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Re: [GHC] #5642: Deriving Generic of a big type takes a long time and lots of space
by GHC 17 Feb '19

17 Feb '19

#5642: Deriving Generic of a big type takes a long time and lots of space -------------------------------------+------------------------------------- Reporter: basvandijk | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.3 Resolution: | Keywords: deriving- | perf, Generics Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: T5642 Blocked By: | Blocking: Related Tickets: #13059 | Differential Rev(s): Phab:D2304 Wiki Page: | -------------------------------------+------------------------------------- Comment (by NeilMitchell): See also https://github.com/haskell/cabal/issues/5893 which hits the same issue and makes GHC itself compile slowly. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5642#comment:52> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16332: Feature request: Data.Foldable.asumMap
by GHC 16 Feb '19

16 Feb '19

#16332: Feature request: Data.Foldable.asumMap -------------------------------------+------------------------------------- Reporter: josephcsible | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: | Version: 8.6.3 libraries/base | 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'd like to request that an `asumMap` function be added to `Data.Foldable`, which would be a generalization of `concatMap` in the same way that `asum` is a generalization of `concat`. Its proposed definition: {{{#!hs asumMap :: (Foldable t, Alternative f) => (a -> f b) -> t a -> f b asumMap f = foldr ((<|>) . f) empty }}} This is almost equivalent to a combination of "asum" and "fmap", but it doesn't require a "Functor t" constraint like that does. Notes on its usefulness: * Here's a Stack Overflow question that asks for a function ((a -> Maybe b) -> [a] -> Maybe b) that this is a more general form of: https://stackoverflow.com/questions/19643664/standard-haskell- function-a-maybe-b-a-maybe-b * The alternative prelude Relude includes this function (although theirs is implemented in terms of foldMap and Alt instead of foldr and <|>): https://hackage.haskell.org/package/relude-0.4.0/docs/Relude-Foldable- Fold.html#v:asumMap * This can also be thought of as a more useful version of `Data.Foldable.find`. For example, if you have a sum type such as `Either` and want to find the value in first one of it that's `Right`, you could do `asumMap rightToMaybe x`. If you were to instead do `find isRight x`, the `Either` won't be unwrapped even though you know it's `Right`, so you'll then have to do something unclean (like a partial function) to get the value out. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16332> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14860: QuantifiedConstraints: Can't quantify constraint involving type family
by GHC 16 Feb '19

16 Feb '19

#14860: QuantifiedConstraints: Can't quantify constraint involving type family -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.5 (Type checker) | Keywords: | Operating System: Unknown/Multiple QuantifiedConstraints wipT2893 | Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This program fails to typecheck using the `wip/T2893` branch, to my surprise: {{{#!hs {-# LANGUAGE AllowAmbiguousTypes #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE QuantifiedConstraints #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE UndecidableInstances #-} module Bug where import Data.Proxy type family Apply (f :: * -> *) a type instance Apply Proxy a = Proxy a data ExTyFam f where MkExTyFam :: Apply f a -> ExTyFam f instance (forall a. Show (Apply f a)) => Show (ExTyFam f) where show (MkExTyFam x) = show x showsPrec = undefined -- Not defining these leads to the oddities observed in showList = undefined -- https://ghc.haskell.org/trac/ghc/ticket/5927#comment:32 test :: ExTyFam Proxy -> String test = show }}} This fails with: {{{ $ ghc-cq/inplace/bin/ghc-stage2 --interactive Bug.hs GHCi, version 8.5.20180128: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:17:24: error: • Could not deduce (Show (Apply f a)) arising from a use of ‘show’ from the context: forall a. Show (Apply f a) bound by the instance declaration at Bug.hs:16:10-57 • In the expression: show x In an equation for ‘show’: show (MkExTyFam x) = show x In the instance declaration for ‘Show (ExTyFam f)’ | 17 | show (MkExTyFam x) = show x | ^^^^^^ }}} I would have expected the `(forall a. Show (Apply f a))` quantified constraint to kick in, but it didn't. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14860> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16330: Type inference in presence of pattern matching on GADTs
by GHC 16 Feb '19

