October 2016 - ghc-tickets

[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] #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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[GHC] #11766: Lazy application gives "No instance" error while strict application works
by GHC 26 May '18

26 May '18

#11766: Lazy application gives "No instance" error while strict application works -------------------------------------+------------------------------------- Reporter: MichaelK | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1-rc2 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 might make sense if there were any IO. Here's the code: {{{#!hs {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE FunctionalDependencies #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE OverlappingInstances #-} {-# LANGUAGE UndecidableInstances #-} import Data.Maybe (isJust) data Wrapper a = Wrapper a deriving (Show) class Resolution a instance Resolution (Wrapper a) class (Resolution b, Resolution d) => C a b c d | a -> b, c -> d, a d -> c, b c -> a where cfun :: (b -> d) -> a -> c instance (Resolution b, Resolution d, a ~ b, c ~ d) => C a b c d where cfun = ($) instance (Eq a, C b c d e) => C (Maybe a -> b) c (Maybe a -> d) e where cfun f b = \x -> cfun f (b x) foo :: Maybe a -> Wrapper Bool foo = Wrapper . isJust }}} Applying `Nothing` strictly or in a `let` clause gives the expected answer (I expect that `cfun id foo` would be equivalent to `foo`): {{{#!hs *Main> cfun id foo $! Nothing Wrapper False *Main> let f = cfun id foo in f Nothing Wrapper False }}} But regular application (or just `(cfun id foo) Nothing`) returns the following error: {{{#!hs *Main> cfun id foo $ Nothing <interactive>:6:1: No instance for (Resolution (Maybe a0 -> Wrapper Bool)) (maybe you haven't applied enough arguments to a function?) arising from a use of ‘cfun’ In the expression: cfun id foo In the expression: cfun id foo $ Nothing In an equation for ‘it’: it = cfun id foo $ Nothing }}} In case it helps, the purpose of this code is for `cfun` to have the effective type of {{{#!hs cfun :: (Eq a0, Eq a1, .., Eq an) => (Wrapped b -> Wrapped c) -> (Maybe a0 -> Maybe a1 -> .. -> Maybe an -> Wrapped b) -> (Maybe a0 -> Maybe a1 -> .. -> Maybe an -> Wrapped c) }}} i.e. apply a function to the "wrapped" return value of another function of the above form. Tested on GHC 8.0.1-rc2 (most recent OSX binary as of now) and 7.10.3. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11766> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12514: Can't write unboxed sum type constructors in prefix form
by GHC 26 May '18

26 May '18

#12514: Can't write unboxed sum type constructors in prefix form -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 (Parser) | 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: -------------------------------------+------------------------------------- You can write `(# Int | Char #)`, but not `(# | #) Int Char`. This is annoying since it prevents you from partially applying unboxed sum type constructors, and it also precludes you from doing cool things like `reify ''(#||#)` (as I woefully noted [https://phabricator.haskell.org/D2448 here]). Luckily, I don't think fixing this would be too hard. The special case of parsing unboxed tuple type constructors as prefix is handled [http://git.haskell.org/ghc.git/blob/0d3bf62092de83375025edca6f7242812338542… here], so I //think// we'd just need to add a similar case for unboxed sums. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12514> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12451: TemplateHaskell and Data.Typeable - tcIfaceGlobal (local): not found
by GHC 26 May '18

26 May '18

#12451: TemplateHaskell and Data.Typeable - tcIfaceGlobal (local): not found -------------------------------------+------------------------------------- Reporter: mkloczko | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple TemplateHaskell, Typeable | Architecture: x86_64 | Type of failure: GHC rejects (amd64) | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following code produces an ghc panic error: {{{#!hs {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE ScopedTypeVariables #-} module TH where import Language.Haskell.TH import Language.Haskell.TH.Syntax import Data.Typeable usingType :: forall a. Typeable a => a -> Q [Dec] usingType _ = do -- Try to get anything using typeRep. let name = (tyConName $ typeRepTyCon $ typeRep (Proxy :: Proxy a)) `seq` "The name!" -- theF = "The name!" return [FunD (mkName "theF") [Clause [] (NormalB $ LitE $ StringL name ) []]] }}} {{{#!hs {-# LANGUAGE TemplateHaskell #-} module Main where import TH data A = A Int -- Changing the argument to (A 3) does not help. $(usingType (undefined :: A)) main = putStrLn $ theF }}} The error: {{{ ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-unknown-linux): tcIfaceGlobal (local): not found: $tcA [r5m0 :-> Type constructor ‘A’, r5m3 :-> Data constructor ‘A’, r5m9 :-> Identifier ‘A’] }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12451> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12452: TemplateHaskell - variables in top level splices and loading modules.
by GHC 26 May '18

