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Re: [GHC] #4284: Adding parentheses introduces type error
by GHC 26 Sep '14

26 Sep '14

#4284: Adding parentheses introduces type error -------------------------------------+------------------------------------- Reporter: jpbernardy | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 6.12.3 (Type checker) | Keywords: higher-rank Resolution: fixed | polymorphism Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: GHC | Blocked By: rejects valid program | Related Tickets: Test Case: | typecheck/should_compile/T4284 | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Changes (by asr): * cc: andres.sicard.ramirez@… (removed) * cc: asr (added) * difficulty: => Unknown -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4284#comment:3> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #3304: define gcd 0 0 = 0
by GHC 26 Sep '14

26 Sep '14

#3304: define gcd 0 0 = 0 -------------------------------------+------------------------------------- Reporter: stevec | Owner: Type: proposal | Status: closed Priority: normal | Milestone: 7.2.1 Component: | Version: 7.1 libraries/base | Keywords: Resolution: fixed | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Changes (by asr): * cc: andres.sicard.ramirez@… (removed) * cc: asr, hvr, ekmett (added) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3304#comment:24> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5462: Deriving clause for arbitrary classes
by GHC 26 Sep '14

26 Sep '14

#5462: Deriving clause for arbitrary classes -------------------------------------+------------------------------------- Reporter: simonpj | Owner: dreixel Type: feature | Status: new request | Milestone: ⊥ Priority: normal | Version: 7.2.1 Component: Compiler | Keywords: Generics Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: #7346 None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by rwbarton): Well, I was imagining that you would simply reduce the constraints using whatever instances are in scope, just like when inferring the type of a top-level definition. However, now I see that this falls apart in the presence of non-uniform recursion. Quite annoying... but in this case there seems to potentially be a genuine choice involved, so it might be sensible to just reject "deriving" then and require the user to write their own instance head. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5462#comment:32> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5462: Deriving clause for arbitrary classes
by GHC 26 Sep '14

26 Sep '14

#5462: Deriving clause for arbitrary classes -------------------------------------+------------------------------------- Reporter: simonpj | Owner: dreixel Type: feature | Status: new request | Milestone: ⊥ Priority: normal | Version: 7.2.1 Component: Compiler | Keywords: Generics Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: #7346 None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by simonpj): You know what I'm going to say. Can you write a wiki page that specifies the feature, as seen by the programmer, as precisely as possible. When it is legal? What instance declaration is generated? What is the context on that instance declaration. If there are any implementation wrinkles, they can appear in a separate section on the wiki page. Thanks Simon -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5462#comment:31> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5462: Deriving clause for arbitrary classes
by GHC 26 Sep '14

26 Sep '14

#5462: Deriving clause for arbitrary classes -------------------------------------+------------------------------------- Reporter: simonpj | Owner: dreixel Type: feature | Status: new request | Milestone: ⊥ Priority: normal | Version: 7.2.1 Component: Compiler | Keywords: Generics Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: #7346 None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by dreixel): Replying to [comment:29 rwbarton]: > Can't we determine the context for the derived instance from the contexts of the default method type signatures? Not really. Look at the [http://www.haskell.org/haskellwiki/GHC.Generics serialisation example from the wiki page]: {{{ putDefault :: (Generic a, GSerialize (Rep a)) => a -> [Bit] }}} Nothing here tells us that we need `Serialize` constraints on the datatype parameters. More info comes from the K1 instance, though: {{{ instance (Serialize a) => GSerialize (K1 i a) where gput (K1 x) = put x }}} Here we see that the constructor arguments will require a `Serialize` instance. So if parameter `a` appears as argument to a constructor, we should introduce the constraint `Serialize a`. But this is non-trivial in general... the constraint might be part in an instance of the form `K1 i a :*: g`, for example. I think going for Andres's proposal is still the best idea, as it is simple and relates to something people already know. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5462#comment:30> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9634: "data X = 1": "Illegal literal in type (use DataKinds to enable): 1"
by GHC 26 Sep '14

26 Sep '14

#9634: "data X = 1": "Illegal literal in type (use DataKinds to enable): 1" -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Compiler (Type | Version: 7.9 checker) | Operating System: Keywords: | Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: Difficulty: Unknown | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- This error message is not good. "1" is not in a type position, and DataKinds will not help anything. Well, except the error message, which with DataKinds enabled is instead {{{ parse error in constructor in data/newtype declaration: 1 }}} If it's not hard, we should give that error message also when DataKinds is disabled. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9634> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9576: -fdefer-type-errors doesn't defer errors from `deriving`
by GHC 26 Sep '14

