June 2017 - ghc-tickets

[GHC] #12708: RFC: Representation polymorphic Num
by GHC 04 Sep '17

04 Sep '17

#12708: RFC: Representation polymorphic Num -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Core | Version: 8.0.1 Libraries | 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 can create a GHC proposal for this but I need a sanity check first {{{#!hs import Prelude hiding (Num (..)) import qualified Prelude as P import GHC.Prim import GHC.Types class Num (a :: Type k) where (+) :: a -> a -> a (-) :: a -> a -> a (*) :: a -> a -> a negate :: a -> a abs :: a -> a signum :: a -> a fromInteger :: Integer -> a instance Num Int# where (+) :: Int# -> Int# -> Int# (+) = (+#) (-) :: Int# -> Int# -> Int# (-) = (-#) (*) :: Int# -> Int# -> Int# (*) = (*#) negate :: Int# -> Int# negate = negateInt# ... fromInteger :: Integer -> Int# fromInteger (fromInteger -> I# int) = int instance Num Double# where (+) :: Double# -> Double# -> Double# (+) = (+##) (-) :: Double# -> Double# -> Double# (-) = (-##) (*) :: Double# -> Double# -> Double# (*) = (*##) negate :: Double# -> Double# negate = negateDouble# ... fromInteger :: Integer -> Double# fromInteger (fromInteger -> D# dbl) = dbl }}} Note how the `fromInteger` views aren't qualified? That's because we can branch on the kind and all of a sudden, all instances of old `Num` are instances of our `Num` {{{#!hs instance P.Num a => Num (a :: Type) where (+) = (P.+) (-) = (P.-) (*) = (P.*) negate = P.negate abs = P.abs signum = P.signum fromInteger = P.fromInteger }}} ---- Same with `Show` etc. etc. {{{#!hs class Show (a :: TYPE k) where show :: (a :: TYPE k) -> String instance P.Show a => Show (a :: Type) where show :: (a :: Type) -> String show = P.show instance Show Int# where show :: Int# -> String show int = show (I# int) instance Show Double# where show :: Double# -> String show dbl = show (D# dbl) }}} ---- What effects would this have? They are even printed the same by default {{{#!hs >>> :kind Prelude.Num Prelude.Num :: * -> Constraint >>> :kind Main.Num Main.Num :: * -> Constraint >>> :set -fprint-explicit-runtime-reps >>> :kind Main.Num Main.Num :: TYPE k -> Constraint }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12708> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13885: Template Haskell doesn't freshen GADT kind variables properly when imported from another package
by GHC 02 Sep '17

