August 2016 - ghc-tickets

[GHC] #12371: Error message, room for improvement
by GHC 25 Aug '16

25 Aug '16

#12371: Error message, room for improvement -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple TypeApplications | Architecture: | Type of failure: Incorrect Unknown/Multiple | warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ $ ghci -ignore-dot-ghci GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help Prelude> :set -XPatternSynonyms Prelude> :set -XViewPatterns Prelude> pattern Foo a <- ((\uncons -> Just (a, as) -> a) -> a) <interactive>:3:20: error: Pattern syntax in expression context: \ uncons -> Just (a, as) -> a Did you mean to enable TypeApplications? }}} Let's: {{{ Prelude> :set -XTypeApplications Prelude> pattern Foo a <- ((\uncons -> Just (a, as) -> a) -> a) <interactive>:5:20: error: Pattern syntax in expression context: \ uncons -> Just (a, as) -> a Did you mean to enable TypeApplications? Prelude> }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12371> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12513: Template Haskell boxes singleton unboxed tuples when splicing them
by GHC 25 Aug '16

25 Aug '16

#12513: Template Haskell boxes singleton unboxed tuples when splicing them -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Template | Version: 8.0.1 Haskell | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC accepts Unknown/Multiple | invalid program Test Case: | Blocked By: Blocking: | Related Tickets: #5332 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- As noticed [https://phabricator.haskell.org/D2448#71603 here], this program somehow compiles: {{{#!hs {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE UnboxedTuples #-} module Bug where import Language.Haskell.TH.Lib import Language.Haskell.TH.Ppr import Language.Haskell.TH.Syntax f :: $([t| (# Int #) |]) -> Int f x = x g :: $(unboxedTupleT 1 `appT` conT ''Int) -> Int g x = x }}} Despite the fact that `(# Int #)` and `Int` are most definitely //not// the same type! If you compile with `-ddump-splices`, you'll see what's going on: {{{ $ /opt/ghc/head/bin/ghc Bug.hs -ddump-splices [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:12:8-40: Splicing type unboxedTupleT 1 `appT` conT ''Int ======> Int Bug.hs:9:8-23: Splicing type [t| (# Int #) |] ======> In }}} It appears that the splicing machinery is turning `(# Int #)` into `Int` behind the scenes. Luckily, this should be easy to fix. Patch coming soon. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12513> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12403: Template Haskell boxes tuple types when reifying them
by GHC 25 Aug '16

25 Aug '16

#12403: Template Haskell boxes tuple types when reifying them -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.2 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: -------------------------------------+------------------------------------- Example: {{{#!hs {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE UnboxedTuples #-} module Main where import Language.Haskell.TH data T = T (# Int, Int #) $(return []) main :: IO () main = putStrLn $(reify ''T >>= stringE . pprint) }}} {{{ $ /opt/ghc/8.0.1/bin/ghc -fforce-recomp Constraints.hs [1 of 1] Compiling Main ( Constraints.hs, Constraints.o ) Linking Constraints ... $ ./Constraints data Main.T = Main.T ((,,,) GHC.Types.Int GHC.Types.Int) }}} Patch coming soon. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12403> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12072: GHC panic on type wildcard in left-hand side of data family
by GHC 25 Aug '16

25 Aug '16

#12072: GHC panic on type wildcard in left-hand side of data family -------------------------------------+------------------------------------- Reporter: andreash | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- While playing around with data families I received the following output by ghc/ghci: {{{ ghc: panic! (the 'impossible' happened) (GHC version 7.10.3 for x86_64-unknown-linux): rnHsTyKi HsWildcardTy Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} I had accidentally left a wildcard `_` on the left-hand side of a data instance definition. To reproduce enter the following code into a file and try to load that file into ghci, or try to compile it with ghc: {{{#!hs data family Bug x data instance Bug _ = Bug }}} The expected behavior would be a (non-panic) error message of some sort. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12072> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12165: Multiple pattern type signatures accepted
by GHC 25 Aug '16

25 Aug '16

#12165: Multiple pattern type signatures accepted -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple PatternSynonyms | Architecture: | Type of failure: GHC accepts Unknown/Multiple | invalid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This hogwash is accepted: {{{ pattern P :: a -> b -> Maybe (a,b) pattern P :: foo => bar => blah -> urgh pattern P x y = Just (x, y) }}} A little experimentation shows that only the first pattern signature is examined. Others are accepted and ignored. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12165> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12535: Bad error message when unidirectional pattern synonym used in bidirectional pattern synonym
by GHC 25 Aug '16