26 Sep '14

#9576: -fdefer-type-errors doesn't defer errors from `deriving` -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- When I say {{{#!hs {-# OPTIONS_GHC -fdefer-type-errors #-} data Foo = MkFoo data Bar = MkBar Foo deriving Show }}} I get a type error that there is no instance for `Show Foo`. This error should be deferred. Using standalone-deriving works just fine, though. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9576> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9612: Use functional dependencies to give more specific error messages
by GHC 26 Sep '14

26 Sep '14

#9612: Use functional dependencies to give more specific error messages -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.3 checker) | Operating System: Keywords: | Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: Difficulty: Unknown | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- An example from http://www.reddit.com/r/haskell/comments/2gryy8/stdlib_monad_error_messages…: {{{#!hs f ::(Eq a) => a -> (Int, a) -> Writer [(Int, a)] (Int, a) f y (n,x) | y == x = return (n+1, x) | otherwise = do tell (n,x) return (1,y) }}} {{{ Could not deduce (MonadWriter (Int, a) (WriterT [(Int, a)] Data.Functor.Identity.Identity)) arising from a use of ‘tell’ from the context (Eq a) bound by the type signature for f :: Eq a => a -> (Int, a) -> Writer [(Int, a)] (Int, a) at 180.hs:42:5-57 In a stmt of a 'do' block: tell (n, x) In the expression: do { tell (n, x); return (1, y) } In an equation for ‘f’: f y (n, x) | y == x = return (n + 1, x) | otherwise = do { tell (n, x); return (1, y) } }}} GHC could realize that the class `MonadWriter m w` has a functional dependency `w -> m` and notice that there is an instance `MonadWriter w (WriterT w m1)` whose `m`-part unifies with that of the needed constraint. Therefore the error cannot be a missing instance, and GHC could give a more friendly error message like {{{ Couldn't match expected type `[(Int, a)]' with actual type `(Int, a)' when unifying the instance `MonadWriter w (WriterT w m1)' with the constraint `MonadWriter (Int, a) (WriterT [(Int, a)] Identity)' arising from a use of 'tell' In a stmt of a 'do' block: tell (n, x) In the expression: ... }}} (Or, if necessary, `Could not deduce [(Int, a)] ~ (Int, a) from the context (Eq a) ...`) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9612> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9635: "Module imports form a cycle" on OS X
by GHC 26 Sep '14

26 Sep '14

#9635: "Module imports form a cycle" on OS X -------------------------------------+------------------------------------- Reporter: dalaing | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Keywords: | Operating System: MacOS X Architecture: Unknown/Multiple | Type of failure: Building Difficulty: Easy (less than 1 | GHC failed hour) | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- I ran into this while building GHC HEAD on OS X: {{{ Module imports form a cycle: module ‘Control.Applicative’ (libraries/base/Control/Applicative.hs) imports ‘Control.Arrow’ (libraries/base/Control/Arrow.hs) which imports ‘Control.Monad.Fix’ (libraries/base/Control/Monad/Fix.hs) which imports ‘System.IO’ (libraries/base/System/IO.hs) which imports ‘GHC.IO.FD’ (libraries/base/GHC/IO/FD.hs) which imports ‘GHC.Conc.IO’ (libraries/base/GHC/Conc/IO.hs) which imports ‘GHC.Event.Thread’ (libraries/base/GHC/Event/Thread.hs) which imports ‘GHC.Event.Manager’ (libraries/base/GHC/Event/Manager.hs) which imports ‘GHC.Event.KQueue’ (libraries/base/dist- install/build/GHC/Event/KQueue.hs) which imports ‘Control.Monad’ (libraries/base/Control/Monad.hs) which imports ‘Data.Traversable’ (libraries/base/Data/Traversable.hs) which imports ‘Control.Applicative’ (libraries/base/Control/Applicative.hs) make[1]: *** [libraries/base/dist-install/build/.depend-v-dyn.haskell] Error 1 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9635> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8593: vector is being built even with `--no-dph`
by GHC 26 Sep '14

26 Sep '14

#8593: vector is being built even with `--no-dph` ------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: feature request | Status: new Priority: low | Milestone: Component: Build System | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- I usually use `./sync-all --no-dph get` to speed up things a bit. But packages `vector`, `primitive` and `random` are still being pulled (by virtue of being submodules), and then built. It would be nice if the build system would build them only if `libraries/dph` is available, or have another way of making them optional. (Potentially obsolete once #8545 is done.) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8593> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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