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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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Re: [GHC] #4347: Bug in unification of polymorphic and not-yet-polymorphic type
by GHC 24 Apr '17

24 Apr '17

#4347: Bug in unification of polymorphic and not-yet-polymorphic type -------------------------------------+------------------------------------- Reporter: dolio | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 7.10.1 Component: Compiler (Type | Version: 7.1 checker) | Keywords: Resolution: wontfix | ImpredicativeTypes Operating System: Linux | Architecture: x86_64 Type of failure: GHC rejects | (amd64) valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * keywords: => ImpredicativeTypes -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4347#comment:17> 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: infoneeded 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): * keywords: => ImpredicativeTypes -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4295#comment:29> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4281: Make impredicativity work properly
by GHC 24 Apr '17

24 Apr '17

#4281: Make impredicativity work properly -------------------------------------+------------------------------------- Reporter: simonpj | Owner: simonpj Type: task | Status: new Priority: low | Milestone: Component: Compiler | Version: 6.12.3 Resolution: | Keywords: | 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): * keywords: => ImpredicativeTypes -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4281#comment:8> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10619: Order matters when type-checking
by GHC 24 Apr '17

24 Apr '17

#10619: Order matters when type-checking -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- When I say {{{ {-# LANGUAGE RankNTypes #-} module Bug where foo True = (\x -> x) :: (forall a. a -> a) -> forall b. b -> b foo False = \y -> y }}} the module compiles. But when I say {{{ {-# LANGUAGE RankNTypes #-} module Bug where foo False = \y -> y foo True = (\x -> x) :: (forall a. a -> a) -> forall b. b -> b }}} it doesn't, failing with {{{ Bug.hs:6:13: Couldn't match type ‘b0 -> b0’ with ‘forall a. a -> a’ Expected type: (forall a. a -> a) -> forall a. a -> a Actual type: (forall a. a -> a) -> b0 -> b0 In the expression: (\ x -> x) :: (forall a. a -> a) -> forall b. b -> b In an equation for ‘foo’: foo True = (\ x -> x) :: (forall a. a -> a) -> forall b. b -> b }}} I believe this behavior stems from the special case in `tcMonoBinds`, for non-recursive functions without a type signature. I believe the bug would be fixed if that function also checks to make sure that there is precisely one clause to the function. Do you agree? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10619> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13553: GHC 8.2.1 preprocesses __GLASGOW_HASKELL__ incorrectly with cpphs
by GHC 23 Apr '17

23 Apr '17

#13553: GHC 8.2.1 preprocesses __GLASGOW_HASKELL__ incorrectly with cpphs -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | 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: -------------------------------------+------------------------------------- I'm not exactly sure if this is the fault of `cpphs` or GHC, but I'll report this issue to GHC Trac for now, since (ostensibly) the only thing that has changed in this equation is the GHC version. Take this file: {{{#!hs {-# LANGUAGE CPP #-} module Bug where foo :: Int #if __GLASGOW_HASKELL__ >= 800 foo = 42 #else foo = "wrong type" #endif }}} Now let's compile it using `cpphs-1.20.4` as a preprocessor. With GHC 8.0, everything works out fine: {{{ $ /opt/ghc/8.0.2/bin/ghc Bug.hs -pgmP cpphs -optP --cpp Warning: Can't find file "/opt/ghc/8.0.2/lib/ghc-8.0.2/include/ghcversion.h" in directories Asked for by: Bug.hs at line 1 col 1 [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) }}} But with GHC 8.2.1, things go awry: {{{ $ /opt/ghc/8.2.1/bin/ghc Bug.hs -pgmP cpphs -optP --cpp Warning: Can't find file "/opt/ghc/8.2.1/lib/ghc-8.2.0.20170403/include/ghcversion.h" in directories Asked for by: Bug.hs at line 1 col 1 [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:8:7: error: • Couldn't match expected type ‘Int’ with actual type ‘[Char]’ • In the expression: "wrong type" In an equation for ‘foo’: foo = "wrong type" | 8 | foo = "wrong type" | ^^^^^^^^^^^^ }}} This bug causes several libraries on Hackage which use `cpphs` as a preprocessor to fail when built with GHC 8.2.1, including `Agda`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13553> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13605: GHC Bug when updating stack
by GHC 23 Apr '17

23 Apr '17

#13605: GHC Bug when updating stack -------------------------------------+------------------------------------- Reporter: pighcu | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 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: panic! (the 'impossible' happened) (GHC version 7.10.3 for x86_64-apple-darwin): Loading temp shared object failed: dlopen(/var/folders/y5/cc8zwjz12w1567wglxgzt05c0000gn/T/ghc39074_0/libghc_68.dylib, 5): no suitable image found. Did find: /var/folders/y5/cc8zwjz12w1567wglxgzt05c0000gn/T/ghc39074_0/libghc_68.dylib: malformed mach-o: load commands size (49368) > 32768 Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13605> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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