December 2015 - ghc-tickets

[GHC] #11318: Data.Text.length allocates one closure per character
by GHC 15 Apr '16

15 Apr '16

#11318: Data.Text.length allocates one closure per character -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: #11284 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In #11284 I noticed that `map Data.Text.length` applied to a list of `Text` values would result in code which would allocate one closure per character due to lack of lambda lifting. It turns out it's even worse than this. Consider this example (inspired by #11284), {{{#!hs module Hi2 (hello) where import qualified Data.Text as T hello :: Int hello = T.length hi hi :: T.Text hi = T.pack "hello" }}} When compiled with GHC 7.10.3 with `-O`, the following simplified Core is produced, {{{#!hs hello :: Int hello = case unpackCString# "hello"# of _ { Text dt_a33D dt1_a33E dt2_a33F -> let { a_a33C :: Int# a_a33C = +# dt1_a33E dt2_a33F } in letrec { $wloop_length_s3bt :: Int# -> Int# -> Int# $wloop_length_s3bt = \ (ww_s3bk :: Int#) (ww_s3bo :: Int#) -> case tagToEnum# @ Bool (>=# ww_s3bo a_a33C) of _ { False -> case indexWord16Array# dt_a33D ww_s3bo of r#_a35n { __DEFAULT -> case tagToEnum# @ Bool (geWord# r#_a35n (__word 55296)) of _ { False -> $wloop_length_s3bt (+# ww_s3bk 1) (+# ww_s3bo 1); True -> case tagToEnum# @ Bool (leWord# r#_a35n (__word 56319)) of _ { False -> $wloop_length_s3bt (+# ww_s3bk 1) (+# ww_s3bo 1); True -> $wloop_length_s3bt (+# ww_s3bk 1) (+# ww_s3bo 2) } } }; True -> ww_s3bk }; } in case $wloop_length_s3bt 0 dt1_a33E of ww_s3bs { __DEFAULT -> I# ww_s3bs } } }}} Even this simple example produces a `length` function which allocations -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11318> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10318: Cycles in class declaration (via superclasses) sometimes make sense.
by GHC 13 Apr '16

13 Apr '16

#10318: Cycles in class declaration (via superclasses) sometimes make sense. -------------------------------------+------------------------------------- Reporter: ekmett | Owner: Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.10.1 Component: Compiler | Operating System: Unknown/Multiple (Type checker) | Type of failure: GHC rejects Keywords: | valid program Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- I'd like to be able to say the following, to describe the notion of an integral domain in Haskell: {{{ -- | Product of non-zero elements always non-zero. -- Every integral domain has a field of fractions. -- The field of fractions of any field is itself. class (Frac (Frac a) ~ Frac a, Fractional (Frac a), IntegralDomain (Frac a)) => IntegralDomain a where type Frac a :: * embed :: a -> Frac a instance IntegralDomain Integer where type Frac Integer = Rational embed = fromInteger instance IntegralDomain Rational where type Frac Rational = Rational embed = id }}} But GHC gets scared when it sees the cyclic reference that `IntegralDomain` instances depend on an IntegralDomain superclass, which really is cyclic in the (Frac a) case here, and that is kind of the point. =) Right now the best approximation of the correct answer that I have for this situation is to lie and claim the constraint is weaker: {{{ -- | Product of non-zero elements always non-zero class (Frac (Frac a) ~ Frac a, Fractional (Frac a)) => AlmostIntegralDomain a where type Frac a :: * embed :: a -> Frac a class (AlmostIntegralDomain a, AlmostIntegralDomain (Frac a)) => IntegralDomain a instance (AlmostIntegralDomain a, AlmostIntegralDomain (Frac a)) => IntegralDomain a instance AlmostIntegralDomain Integer where type Frac Integer = Rational embed = fromInteger instance AlmostIntegralDomain Rational where type Frac Rational = Rational embed = id }}} Now the user is stuck defining a different class than the one they consume. Alternately, with `ConstraintKinds`, I can encode: {{{ data Dict p where Dict :: p => Dict p class (Frac (Frac a) ~ Frac a, Fractional (Frac a)) => IntegralDomain a where type Frac a :: * embed :: a -> Frac a proofFracIsIntegral :: p a -> Dict (IntegralDomain (Frac a)) default proofFracIsIntegral :: IntegralDomain (Frac a) => p a -> Dict (IntegralDomain (Frac a)) proofFracIsIntegral _ = Dict }}} but now whenever I need to get from `IntegralDomain a` to `IntegralDomain (Frac a)` I need to explicitly open the `proofFracIsIntegral` with a rats' nest of `ScopedTypeVariables`. It would be really really nice if I could get GHC to deal with this for me as I currently have a few thousand lines of code hacking around this limitation. =/ -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10318> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11213: Incorrect reported pattern synonym signature
by GHC 12 Apr '16

12 Apr '16

#11213: Incorrect reported pattern synonym signature -------------------------------------+------------------------------------- Reporter: mpickering | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Keywords: | Operating System: Unknown/Multiple PatternSynonyms | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ data T where MkT :: (Show b) => b -> T --pattern ExNumPat :: () => Show b => b -> T pattern ExNumPat x = MkT x }}} GHC reports that `ExNumPat` is missing a signature (correctly) but it reports the wrong type. The correct type is the one commented out. {{{ pstest.hs:12:1: warning: Top-level binding with no type signature: ExNumPat :: forall b. Show b => b -> T }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11213> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10001: GHC crash trying to build a project within Nix-shell
by GHC 11 Apr '16