26 May '18

#12452: TemplateHaskell - variables in top level splices and loading modules. -------------------------------------+------------------------------------- Reporter: mkloczko | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Linux TemplateHaskell | Architecture: x86_64 | Type of failure: GHC rejects (amd64) | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following code fails when loading Main module: {{{#!hs {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE ScopedTypeVariables #-} module TH where import Language.Haskell.TH import Language.Haskell.TH.Syntax import Data.Typeable usingType :: a -> Q [Dec] usingType _ = do let name = "The name!" -- theF = "The name!" return [FunD (mkName "theF") [Clause [] (NormalB $ LitE $ StringL name ) []]] }}} {{{#!hs {-# LANGUAGE TemplateHaskell #-} module Main where import TH data A = A Int -- Runs with `usingType (undefined :: A)` instead $(usingType (A 3) ) main = putStrLn $ theF }}} The error: {{{ $ ghc --make Main.hs [1 of 2] Compiling TH ( TH.hs, TH.o ) [2 of 2] Compiling Main ( Main.hs, Main.o ) attempting to use module ‘Main’ (Main.hs) which is not loaded }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12452> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12093: Wrong argument count in error message with TypeApplications
by GHC 26 May '18

26 May '18

#12093: Wrong argument count in error message with TypeApplications -------------------------------------+------------------------------------- Reporter: kwf | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When I write: {{{#!hs {-# language TypeApplications #-} module Bug where wrong = id @Bool True False }}} I get the error: {{{ • Couldn't match expected type ‘Bool -> t’ with actual type ‘Bool’ • The function ‘id’ is applied to three arguments, but its type ‘Bool -> Bool’ has only one In the expression: id @Bool True False In an equation for ‘bad’: bad = id @Bool True False • Relevant bindings include bad :: t (bound at Bug.hs:8:1) }}} This seems to tell me that I ought to get rid of //two// of the arguments given to `id`, when in fact I only ought to remove //one//. In particular, the issue seems to be that GHC includes visibly applied type parameters in the count of "how many arguments is it applied to?" but does not include them in the count of "how many arguments does it have?" Suggested fix: in cases of this error with visible type application, report something akin to, "The function ‘id’ is applied to two type arguments and two value arguments, but its type has only one value argument." -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12093> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10778: GHC doesn't infer all constrains
by GHC 25 May '18

25 May '18

#10778: GHC doesn't infer all constrains -------------------------------------+------------------------------------- Reporter: danilo2 | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Hello! Let's consider following signatures: {{{ class (IndexOf a cont ~ idx, ElementByIdx idx cont ~ a, Measurable cont) => Container cont idx a class Container cont idx a => Appendable cont idx a class HasContainer a cont | a -> cont class Monad m => RefBuilder3 a m ref | a m -> ref where mkRef3 :: a -> m (ref a) }}} Now when I define following instance: {{{ instance (PtrFrom idx i, Appendable cont idx a, HasContainer g cont, Monad m) => RefBuilder3 a (GraphBuilderT g m) (Ptr i) where mkRef3 = undefined }}} I get an error: {{{ Illegal instance declaration for ‘RefBuilder3 a (GraphBuilderT g m) (Ptr i)’ The liberal coverage condition fails in class ‘RefBuilder3’ for functional dependency: ‘a m -> ref’ Reason: lhs types ‘a’, ‘GraphBuilderT g m’ do not jointly determine rhs type ‘Ptr i’ In the instance declaration for ‘RefBuilder3 a (GraphBuilderT g m) (Ptr i)’ }}} But when I add the constraint to the instance head: {{{ instance (PtrFrom idx i, Appendable cont idx a, HasContainer g cont, Monad m, IndexOf a cont ~ idx) => RefBuilder3 a (GraphBuilderT g m) (Ptr i) where mkRef3 a = fmap ptrFrom . withGraph . append $ a }}} It compiles fine. What's interesting, the constraint should be inferred by GHC, because we've got following funds here: {{{ g -> cont -- from HasContainer cont a -> idx -- from Appendable -> Container }}} Is this a GHC bug or am I missing something? If thats a bug, I will try to clean the code and make a minimal example. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10778> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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