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[GHC] #13500: GHCi preprocesses every source file on :reload
by GHC 30 Apr '17

30 Apr '17

#13500: GHCi preprocesses every source file on :reload -------------------------------------+------------------------------------- Reporter: simonmar | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.2.1 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): Phab:D3398 | Wiki Page: -------------------------------------+------------------------------------- This is a regression in 8.0 caused by 5d48e67fac952f7188fc9ebcfbf6e3ccb9b75705 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13500> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13557: error found hole: _ is not appropriate in the following case
by GHC 30 Apr '17

30 Apr '17

#13557: error found hole: _ is not appropriate in the following case -------------------------------------+------------------------------------- Reporter: vanto | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ f :: [Char] f = [x | x <- ['a', 'b'], y <- (undefined:undefined:undefined:[]), z <- [1,2,3,4], r <- [True,False,True,False,True]] f' :: [Char] f' = [x | x <- ['a', 'b'], y <- (undefined:undefined:undefined:[]), z <- [1,2,3,4], r <- [True, False, True, False, True], s <- [_, _, _, _, _, _]] main :: IO () main = do print f print f' }}} When the code is compiled with the function {{{f}}} the result is the following:\\ {{{ "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb" }}} If we add in {{{f}}} the code {{{s <- [_, _, _, _, _, _]}}} to become the function {{{f'}}} and then compile the program, the following error is displayed.\\ {{{ test11.hs:5:131: error: * Found hole: _ :: t0 Where: `t0' is an ambiguous type variable * In the expression: _ In the expression: [_, _, _, _, ....] In a stmt of a list comprehension: s <- [_, _, _, _, ....] * Relevant bindings include r :: Bool (bound at test11.hs:5:86) z :: Integer (bound at test11.hs:5:70) y :: t1 (bound at test11.hs:5:29) x :: Char (bound at test11.hs:5:12) f' :: [Char] (bound at test11.hs:5:1) test11.hs:5:134: error: * Found hole: _ :: t0 Where: `t0' is an ambiguous type variable * In the expression: _ In the expression: [_, _, _, _, ....] In a stmt of a list comprehension: s <- [_, _, _, _, ....] * Relevant bindings include r :: Bool (bound at test11.hs:5:86) z :: Integer (bound at test11.hs:5:70) y :: t1 (bound at test11.hs:5:29) x :: Char (bound at test11.hs:5:12) f' :: [Char] (bound at test11.hs:5:1) test11.hs:5:137: error: * Found hole: _ :: t0 Where: `t0' is an ambiguous type variable * In the expression: _ In the expression: [_, _, _, _, ....] In a stmt of a list comprehension: s <- [_, _, _, _, ....] * Relevant bindings include r :: Bool (bound at test11.hs:5:86) z :: Integer (bound at test11.hs:5:70) y :: t1 (bound at test11.hs:5:29) x :: Char (bound at test11.hs:5:12) f' :: [Char] (bound at test11.hs:5:1) test11.hs:5:140: error: * Found hole: _ :: t0 Where: `t0' is an ambiguous type variable * In the expression: _ In the expression: [_, _, _, _, ....] In a stmt of a list comprehension: s <- [_, _, _, _, ....] * Relevant bindings include r :: Bool (bound at test11.hs:5:86) z :: Integer (bound at test11.hs:5:70) y :: t1 (bound at test11.hs:5:29) x :: Char (bound at test11.hs:5:12) f' :: [Char] (bound at test11.hs:5:1) test11.hs:5:143: error: * Found hole: _ :: t0 Where: `t0' is an ambiguous type variable * In the expression: _ In the expression: [_, _, _, _, ....] In a stmt of a list comprehension: s <- [_, _, _, _, ....] * Relevant bindings include r :: Bool (bound at test11.hs:5:86) z :: Integer (bound at test11.hs:5:70) y :: t1 (bound at test11.hs:5:29) x :: Char (bound at test11.hs:5:12) f' :: [Char] (bound at test11.hs:5:1) test11.hs:5:146: error: * Found hole: _ :: t0 Where: `t0' is an ambiguous type variable * In the expression: _ In the expression: [_, _, _, _, ....] In a stmt of a list comprehension: s <- [_, _, _, _, ....] * Relevant bindings include r :: Bool (bound at test11.hs:5:86) z :: Integer (bound at test11.hs:5:70) y :: t1 (bound at test11.hs:5:29) x :: Char (bound at test11.hs:5:12) f' :: [Char] (bound at test11.hs:5:1) }}} I think that here the wildcard pattern _ is justified and does not have to give this error and must be used as undefined.\\ So this error makes no sense here.\\ I propose to make a correction in this case. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13557> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13602: Pattern syntax in expression context must be clarified
by GHC 30 Apr '17

