April 2017 - ghc-tickets

[GHC] #13551: Support DEPRECATED and WARNING pragmas on Template Haskell
by GHC 24 Apr '17

24 Apr '17

#13551: Support DEPRECATED and WARNING pragmas on Template Haskell -------------------------------------+------------------------------------- Reporter: utdemir | Owner: (none) Type: feature | Status: new request | Priority: low | Milestone: Component: Template | Version: 8.0.1 Haskell | 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'm writing TH function from some JSON spec to Haskell data structures. Some fields are marked as deprecated in the spec, therefore I want to mark the accessors to those fields with DEPRECATED pragma, but as far as I can see, TH does not support this. I'm aware that module level DEPRECATED pragma is impossible in TH, but I still want to be able to tag top-level attributes as DEPRECATED. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13551> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13593: Unexpected behavior from Data.List.groupBy
by GHC 24 Apr '17

24 Apr '17

#13593: Unexpected behavior from Data.List.groupBy -------------------------------------+------------------------------------- Reporter: dsf | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Core | Version: 8.0.1 Libraries | 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: -------------------------------------+------------------------------------- I was hoping that {{{#!hs let notBoth1 a b = not (a == 1 && b == 1) in groupBy notBoth1 [1,1,2,3,1,1,4,5,6,1] }}} would give me {{{ [[1],[1,2,3,1],[1,4,5,6,1]] }}} but instead I get {{{ [[1],[1,2,3],[1],[1,4,5,6],[1]] }}} It seems that groupBy assumes transitivity in the argument function. I have a new implementation that does not make this assumption. Of course, the implications of changing this function's behavior are troubling. {{{#!hs groupBy' :: (a -> a -> Bool) -> [a] -> [[a]] groupBy' p (x : xs) = go [x] xs where go (x : xs) (y : zs) | p x y = go (y : x : xs) zs go g (y : zs) = reverse g : go [y] zs go g [] = [reverse g] }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13593> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5553: sendWakeup error in simple test program with MVars and killThread
by GHC 24 Apr '17

24 Apr '17

#5553: sendWakeup error in simple test program with MVars and killThread -------------------------------------+------------------------------------- Reporter: bit | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.2 Component: Runtime System | Version: 8.0.1 Resolution: | Keywords: Operating System: Linux | Architecture: x86 Type of failure: Incorrect result | Test Case: at runtime | Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * milestone: 7.4.2 => 8.2.2 Comment: We should fix this. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5553#comment:13> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5553: sendWakeup error in simple test program with MVars and killThread
by GHC 24 Apr '17

24 Apr '17

#5553: sendWakeup error in simple test program with MVars and killThread -------------------------------------+------------------------------------- Reporter: bit | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 7.4.2 Component: Runtime System | Version: 8.0.1 Resolution: | Keywords: Operating System: Linux | Architecture: x86 Type of failure: Incorrect result | Test Case: at runtime | Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Feuerbach): A few of us at nstack have been getting this error lately with ghc 8.0.2. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5553#comment:12> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11384: Error says to fix incorrect return type
by GHC 24 Apr '17

24 Apr '17

#11384: Error says to fix incorrect return type -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: GADTs | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Defining a constructor that returns the wrong type (non-parent type). If the constructor is not fully-applied or over-saturated GHC reports an error, instead of telling the developer to change the return type: {{{ Prelude> data A Prelude> data B a where MkB :: A () <interactive>:2:23: error: • Expecting one fewer argument to ‘A’ Expected kind ‘* -> *’, but ‘A’ has kind ‘*’ • In the type ‘A ()’ In the definition of data constructor ‘MkB’ In the data declaration for ‘B’ }}} Expected: 1. Suggest GADTs: {{{ • Illegal generalised algebraic data declaration for ‘B’ (Use GADTs to allow GADTs) • In the data declaration for ‘B’ }}} 2. Complain about incorrect return type: {{{ • Data constructor ‘MkB’ returns type ‘A’ instead of an instance of its parent type ‘B a’ • In the definition of data constructor ‘MkB’ In the data type declaration for ‘B’ }}} It shouldn't suggest the user fix the incorrect return type -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11384> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #1330: Impredicativity bug: Church2 test gives a rather confusing error with the HEAD
by GHC 24 Apr '17

24 Apr '17

#1330: Impredicativity bug: Church2 test gives a rather confusing error with the HEAD -------------------------------------+------------------------------------- Reporter: igloo | Owner: simonpj Type: bug | Status: new Priority: lowest | Milestone: Component: Compiler (Type | Version: 6.7 checker) | Keywords: Resolution: | TypeErrorMessages, | ImpredicativeTypes Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Church2 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * keywords: TypeErrorMessages => TypeErrorMessages, ImpredicativeTypes -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1330#comment:22> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4295: Review higher-rank and impredicative types
by GHC 24 Apr '17