02 Sep '17

#13885: Template Haskell doesn't freshen GADT kind variables properly when imported from another package -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Template | Version: 8.0.1 Haskell | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- A simple way to illustrate this bug is with this code: {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE TypeOperators #-} module Foo where import qualified Data.Type.Equality as DTE ((:~:)) import Language.Haskell.TH data a :~: b where Refl :: a :~: a $(return []) main :: IO () main = do putStrLn "Imported\n-----" putStrLn $(reify ''(DTE.:~:) >>= stringE . pprint) putStrLn "-----\n\nLocally defined\n-----" putStrLn $(reify ''(:~:) >>= stringE . pprint) putStrLn "-----" }}} Here, I'm pretty-printing the reified Template Haskell information about two datatypes: one that is imported from another package (`base`), and another that is defined locally. Aside from their definition sites, they are otherwise identical. However, when reifying them with Template Haskell, there is another distinction one can observe: {{{ $ /opt/ghc/8.2.1/bin/runghc Foo.hs Imported ----- data Data.Type.Equality.:~: (a_0 :: k_1) (b_2 :: k_1) where Data.Type.Equality.Refl :: forall (k_1 :: *) (a_0 :: k_1) . Data.Type.Equality.:~: a_0 a_0 ----- Locally defined ----- data Foo.:~: (a_0 :: k_1) (b_2 :: k_1) where Foo.Refl :: forall (k_3 :: *) (a_4 :: k_3) . Foo.:~: a_4 a_4 ----- }}} The locally defined information looks fine, but the one imported from `base` is suspicious. Namely, the `k_1` variable is used both in the datatype head and in the quantified variables for the constructor! To confirm this, you can print out more verbose info with `show` instead of `pprint`: {{{ Imported ----- TyConI (DataD [] Data.Type.Equality.:~: [KindedTV a_6989586621679026781 (VarT k_6989586621679026780),KindedTV b_6989586621679026782 (VarT k_6989586621679026780)] Nothing [ForallC [KindedTV k_6989586621679026780 StarT,KindedTV a_6989586621679026781 (VarT k_6989586621679026780)] [] (GadtC [Data.Type.Equality.Refl] [] (AppT (AppT (ConT Data.Type.Equality.:~:) (VarT a_6989586621679026781)) (VarT a_6989586621679026781)))] []) ----- Locally defined ----- TyConI (DataD [] Foo.:~: [KindedTV a_6989586621679016094 (VarT k_6989586621679016098),KindedTV b_6989586621679016095 (VarT k_6989586621679016098)] Nothing [ForallC [KindedTV k_6989586621679016108 StarT,KindedTV a_6989586621679016096 (VarT k_6989586621679016108)] [] (GadtC [Foo.Refl] [] (AppT (AppT (ConT Foo.:~:) (VarT a_6989586621679016096)) (VarT a_6989586621679016096)))] []) ----- }}} Sure enough, the variable `k_6989586621679026780` is used in both places. I would expect this not to happen, since the two sets of variables are scoped differently, and in practice, I have to work around this by freshening the type variables for the constructor, which is annoying. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13885> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8317: Optimize tagToEnum# at Core level
by GHC 29 Aug '17

29 Aug '17

#8317: Optimize tagToEnum# at Core level ------------------------------------+------------------------------------- Reporter: jstolarek | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Compiler | 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: #6135 | ------------------------------------+------------------------------------- Old comparison primops that returned Bool were implemented by inserting call to `tagToEnum#` in the code generator. This call to `tagToEnum#` was later optimized away by a special case in the code geenrator (see [[GhcFile(compiler/codeGen/StgCmmExpr.hs)]], Note [case on bool])). Now that we have new comparison primops (see #6135) we no longer insert `tagToEnum#` in the code generator - all uses of `tagToEnum#` come from explicit calls in a source program. But we still have that special case in the code generator to optimize away `tagToEnum#`. We should drop that special case in the code generator and handle scrutinizing of `tagToEnum#` at the Core level by: 1. removing call to `tagToEnum#` in the scrutinee 2. adding calls to `dataToTag#` in case branches 3. constant-folding inserted `dataToTag#` Here is an example. This Haskell code: {{{ if tagToEnum# (a ># b) then E1 else E2 }}} will be translated to this Core: {{{ case tagToEnum# (a ># b) of True -> E1 False -> E2 }}} and optimized like this: {{{ case a ># b of dataToTag# True -> E1 dataToTag# False -> E2 }}} ====> {{{ case a ># b of 1 -> E1 0 -> E2 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8317> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13860: TODO: SMALL_MUT_ARR_PTRS in Compact.cmm
by GHC 24 Aug '17

24 Aug '17

#13860: TODO: SMALL_MUT_ARR_PTRS in Compact.cmm -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.0.1 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: -------------------------------------+------------------------------------- While looking at `Compact.cmm` I noticed that the small mutable array compaction cases are currently TODOs. Presumably this should be addressed. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13860> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13702: GHC can't produce position independent executables
by GHC 23 Aug '17

23 Aug '17

#13702: GHC can't produce position independent executables -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.0.2 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: -------------------------------------+------------------------------------- Due to #12759 we unconditionally pass `-no-pie` to GCC. However, there are legitimate reasons to want a PIE. We should have a `-fPIE` flag to match `-fPIC`, requesting that the compiler produce a position-independent executable. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13702> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13902: Misleading function arity mismatch error with TypeApplications
by GHC 22 Aug '17