30 Apr '17

#13602: Pattern syntax in expression context must be clarified -------------------------------------+------------------------------------- Reporter: vanto | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- To simonpj\\ see tickets {{{#13557}}} and {{{#13579}}}\\ Typed Holes does not exist if we compile with GHC version 7.6.3. Instead of "error found holes" it indicates "pattern syntax in expression context: _".\\ I then understood that to improve Typed Holes it was first necessary to remove the ambiguity of the error in GHC 7.6.3 about pattern syntax in expression.\\ {{{let f = [True | x <- [_, _]]}}} raise the error {{{pattern syntax in expression context: _}}}\\ But as Typed Holes, this error has no sense here.\\ {{{let f' = [_ | x <- [1,2]]}}}will give a result like {{{"__"}}} And this calculation also makes sense if one refers to the rule of inference, as the function {{{f}}} .\\ \\ The compiler should not impose its way.\\ The programmer must be the master of his code. Here the rule of inference seems flouted.\\ Good sense or reason is argued to be the same in all people, yet differences in opinion are not due to differences in intelligence but to the fact that we use different approaches and consider different things.\\ Here you will find some ideas:\\ Instead of "underscore _" as "pattern syntax" we could use a new type called "indefinite" in expression.\\ Any calculation with "indefinite" will result in "indefinite".\\ In another calculation, the "indefinite" type could have a type defined according to a directive applied to the compiler.\\ example:\\ indefinite :: Int\\ f = [1,2,3,indefinite,5,6]\\ I took a look at ticket {{{#9497}}} and find it very interesting.\\ -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13602> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13579: -fdefer-type-errors and -fdefer-typed-holes flag do not perform their roles
by GHC 30 Apr '17

30 Apr '17

#13579: -fdefer-type-errors and -fdefer-typed-holes flag do not perform their roles -------------------------------------+------------------------------------- Reporter: vanto | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- with {{{-fdefer-type-errors}}} flag\\ Prelude > {{{let f = [True | x <- [_,_]]}}} raise two warning. Good!.\\ Prelude > {{{f}}}\\ {{{[True, True]}}}\\ With this function \\ Prelude> {{{let f' = [True | x <- [_, _]] in f'}}}\\ GHCi raise two errors. It is not clear! idem with {{{-fdefer-typed-holes}}} flag\\ If you compile, there is a warning and of course no result and after linking an error is raise. This situation is not clear for me.\\ Logically it should have a result.\\ logically the function {{{f}}} and the function {{{f'}}} send a result.\\ Typed Holes worsens in this case -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13579> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13626: Ambiguity when exporting a data constructor despite qualification
by GHC 29 Apr '17