16 Feb '19

#16330: Type inference in presence of pattern matching on GADTs -------------------------------------+------------------------------------- Reporter: v0d1ch | Owner: (none) Type: feature | Status: new request | Priority: low | Milestone: Component: Compiler | Version: 8.6.3 Keywords: GADTs | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This small example {{{ {-# LANGUAGE GADTs #-} data G a where I :: G Integer f g = case g of I -> () }}} yields {{{ • Couldn't match expected type ‘p’ with actual type ‘()’ ‘p’ is untouchable inside the constraints: a ~ Integer bound by a pattern with constructor: I :: G Integer, in a case alternative at gadtsInference.hs:6:17 ‘p’ is a rigid type variable bound by the inferred type of f :: G a -> p at gadtsInference.hs:6:1-23 Possible fix: add a type signature for ‘f’ • In the expression: () In a case alternative: I -> () In the expression: case g of { I -> () } • Relevant bindings include f :: G a -> p (bound at gadtsInference.hs:6:1) | 6 | f g = case g of I -> () | ^^ }}} Without providing the type annotation for f `f :: G a -> ()` GHC cannot infer the correct result type. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16330> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16328: NCG: Only adjust al before foreign calls if required.
by GHC 15 Feb '19

15 Feb '19

#16328: NCG: Only adjust al before foreign calls if required. -------------------------------------+------------------------------------- Reporter: AndreasK | Owner: (none) Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 8.6.3 (CodeGen) | Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: None/Unknown (amd64) | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This is a typical sequence for a foreign call (although newCAF is a RTS function). We zero rax to indicate the number of vector registers used. However this is here (and usually) redundant. {{{ subq $8,%rsp movq %r13,%rax movq %rbx,%rsi movq %rax,%rdi xorl %eax,%eax call newCAF }}} The xor eax, eax here is redundant The System V spec says: > For calls that may call functions that use varargs or stdargs (prototype-less > calls or calls to functions containing ellipsis (...) in the declaration) %al is used > as hidden argument to specify the number of vector registers used. > The contents of %al do not need to match exactly the number of registers, but must be an upper bound on the number of vector registers used and is in the range 0–8 inclusive. This means we can omit the zeroing when we call things like RTS functions or memmov which take a fixed number of arguments at least. On windows this isn't part of the ABI at all so there we can just omit it completely. It's not a huge deal. For nofib/fannkuch-redux these xors are ~0,3% of the size of the .text segment. But it might help with cache in some edge cases. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16328> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16327: NCG: Don't double adjust SP before calls on Windows.
by GHC 15 Feb '19

15 Feb '19

#16327: NCG: Don't double adjust SP before calls on Windows. -------------------------------------+------------------------------------- Reporter: AndreasK | Owner: (none) Type: task | Status: new Priority: low | Milestone: Component: Compiler | Version: 8.6.3 (CodeGen) | Keywords: | Operating System: Windows Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Windows ABI requires callers to allocate 32 byte of space in the parameter stack space. This should be rolled into the stack adjustment for Currently we generate this code: {{{ subq $8,%rsp # for stack alignment? movq %r13,%rcx # Arg1 movq %rbx,%rdx # Arg2 subq $32,%rsp # Reserve "shadow" space + align stack if required xorl %eax,%eax # Not required for windows, even on linux only for vararg functions call newCAF addq $40,%rsp testq %rax,%rax je _c9N5 }}} Ideally this should become {{{ movq %r13,%rcx # Arg1 movq %rbx,%rdx # Arg2 subq $40,%rsp # Reserve "shadow" space xorl %eax,%eax call newCAF addq $40,%rsp testq %rax,%rax je _c9N5 }}} I haven't looked deeper into this and don't plan in the near future. But if anyone is interested I'm willing to lend a hand. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16327> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16322: "deriving newtype instance" generates an infinite loop
by GHC 15 Feb '19

15 Feb '19

#16322: "deriving newtype instance" generates an infinite loop -------------------------------------+------------------------------------- Reporter: paf31 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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: -------------------------------------+------------------------------------- I was trying to create a newtype instance for the `SqlSelect`(https://hackage.haskell.org/package/esqueleto-2.5.3/docs /Database-Esqueleto-Internal-Sql.html#t:SqlSelect) class from the `esqueleto` library. It has multiple type arguments so I was using StandaloneDeriving: {{{ newtype X a b = X { unX :: b } deriving newtype instance SqlSelect b c => SqlSelect (X a b) (X a c) }}} Unfortunately, this generates code which must include an infinite loop, because the compiled code spins, but replacing it with the obvious handwritten instance seems to fix the problem. Apologies if this has been reported or fixed elsewhere, I was unable to find any matching issues. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16322> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16306: Hadrian: First test after a full rebuild normally fails due to an additional stdout line
by GHC 15 Feb '19