22 Aug '17

#13902: Misleading function arity mismatch error with TypeApplications -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple TypeApplications | Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE TypeApplications #-} f :: a -> a f x = x g :: Int g = f @Int 42 5 }}} {{{ GHCi, version 8.3.20170614: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Main ( Bug.hs, interpreted ) Bug.hs:7:5: error: • Couldn't match expected type ‘Integer -> Int’ with actual type ‘Int’ • The function ‘f’ is applied to three arguments, but its type ‘Int -> Int’ has only one In the expression: f @Int 42 5 In an equation for ‘g’: g = f @Int 42 5 | 7 | g = f @Int 42 5 | ^^^^^^^^^^^ }}} That error message is quite confusing to read, since it reports that: * `f` is applied to three arguments, which //includes// a visible type application * `f` only has one argument, which //excludes// the visible type application We ought to be able to do better. My suggestion would be to report this instead: {{{ • The function ‘f @Int’ is applied to two arguments, but its type ‘Int -> Int’ has only one In the expression: f @Int 42 5 In an equation for ‘g’: g = f @Int 42 5 }}} Although I'm sure there are other ways the same information could be conveyed (e.g., `The function ‘f’ is applied to two value arguments`). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13902> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12874: Read/Show Incompatibility in base
by GHC 22 Aug '17

22 Aug '17

#12874: Read/Show Incompatibility in base -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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 just stumbled across a situation where the deriving machinery, in combination with types provided by base, produces Show/Read instances that are incompatible. Here is a minimal example: {{{#!hs import Data.Proxy main :: IO () main = do x <- readLn print (x :: Thing (Proxy Int)) data Thing a = Thing a deriving (Read,Show) }}} If you run this program and type "Thing Proxy" into standard in, you get a parse error. If you type in "Thing (Proxy)", it works fine. Calling `show` on `Thing Proxy` gives the string "Thing Proxy" though. So, `read . show =/= id` in this case. This might just be an issue with `Proxy`'s Read instance, but I'm not really sure. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12874> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11400: * is not an indexed type family
by GHC 21 Aug '17

21 Aug '17

#11400: * is not an indexed type family -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 (Type checker) | Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I can't seem to create an indexed data family using the kind `*` with `-XTypeInType` enabled. I have to work around it by using `Type`: {{{ $ /opt/ghc/head/bin/ghci GHCi, version 8.1.20160108: http://www.haskell.org/ghc/ :? for help λ> :set -XTypeInType -XTypeFamilies λ> import Data.Kind λ> data family IdxProxy k (a :: k) λ> data instance IdxProxy * a <interactive>:5:1: error: • Illegal family instance for ‘*’ (* is not an indexed type family) • In the data instance declaration for ‘*’ λ> data instance IdxProxy Type a λ> :kind! IdxProxy * IdxProxy * :: * -> * = IdxProxy * λ> :kind! IdxProxy Type IdxProxy Type :: Type -> * = IdxProxy Type }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11400> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13636: Enable -Wcpp-undef
by GHC 19 Aug '17

19 Aug '17

#13636: Enable -Wcpp-undef -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 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: -------------------------------------+------------------------------------- e5b3492f23c2296d0d8221e1787ee585331f726e tried (again) to enable `-Wcpp- undef` in `mk/warnings.mk`, {{{#!make SRC_HC_OPTS_STAGE1 += $(WERROR) #-Wcpp-undef SRC_HC_OPTS_STAGE2 += $(WERROR) #-Wcpp-undef }}} Unfortunately, this caused build failures in boot libraries on some platforms (e.g. `time` on Darwin). Resolve these and reenable `-Wcpp- undef`. An alternative would be to instead only add `-Wcpp-undef` to `GhcRtsHcOpts`, `GhcStage1HcOpts` and `GhcStage2HcOpts`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13636> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12155: Description of flags cut off
by GHC 19 Aug '17

19 Aug '17

#12155: Description of flags cut off -------------------------------------+------------------------------------- Reporter: mikail | Owner: Type: task | Status: new Priority: low | Milestone: Component: Documentation | Version: 8.0.1 Keywords: flags | Operating System: Unknown/Multiple Architecture: | Type of failure: Documentation Unknown/Multiple | bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The description of the flags from pages 104 to 110 are cut off in the PDF version of the User Guide. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12155> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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