------------------- Reporter: noah | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: | Operating System: Linux accelerate,memory,compile | Architecture: x86_64 | Type of failure: Compile-time (amd64) | performance bug Test Case: accelerate | Blocked By: 1.2.0 | Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Every time I try to run {{{ cabal install accelerate }}} the compiler take up nearly all 4GB of memory. Stracing it reveals that it seems to be spending nearly all of the time it runs checking a timer file descriptor, and occasionally checking its memory usage without actually doing anything about the problem. This makes installing accelerate nearly impossible. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15488> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15745: Panicking typechecker plugins
by GHC 15 Oct '18

15 Oct '18

#15745: Panicking typechecker plugins -------------------------------------+------------------------------------- Reporter: philderbeast | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 (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: -------------------------------------+------------------------------------- If I use a typechecker plugin that fails then ghc panics and I'm asked to report a bug with GHC; {{{ ghc: panic! (the 'impossible' happened) (GHC version 8.2.2 for x86_64-apple-darwin): Prelude.undefined CallStack (from HasCallStack): error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err undefined, called at plugin/Undefined/Solve/Plugin.hs:14:39 in undefined-solve- plugin-1.0.0.0-56evBabJYBHHTUlrE3HO5m:Undefined.Solve.Plugin Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} Could we please say that it is the typechecker plugin that is panicking and ask for a bug report for the faulty typechecker, giving the issues URL for the plugin if we know it? The following [https://github.com/BlockScope/undefined-plugin undefined plugins] fail for init, solve and stop functions. {{{ #!haskell module Undefined.Init.Plugin (plugin) where import Plugins (Plugin(..), tcPlugin, defaultPlugin) import TcRnTypes (TcPluginM, TcPluginResult(..), Ct, TcPlugin(..)) import GHC.TcPluginM.Extra (tracePlugin) plugin :: Plugin plugin = defaultPlugin { tcPlugin = const $ Just undefinedPlugin } undefinedPlugin :: TcPlugin undefinedPlugin = tracePlugin "undefined-init-plugin" $ TcPlugin { tcPluginInit = undefined , tcPluginSolve = \_ _ _ _ -> return $ TcPluginOk [] [] , tcPluginStop = const $ return () } }}} {{{ #!haskell module Undefined.Solve.Plugin (plugin) where import Plugins (Plugin(..), tcPlugin, defaultPlugin) import TcRnTypes (TcPluginM, TcPluginResult, Ct, TcPlugin(..)) import GHC.TcPluginM.Extra (tracePlugin) plugin :: Plugin plugin = defaultPlugin { tcPlugin = const $ Just undefinedPlugin } undefinedPlugin :: TcPlugin undefinedPlugin = tracePlugin "undefined-solve-plugin" $ TcPlugin { tcPluginInit = return () , tcPluginSolve = \_ _ _ _ -> undefined , tcPluginStop = const $ return () } }}} {{{ #!haskell module Undefined.Stop.Plugin (plugin) where import Plugins (Plugin(..), tcPlugin, defaultPlugin) import TcRnTypes (TcPluginM, TcPluginResult(..), Ct, TcPlugin(..)) import GHC.TcPluginM.Extra (tracePlugin) plugin :: Plugin plugin = defaultPlugin { tcPlugin = const $ Just undefinedPlugin } undefinedPlugin :: TcPlugin undefinedPlugin = tracePlugin "undefined-stop-plugin" $ TcPlugin { tcPluginInit = return () , tcPluginSolve = \_ _ _ _ -> return $ TcPluginOk [] [] , tcPluginStop = const $ undefined } }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15745> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15749: Long Harbormaster builds
by GHC 15 Oct '18

15 Oct '18

#15749: Long Harbormaster builds -------------------------------------+------------------------------------- Reporter: monoidal | Owner: bgamari Type: bug | Status: new Priority: normal | Milestone: Component: Continuous | Version: 8.6.1 Integration | 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: -------------------------------------+------------------------------------- Harbormaster builds sometimes take too long and are not terminated. For example, the following builds have been running for over 2 days: https://phabricator.haskell.org/harbormaster/build/54452/ https://phabricator.haskell.org/harbormaster/build/54477/ https://phabricator.haskell.org/harbormaster/build/54485/ We should have some timeout (or lower the threshold if it's already present). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15749> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4306: UNPACK can lead to unnecessary copying and wasted stack space
by GHC 15 Oct '18

15 Oct '18

#4306: UNPACK can lead to unnecessary copying and wasted stack space -------------------------------------+------------------------------------- Reporter: Olathe | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 6.12.3 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: Runtime | Test Case: performance bug | simplCore/should_compile/T4306 Blocked By: | Blocking: -------------------------------------+------------------------------------- Comment (by Krzysztof Gogolewski <krz.gogolewski@…>): In [changeset:"448b77b93b369745e9bfbc8b46a5b87bb73dd379/ghc" 448b77b9/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="448b77b93b369745e9bfbc8b46a5b87bb73dd379" Add RubbishLit for absent bindings of UnliftedRep Summary: Trac #9279 reminded us that the worker wrapper transformation copes really badly with absent unlifted boxed bindings. As `Note [Absent errors]` in WwLib.hs points out, we can't just use `absentError` for unlifted bindings because there is no bottom to hide the error in. So instead, we synthesise a new `RubbishLit` of type `forall (a :: TYPE 'UnliftedRep). a`, which code-gen may subsitute for any boxed value. We choose `()`, so that there is a good chance that the program crashes instead instead of leading to corrupt data, should absence analysis have been too optimistic (#11126). Reviewers: simonpj, hvr, goldfire, bgamari, simonmar Reviewed By: simonpj Subscribers: osa1, rwbarton, carter GHC Trac Issues: #15627, #9279, #4306, #11126 Differential Revision: https://phabricator.haskell.org/D5153 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4306#comment:3> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15746: Memory leak in print when RTS option -N is >= 2
by GHC 14 Oct '18

14 Oct '18

#15746: Memory leak in print when RTS option -N is >= 2 -------------------------------------+------------------------------------- Reporter: nmattia | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.1 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: -------------------------------------+------------------------------------- In GHC 802 the code below runs with constant memory. In GHC 822, 843 and 861 the code below runs with constant memory only if at most one core is used. If the RTS option -N is set to anything greater than 1, the memory usage grows with the size of "big_file". {{{#!hs import Data.ByteString.Builder.Extra (defaultChunkSize) import Data.Function import System.IO import qualified Data.ByteString as BS main :: IO () main = do h <- openFile "big_file" ReadMode fix $ \loop -> do bs <- BS.hGetSome h defaultChunkSize if BS.null bs then pure () else do print bs loop }}} You can reproduce this by cloning https://github.com/nmattia/ghc-print- leak and running "nix-shell". Alternatively save the code above to "Main.hs" and run "ghc ./Main.hs -threaded -rtsopts" and then "./Main +RTS -M2M -N[1|2] > /dev/null". Side note: the memory does not grow as quickly if the _size_ of the bytestring is printed, i.e. it seems to be a problem specific to hPutStrLn/print as opposed to the actual file content/bytestring being retained. I first encountered this issue when using conduit for the loop. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15746> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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