January 2017 - ghc-tickets

[GHC] #11767: Add @since annotations for base instances
by GHC 26 May '18

26 May '18

#11767: Add @since annotations for base instances -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: task | Status: new Priority: normal | Milestone: 8.2.1 Component: Core | Version: 7.10.3 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: -------------------------------------+------------------------------------- Up until now we haven't been adding `@since` annotations for instances that we add to `base` (see Phab:D2051 for the discussion that spurred this ticket). We should try to get better coverage here. Unfortunately, we currently have no way to place Haddock comments on derived instances, which limits our ability consistently add these annotations. We'll need to work out some mechanism for this. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11767> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12447: Pretty-printing of equality `~` without parentheses
by GHC 26 May '18

26 May '18

#12447: Pretty-printing of equality `~` without parentheses -------------------------------------+------------------------------------- Reporter: Iceland_jack | 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: -------------------------------------+------------------------------------- Based off on [https://github.com/ekmett/constraints/blob/master/src/Data/Constraint/Defer… Data.Constraint.Deferrable] {{{#!hs {-# Language RankNTypes, ConstraintKinds #-} import Data.Typeable class Deferrable p where deferEither :: proxy p -> (p => r) -> Either String r instance (Typeable a, Typeable b) => Deferrable (a ~ b) where deferEither = undefined }}} `PolyKinds` aren't enabled so `deferEither @(_ ~ _)` is not enough to select the `Deferrable (a ~ b)` instance, but it is displayed without parentheses {{{ $ ghci -XTypeApplications -ignore-dot-ghci tyiS.hs GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( tyiS.hs, interpreted ) Ok, modules loaded: Main. *Main> :t deferEither @(_ ~ _) deferEither @(_ ~ _) :: Deferrable t ~ t1 => proxy t ~ t1 -> (t ~ t1 => r) -> Either String r }}} Instead of a preferable {{{#!hs deferEither @(_ ~ _) :: Deferrable (t ~ t1) => proxy (t ~ t1) -> (t ~ t1 => r) -> Either String r }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12447> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11540: ghc accepts non-standard type without language extension
by GHC 26 May '18

26 May '18

#11540: ghc accepts non-standard type without language extension -------------------------------------+------------------------------------- Reporter: augustss | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 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: -------------------------------------+------------------------------------- Ghc accepts this {{{ f :: Eq a => Eq b => a -> b -> Bool f a b = a==a && b==b }}} The nested contexts should require some language extension. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11540> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13192: Ambiguity Caused By PolyKind and Not Helpful Error Messages
by GHC 26 May '18

26 May '18

#13192: Ambiguity Caused By PolyKind and Not Helpful Error Messages -------------------------------------+------------------------------------- Reporter: Shayan-Najd | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following code results in a confusing/wrong error message, blaming a type variable (`a`) being a fixed Skolem variable: {{{#!hs {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE PolyKinds #-} data I a type family F x type instance F (I a) = a identity :: F (I a) -> F (I a) identity x = x }}} with the error message {{{ • Couldn't match type ‘F (I a0)’ with ‘F (I a)’ Expected type: F (I a) -> F (I a) Actual type: F (I a0) -> F (I a0) NB: ‘F’ is a type function, and may not be injective The type variable ‘a0’ is ambiguous • In the ambiguity check for ‘identity’ To defer the ambiguity check to use sites, enable AllowAmbiguousTypes In the type signature: identity :: F (I a) -> F (I a) | 9 | identity :: F (I a) -> F (I a) | ^^^^^^^^^^^^^^^^^^ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13192> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13118: let binding tuple of lenses error not an expression
by GHC 26 May '18