24 Apr '17

#4295: Review higher-rank and impredicative types -------------------------------------+------------------------------------- Reporter: simonpj | Owner: simonpj Type: task | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 6.12.3 checker) | Keywords: Resolution: | ImpredicativeTypes Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * status: infoneeded => new -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4295#comment:30> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10709: Using ($) allows sneaky impredicativity on its left
by GHC 24 Apr '17

24 Apr '17

#10709: Using ($) allows sneaky impredicativity on its left -------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Observe the following shady interaction with GHCi: {{{ GHCi, version 7.10.1: http://www.haskell.org/ghc/ :? for help Prelude> import GHC.IO Prelude GHC.IO> import Control.Monad Prelude GHC.IO Control.Monad> :t mask mask :: forall b. ((forall a. IO a -> IO a) -> IO b) -> IO b Prelude GHC.IO Control.Monad> :t replicateM 2 . mask <interactive>:1:16: Couldn't match type ‘a’ with ‘(forall a2. IO a2 -> IO a2) -> IO a1’ ‘a’ is a rigid type variable bound by the inferred type of it :: a -> IO [a1] at Top level Expected type: a -> IO a1 Actual type: ((forall a. IO a -> IO a) -> IO a1) -> IO a1 In the second argument of ‘(.)’, namely ‘mask’ In the expression: replicateM 2 . mask Prelude GHC.IO Control.Monad> :t (replicateM 2 . mask) undefined <interactive>:1:17: Cannot instantiate unification variable ‘a0’ with a type involving foralls: (forall a1. IO a1 -> IO a1) -> IO a Perhaps you want ImpredicativeTypes In the second argument of ‘(.)’, namely ‘mask’ In the expression: replicateM 2 . mask Prelude GHC.IO Control.Monad> :t (replicateM 2 . mask) $ undefined (replicateM 2 . mask) $ undefined :: forall a. IO [a] }}} Due to the way that GHC processes `($)`, it allows this form of impredicativity on the LHS of `($)`. This case is inspired by https://github.com/ghc/nofib/blob/master/smp/threads006/Main.hs which contains the line {{{ tids <- replicateM nthreads . mask $ \_ -> forkIO $ return () }}} I think that line should be rejected. The problem stems from the treatment of `OpenKind` as described in `Note [OpenTypeKind accepts foralls]` in TcMType. Unrelated work changes this behavior by rejecting the nofib program. The point of this ticket is to provoke discussion about what is right and what is wrong here, not to request a fix. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10709> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8808: ImpredicativeTypes type checking fails depending on syntax of arguments
by GHC 24 Apr '17

24 Apr '17

#8808: ImpredicativeTypes type checking fails depending on syntax of arguments -------------------------------------+------------------------------------- Reporter: guest | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.1-rc1 checker) | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC rejects Architecture: Unknown/Multiple | valid program Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | -------------------------------------+------------------------------------- g1 and g2 below type check, but g1', g2', and g2'' don't even though the types are exactly the same. {{{ {-# LANGUAGE ImpredicativeTypes, NoMonomorphismRestriction #-} module Test where f1 :: Maybe (forall a. [a] -> [a]) -> Maybe ([Int], [Char]) f1 (Just g) = Just (g [3], g "hello") f1 Nothing = Nothing f2 :: [forall a. [a] -> [a]] -> Maybe ([Int], [Char]) f2 [g] = Just (g [3], g "hello") f2 [] = Nothing g1 = (f1 . Just) reverse g1' = f1 (Just reverse) g2 = f2 [reverse] g2' = f2 ((:[]) reverse) g2'' = f2 (reverse : []) }}} Compiling it with HEAD gives these errors: {{{ [1 of 1] Compiling Test ( test.hs, test.o ) test.hs:12:16: Couldn't match expected type ‛forall a. [a] -> [a]’ with actual type ‛[a2] -> [a2]’ In the first argument of ‛Just’, namely ‛reverse’ In the first argument of ‛f1’, namely ‛(Just reverse)’ test.hs:15:17: Couldn't match expected type ‛forall a. [a] -> [a]’ with actual type ‛[a0] -> [a0]’ In the first argument of ‛: []’, namely ‛reverse’ In the first argument of ‛f2’, namely ‛((: []) reverse)’ test.hs:16:12: Couldn't match expected type ‛forall a. [a] -> [a]’ with actual type ‛[a1] -> [a1]’ In the first argument of ‛(:)’, namely ‛reverse’ In the first argument of ‛f2’, namely ‛(reverse : [])’ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8808> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7264: Adding GHC's inferred type signatures to a working program can make it fail with Rank2Types
by GHC 24 Apr '17

24 Apr '17

#7264: Adding GHC's inferred type signatures to a working program can make it fail with Rank2Types -------------------------------------+------------------------------------- Reporter: guest | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.4.1 Resolution: fixed | Keywords: | ImpredicativeTypes Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | typecheck/should_fail/T7264 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * keywords: => ImpredicativeTypes -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7264#comment:4> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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