11 Apr '16

#10001: GHC crash trying to build a project within Nix-shell -------------------------------------+------------------------------------- Reporter: wolftune | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash Test Case: | Blocked By: Blocking: | Related Tickets: 9825 Differential Revisions: | -------------------------------------+------------------------------------- {{{ <no location info>: ghc: panic! (the 'impossible' happened) (GHC version 7.8.4 for x86_64-unknown-linux): Loading temp shared object failed: /run/user/1000/ghc19915_0/ghc19915_20.so: failed to map segment from shared object Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug [20 of 99] Compiling Settings.StaticFiles ( Settings/StaticFiles.hs, dist/build/Settings/StaticFiles.o ) <no location info>: ghc: panic! (the 'impossible' happened) (GHC version 7.8.4 for x86_64-unknown-linux): Loading temp shared object failed: /run/user/1000/ghc19915_0/ghc19915_21.so: failed to map segment from shared object }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10001> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8468: ghc panic in deriving Generic1 on Array#
by GHC 07 Apr '16

07 Apr '16

#8468: ghc panic in deriving Generic1 on Array# -----------------------------------+--------------------------------------- Reporter: ghorn | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time crash Unknown/Multiple | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | -----------------------------------+--------------------------------------- Compiling the following code {{{ {-# Language DeriveGeneric, MagicHash #-} module Test where import GHC.Generics import GHC.Prim data Array a = Array (Array# a) newtype Vec a = MkVec {unVec :: Array a} deriving Generic1 }}} causes panic: {{{ [1 of 1] Compiling Test ( Test.hs, Test.o ) ghc: panic! (the 'impossible' happened) (GHC version 7.6.3 for x86_64-unknown-linux): No match in record selector tyConTyVars Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} some comments from IRC: <monoidal> with deriving Generic1 we get "Can't make a derived instance of `Generic1 Array': Array must not have unlifted or polymorphic arguments" - so it seems the check is not done recursively on used types <monoidal> * deriving Generic1 on Array -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8468> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8416: GHC.Generics needs more documentation
by GHC 07 Apr '16

07 Apr '16

#8416: GHC.Generics needs more documentation -------------------------------------+------------------------------------- Reporter: tibbe | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: libraries (other) | Version: 7.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | -------------------------------------+------------------------------------- Recently I tried to used `GHC.Generics` "in anger" for the first time, to fix some code in hashable that wasn't originally written by me. After a while I just gave up (and the generics support in hashable is now somewhat broken). The documentation for `GHC.Generics` is too incomprehensible for mere mortals. In particular, I find the documentation for `M1` and `K1` not very helpful. The documentation needs examples, more in-depth explanations of what each of the data types/constructors is used for, and finally an explanation of the up to 4 type parameters! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8416> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8797: Generics instances for monoid and applicative newtypes
by GHC 07 Apr '16

07 Apr '16

#8797: Generics instances for monoid and applicative newtypes -------------------------------------------+------------------------------- Reporter: jcristovao | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: libraries/base | Version: 7.6.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Easy (less than 1 hour) | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: -------------------------------------------+------------------------------- Hi, Is there any particular reason why there aren't Generic instances for the newtypes under Data.Monoid and Control.Applicative (for example)? I've tried adding them to GHC/Generics.hs and base compiles without problems. Could this addition be considered? Best Regards, João -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8797> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8929: Deriving Generics broken
by GHC 07 Apr '16

07 Apr '16

#8929: Deriving Generics broken ----------------------------------+------------------------------------- Reporter: guest | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: x86_64 (amd64) | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ----------------------------------+------------------------------------- I load the following code into ghci: == {-# LANGUAGE DeriveGeneric #-} import GHC.Generics import Data.Binary data Foo = Foo deriving (Show, Generic) instance Binary Foo == Then I execute: (decode . encode $ Foo) :: Foo In 7.6.3 (stage 2 booted 7.6.3), I get an error. In 7.6.3 (stage 2 booted 7.6.2), the desired result "Foo" is shown. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8929> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9523: Typo in GHC Generics documentation
by GHC 07 Apr '16

07 Apr '16

#9523: Typo in GHC Generics documentation -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.8.4 Component: Documentation | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Easy (less than 1 | Type of failure: hour) | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- In `GHC.Generics`: The types `S`, `C` and `R` are once again type-level proxies, just used to create several variants of `M1`. The `R`, it seems, is supposed to be a `D`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9523> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9527: Add Generic instances for Language.Haskell.TH
by GHC 07 Apr '16

07 Apr '16

#9527: Add Generic instances for Language.Haskell.TH -------------------------------------+------------------------------------- Reporter: nh2 | Owner: Type: feature request | Status: new Priority: normal | Milestone: 7.10.1 Component: libraries/base | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Moderate (less | Type of failure: than a day) | None/Unknown Blocked By: 9526 | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Template Haskell has a number of huge data types that would be much easier to work with if they had `Generic` instances. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9527> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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