26 May '18

#13118: let binding tuple of lenses error not an expression -------------------------------------+------------------------------------- Reporter: codygman | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | 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: -------------------------------------+------------------------------------- This error seems to be fixed in GHC Head +/- 10 commits, but exists in GHC 8.0.1. I was told it might be a useful test case. {{{ λ> :t userId userId :: (RElem UserId rs (RIndex UserId rs), Functor f) => (Int -> f Int) -> Record rs -> f (Record rs) λ> let recLenses = userId &: Nil λ> :t recLenses recLenses :: (Functor f, RElem UserId rs (RIndex UserId rs)) => Record '[s :-> ((Int -> f Int) -> Record rs -> f (Record rs))] λ> :t recUncons recUncons :: Record (s :-> a : rs) -> (a, Record rs) λ> :t recUncons recLenses recUncons recLenses :: (Functor f, RElem UserId rs (RIndex UserId rs)) => ((Int -> f Int) -> Record rs -> f (Record rs), Record '[]) λ> let (l, ls) = recUncons recLenses <no location info>: error: not an expression: ‘let (l, ls) = recUncons recLenses’ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13118> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12854: ghc-8 prints mangled names in error message: ‘GHC.Base.$dm<$’
by GHC 26 May '18

26 May '18

#12854: ghc-8 prints mangled names in error message: ‘GHC.Base.$dm<$’ -------------------------------------+------------------------------------- Reporter: slyfox | 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: -------------------------------------+------------------------------------- Noticed on old omega codebase when built with ghc-8.0.2-rc1. Here is the minimal example: {{{#!hs {-# LANGUAGE FlexibleInstances, KindSignatures #-} {-# OPTIONS_GHC -Wall #-} data F a b instance Functor (F a) where fmap = undefined instance Functor (F String) where fmap = undefined }}} {{{ $ ghci a.hs GHCi, version 8.0.1.20161117: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/slyfox/.ghci [1 of 1] Compiling Main ( a.hs, interpreted ) a.hs:6:10: error: • Overlapping instances for Functor (F String) arising from a use of ‘GHC.Base.$dm<$’ Matching instances: instance Functor (F a) -- Defined at a.hs:5:10 instance Functor (F String) -- Defined at a.hs:6:10 • In the expression: GHC.Base.$dm<$ @F String In an equation for ‘<$’: (<$) = GHC.Base.$dm<$ @F String In the instance declaration for ‘Functor (F String)’ Failed, modules loaded: none. }}} ‘GHC.Base.$dm<$’ is an internal name. Looks like it should be a 'GHC.Base.<$'. Confusingly this does not cause overlapping error at all: {{{#!hs {-# LANGUAGE FlexibleInstances, KindSignatures #-} {-# OPTIONS_GHC -Wall #-} data F a b class C (f :: * -> *) where instance C (F a) where instance C (F String) where }}} {{{ $ ghci a.hs GHCi, version 8.0.1.20161117: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/slyfox/.ghci [1 of 1] Compiling Main ( a.hs, interpreted ) Ok, modules loaded: Main. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12854> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12794: Out of scope error not reported
by GHC 26 May '18

26 May '18

#12794: Out of scope error not reported -------------------------------------+------------------------------------- Reporter: simonpj | 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: -------------------------------------+------------------------------------- Consider {{{ {-# LANGUAGE TypeApplications #-} {-# OPTIONS -fdefer-type-errors #-} f = bar @Int }}} where `bar` is not in scope. We get {{{ T12768.hs:8:7: error: • Cannot apply expression of type ‘t1’ to a visible type argument ‘Int’ • In the expression: bar @Int }}} Confusingly, the "`bar` is not in scope`" error (the true error) has been suppressed. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12794> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12655: Bizarre parser problem: "Illegal bang-pattern" (something to do with CPP?)
by GHC 26 May '18