25 Aug '16

#12535: Bad error message when unidirectional pattern synonym used in bidirectional pattern synonym -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | 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: -------------------------------------+------------------------------------- If I write: {{{ {-# LANGUAGE PatternSynonyms #-} module I where pattern P2 x y <- (x, y) pattern P1 x y = P2 x y }}} I get the error: {{{ ezyang@sabre:~$ ghc-8.0 -c I.hs I.hs:5:18: error: • non-bidirectional pattern synonym ‘P2’ used in an expression • In the expression: P2 x y In an equation for ‘$bP1’: $bP1 x y = P2 x y }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12535> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #393: functions without implementations
by GHC 24 Aug '16

24 Aug '16

#393: functions without implementations -------------------------------------+------------------------------------- Reporter: c_maeder | Owner: Type: feature request | Status: new Priority: normal | Milestone: ⊥ Component: Compiler (Type | Version: None checker) | Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Iceland_jack): Probably not worth it, but fake definitions are generated for Commentary/PrimOps {{{#!hs newArray# :: Int# -> a -> State# s -> (# State# s,MutableArray# s a #) newArray# = let x = x in x sameMutableArray# :: MutableArray# s a -> MutableArray# s a -> Int# sameMutableArray# = let x = x in x nullAddr# :: Addr# nullAddr# = let x = x in x }}} If this feature is enabled the bodies could be omitted and if we make holes representation-polymorphic (#12531) it's not such a reach to allow top-level unlifted bindings as well when body is omitted: {{{#!hs newArray# :: Int# -> a -> State# s -> (# State# s,MutableArray# s a #) sameMutableArray# :: MutableArray# s a -> MutableArray# s a -> Int# nullAddr# :: NullAddr# }}} This might avoid hacky tests mentioned in `[Compiling GHC.Prim]`. ---- === Note `[Placeholder declarations]` === > We are generating fake declarations for things in [https://hackage.haskell.org/package/ghc-prim-0.4.0.0/candidate/docs/src /GHC-Prim.html GHC.Prim], just to keep GHC's renamer and typechecker happy enough for what Haddock needs. Our main plan is to say > {{{#!hs > foo :: <type> > foo = foo > }}} > We have to silence GHC's complaints about unboxed-top-level declarations with an ad-hoc fix in `TcBinds`: see Note `[Compiling GHC.Prim]` in `TcBinds`. > > > That works for all the primitive functions except `tagToEnum#`. If we generate the binding > {{{#!hs > tagToEnum# = tagToEnum# > }}} > GHC will complain about "`tagToEnum#` must appear applied to one argument". We could hack GHC to silence this complaint when compiling `GHC.Prim`, but it seems easier to generate > {{{#!hs > tagToEnum# = let x = x in x > }}} > We don't do this for *all* bindings because for ones with an unboxed RHS we would get other complaints (e.g.can't unify "`*`" with "`#`"). === Note `[Compiling GHC.Prim]` === > Module `GHC.Prim` has no source code: it is the host module for primitive, built-in functions and types. However, for Haddock-ing purposes we generate (via `utils/genprimopcode`) a fake source file `GHC/Prim.hs`, and give it to Haddock, so that it can generate documentation. It contains definitions like > {{{#!hs > nullAddr# :: NullAddr# > }}} > which would normally be rejected as a top-level unlifted binding. But we don't want to complain, because we are only "compiling" this fake mdule [sic] for documentation purposes. Hence this hacky test for `gHC_PRIM` in `checkStrictBinds`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/393#comment:35> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5927: A type-level "implies" constraint on Constraints
by GHC 24 Aug '16

24 Aug '16

#5927: A type-level "implies" constraint on Constraints -------------------------------------+------------------------------------- Reporter: illissius | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.4.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Iceland_jack): Would there be a difference between {{{#!hs data Some :: (Type -> Constraint) -> Type where Some :: c a => a -> Some c }}} and {{{#!hs data Some' :: (Type -> Constraint) -> Type where Some' :: (ctx `Implies` c, c a) => a -> Some' ctx }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5927#comment:20> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #3314: Add compilation date to +RTS --info
by GHC 23 Aug '16

23 Aug '16

#3314: Add compilation date to +RTS --info -------------------------------------+------------------------------------- Reporter: Orphi | Owner: ak3n Type: feature request | Status: closed Priority: lowest | Milestone: Component: Compiler | Version: 6.10.2 Resolution: wontfix | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by ak3n): Since there is no so much need for such feature, ticket is closed. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3314#comment:16> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #3314: Add compilation date to +RTS --info
by GHC 23 Aug '16

23 Aug '16

#3314: Add compilation date to +RTS --info -------------------------------------+------------------------------------- Reporter: Orphi | Owner: ak3n Type: feature request | Status: closed Priority: lowest | Milestone: Component: Compiler | Version: 6.10.2 Resolution: wontfix | Keywords: 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 ak3n): * status: new => closed * differential: Phab:D2460 => * resolution: => wontfix -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3314#comment:15> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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