15 Feb '19

#16306: Hadrian: First test after a full rebuild normally fails due to an additional stdout line -------------------------------------+------------------------------------- Reporter: RolandSenn | Owner: (none) Type: bug | Status: new Priority: low | Milestone: Component: Build System | Version: 8.6.3 (Hadrian) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- After pulling down the lates updates to my local GHC tree, I normally do the following: {{{ hadrian/build.sh clean hadrian/build.sh --flavour=devel2 -j4 hadrian/build.sh test --flavour=devel2 --freeze1 --only=T99999 }}} The first test fails with: `Actual stdout output differs from expected:` stdout contains an additonal line, obviously generated by Hadrian: {{{ +Linking /home/roland/Projekte/ghc/testsuite/mk/ghc-config ... }}} When I rerun the test, Hadrian does not re-link `ghc-config` and everything works fine! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16306> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16313: Core Lint warning (Unsafe coercion: {left, right}-hand type is levity-polymorphic)
by GHC 15 Feb '19

15 Feb '19

#16313: Core Lint warning (Unsafe coercion: {left,right}-hand type is levity- polymorphic) -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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: -------------------------------------+------------------------------------- goldfire claims [https://github.com/goldfirere/singletons/issues/383 this] is a GHC bug, so I'm reporting it here: {{{#!hs {-# LANGUAGE DataKinds #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeFamilies #-} module Bug where import Data.Kind (Type) import GHC.Exts (TYPE) import Type.Reflection (TypeRep, (:~~:)(..), eqTypeRep) import Unsafe.Coerce (unsafeCoerce) data SBool :: Bool -> Type where SFalse :: SBool False STrue :: SBool True type family DefaultEq (a :: k) (b :: k) :: Bool where DefaultEq a a = 'True DefaultEq a b = 'False sEqTypeRep :: forall rep (x :: TYPE rep) (y :: TYPE rep). TypeRep x -> TypeRep y -> SBool (DefaultEq x y) sEqTypeRep tra trb = case eqTypeRep tra trb of Just HRefl -> STrue Nothing -> unsafeCoerce SFalse }}} {{{ $ /opt/ghc/8.6.3/bin/ghc Bug.hs -O -dcore-lint -fforce-recomp [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) *** Core Lint warnings : in result of Simplifier *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Simplifier *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Simplifier *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Simplifier *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Float inwards *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Called arity analysis *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Simplifier *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Demand analysis *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Worker Wrapper binds *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Simplifier *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Exitification transformation *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Float out(FOS {Lam = Just 0, Consts = True, OverSatApps = True}) *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Common sub-expression *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Float inwards *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Simplifier *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Simplifier *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Demand analysis *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of Tidy Core *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg *** Core Lint warnings : in result of CorePrep *** <no location info>: warning: In a case alternative: (True) Unsafe coercion: left-hand type is levity-polymorphic From: x_a1rf To: y_a1rg <no location info>: warning: In a case alternative: (True) Unsafe coercion: right-hand type is levity-polymorphic From: x_a1rf To: y_a1rg }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16313> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16319: unexpected difference between newtype and data
by GHC 15 Feb '19

15 Feb '19

#16319: unexpected difference between newtype and data ----------------------------------------+--------------------------------- Reporter: pjljvdlaar | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Windows Architecture: Unknown/Multiple | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ----------------------------------------+--------------------------------- The following code compiles fine {{{#!hs -- | A referable class -- An object can only have one reference. -- For example, a function is either referenced by name of by signature but not both. class ( Eq (Ref a) , Ord (Ref a) , Hashable (Ref a) , Show (Ref a) , Read (Ref a) , Data (Ref a) ) => Referable a where type Ref a toRef :: a -> Ref a data Referable a => RefMap a = RefMap { -- | the HashMap toHashMap :: HashMap.Map (Ref a) a } deriving (Eq, Ord, Show, Read, Data) }}} yet following the hlint hint to replace data by the equivalent newtype results in the following issues: {{{ src\TorXakis\Referable.hs:59:43: error: * Could not deduce (Eq (Ref a)) arising from the 'deriving' clause of a data type declaration from the context: Eq a bound by the deriving clause for `Eq (RefMap a)' at src\TorXakis\Referable.hs:59:43-44 Possible fix: use a standalone 'deriving instance' declaration, so you can specify the instance context yourself * When deriving the instance for (Eq (RefMap a)) | 59 | } deriving (Eq, Ord, Show, Read, Data) | ^^ src\TorXakis\Referable.hs:59:47: error: * Could not deduce (Ord (Ref a)) arising from the 'deriving' clause of a data type declaration from the context: Ord a bound by the deriving clause for `Ord (RefMap a)' at src\TorXakis\Referable.hs:59:47-49 Possible fix: use a standalone 'deriving instance' declaration, so you can specify the instance context yourself * When deriving the instance for (Ord (RefMap a)) | 59 | } deriving (Eq, Ord, Show, Read, Data) }}} I assume this is a bug... -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16319> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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