26 May '18

#12655: Bizarre parser problem: "Illegal bang-pattern" (something to do with CPP?) -------------------------------------+------------------------------------- Reporter: edsko | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.4.2 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: -------------------------------------+------------------------------------- This is a bug in an old ghc (7.4.2), documenting it here mostly in case anybody else comes across it. If you try to compile http://hackage.haskell.org/package/bytestring-builder-0.10.8.1.0 /bytestring-builder-0.10.8.1.0.tar.gz , ghc fails with {{{ src/Data/ByteString/Builder/Prim.hs:553:13: Illegal bang-pattern (use -XBangPatterns): ! br' }}} However, that file contains a directive {{{#!hs {-# LANGUAGE CPP, BangPatterns, ScopedTypeVariables #-} }}} at the very top of the file, so we should not be getting this error message. Now here's the bizarre thing: if we compile with `cabal --builddir=foo`, compilation happens as normal! I ran ghc with `--keep- tmp-files`, and compared the output of CPP for both variations, and literally the ''only'' difference between the two that lines {{{ # 156 "./dist/build/autogen/cabal_macros.h" }}} in one are {{{ # 156 "./foo/build/autogen/cabal_macros.h" }}} in the other. It gets weirder. I replaced the output of `src/Data/ByteString/Builder/Prim.hs` with the output of `cpp`, and removed the `CPP` language directive. If I start with the version that has `dist` (i.e., the one that results in a compilation error), ''even adding or removing a single blank line in the header of the file made the parser error go away'' (where the "header" is the bit with lines such as {{{ # 134 "./dist/build/autogen/cabal_macros.h" }}} No idea what's going on here; probably not worth investigating further. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12655> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12601: explicit foralls do not distinguish applicable types
by GHC 26 May '18

26 May '18

#12601: explicit foralls do not distinguish applicable types -------------------------------------+------------------------------------- Reporter: dmwit | 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: -------------------------------------+------------------------------------- From [https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_ext… #visible-type-application the documentation for TypeApplications]: "When printing types with -fprint-explicit-foralls enabled, type variables not available for visible type application are printed in braces. Thus, if you write myLength = length without a type signature, myLength‘s inferred type will be forall {f} {a}. Foldable f => f a -> Int." This implies that type variables that ''are'' available for type application are ''not'' printed braces (though I admit that it doesn't say so outright!). With that in mind, I find the following behavior confusing: {{{ > :set -XTypeApplications -fprint-explicit-foralls > :t (1 :: Num a => a) (1 :: Num a => a) :: forall {a}. Num a => a > (1 :: Num a => a) @Int 1 }}} The :t query seems to indicate that the type variable is not available, but the evaluation query seems to indicate that it is. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12601> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12592: Explicit type signature for type classes fails
by GHC 26 May '18

26 May '18

#12592: Explicit type signature for type classes fails -------------------------------------+------------------------------------- Reporter: Iceland_jack | 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: -------------------------------------+------------------------------------- GHC 8.0.1: Consider the [https://hackage.haskell.org/package/indexed-0.1 indexed classes]: {{{#!hs class IxFunctor f where imap :: (a -> b) -> f j k a -> f j k b class IxFunctor m => IxPointed m where ireturn :: a -> m i i a class IxPointed m => IxApplicative m where iap :: m i j (a -> b) -> m j k a -> m i k b class IxFunctor w => IxCopointed w where iextract :: w i i a -> a class IxApplicative m => IxMonad m where ibind :: (a -> m j k b) -> m i j a -> m i k b class IxMonad m => IxMonadFree f m | m -> f where iwrap :: f i j (m j k a) -> m i k a }}} GHCi gives their kinds: {{{ IxFunctor :: (k -> i -> * -> *) -> Constraint IxPointed :: (k -> k -> * -> *) -> Constraint IxApplicative :: (k -> k -> * -> *) -> Constraint IxCopointed :: (k -> k -> * -> *) -> Constraint IxMonad :: (k -> k -> * -> *) -> Constraint IxMonadFree :: (k -> k -> * -> *) -> (k -> k -> * -> *) -> Constraint }}} so I attempt to make them explicit: {{{#!hs type IxFunct i = i -> i -> Type -> Type class IxFunctor (f :: IxFunct i) where imap :: (a -> b) -> f j k a -> f j k b }}} Works fine, but if I add it to any of the others it fails: {{{#!hs -- tZRa.hs:15:17: error: … -- • Expected kind ‘i’, but ‘i’ has kind ‘*’ -- • In the first argument of ‘w’, namely ‘i’ -- In the type signature: -- iextract :: w i i a -> a -- In the class declaration for ‘IxCopointed’ -- Compilation failed. class IxFunctor w => IxCopointed (w :: IxFunct i) where iextract :: w i i a -> a -- ... class IxMonad m => IxMonadFree (f :: IxFunct i) (m :: IxFunct i) | m -> f where iwrap :: f i j (m j k a) -> m i k a }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12592> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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