29 Apr '17

#13626: Ambiguity when exporting a data constructor despite qualification -------------------------------------+------------------------------------- Reporter: Lemming | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 (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: -------------------------------------+------------------------------------- {{{ $ cat A.hs module A where data T = Cons $ cat B.hs module B (T(T)) where import qualified A data T = T $ ghc-8.2.0.20170422 -Wall B.hs [2 of 2] Compiling B ( B.hs, B.o ) [A changed] B.hs:1:11: error: • Ambiguous occurrence ‘T’ It could refer to either ‘A.T’, imported qualified from ‘A’ at B.hs:3:1-18 or ‘T’, defined at B.hs:5:1 • In the export: T(T) | 1 | module B (T(T)) where | ^^^^ }}} There should be no ambiguity, because there is only one data constructor named `T`. Even if `A.T`'s data constructor would also be called `T` there would be no ambiguity because `A` is imported with qualification. The problem does not appear, if `B.T`'s data constructor is named `Cons`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13626> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #3397: :step hangs when -fbreak-on-exception is set
by GHC 29 Apr '17

29 Apr '17

#3397: :step hangs when -fbreak-on-exception is set -------------------------------------+---------------------------------- Reporter: hamish | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 7.2.1 Component: GHCi | Version: 7.10.1-rc2 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: x86 Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+---------------------------------- Changes (by George): * status: new => closed * resolution: => fixed -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3397#comment:8> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #3397: :step hangs when -fbreak-on-exception is set
by GHC 29 Apr '17

29 Apr '17

#3397: :step hangs when -fbreak-on-exception is set -------------------------------------+---------------------------------- Reporter: hamish | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 7.2.1 Component: GHCi | Version: 7.10.1-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: x86 Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+---------------------------------- Comment (by George): this seems to be fixed in 8.2.1-rc1: {{{ ghci -ignore-dot-ghci bug3397.hs GHCi, version 8.2.0.20170404: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( bug3397.hs, interpreted ) [flags changed] Ok, modules loaded: Main. *Main> :set -fbreak-on-exception *Main> :steplocal main Stopped in Main.main, bug3397.hs:12:8-34 _result :: IO () = _ [bug3397.hs:12:8-34] [bug3397.hs:12:8-34] *Main> :steplocal Stopped in Main.main, bug3397.hs:12:25-33 _result :: IO () = _ -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3397#comment:7> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13468: GHC stubbornly produces dead code for empty case with type family
by GHC 28 Apr '17

28 Apr '17

#13468: GHC stubbornly produces dead code for empty case with type family -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider the following instance: {{{#!hs data Void instance Generic Void where type Rep Void = V1 from x = case x of to x = case x of }}} The pattern checker, when enabled, correctly determines that both `from` and `to` cover all cases. Yay! In order to do this, it has to reduce the `Rep Void` type family application. The optimizer, on the other hand, does not perform this reduction, presumably because it is not known to terminate. Unfortunate in this case, but fine, I suppose. Here's where it gets really unfortunate. If I write {{{#!hs to (x :: V1 r) = case x of }}} then the type checker already has to do the work of unifying `Rep Void` with `V1 r`, but the optimizer doesn't take advantage of it! With `-O2 -ddump-simpl ...`, I get {{{ -- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0} lvl_r2IT :: Addr# lvl_r2IT = "Phantom.hs:18:20-23|case"# -- RHS size: {terms: 2, types: 2, coercions: 0, joins: 0/0} $fGenericVoid1 :: Void $fGenericVoid1 = patError lvl_r2IT -- RHS size: {terms: 6, types: 7, coercions: 0, joins: 0/0} $fGenericVoid_$cto :: forall x. Rep Void x -> Void $fGenericVoid_$cto = \ (@ x_a2HT) (ds_d2J8 :: Rep Void x_a2HT) -> case ds_d2J8 of { __DEFAULT -> $fGenericVoid1 } }}} That seems rather unfortunate. The only workaround I've found so far is to actually write a function just to constrain the type: {{{#!hs absV :: V1 r -> a absV x = case x of instance Generic Void where ... to = absV }}} Finally, this is clean: {{{ -- RHS size: {terms: 5, types: 12, coercions: 0, joins: 0/0} absV :: forall r a. V1 r -> a absV = \ (@ r_a2Hy) (@ a_a2Hz) (x_a1fi :: V1 r_a2Hy) -> case x_a1fi of { } -- RHS size: {terms: 4, types: 7, coercions: 0, joins: 0/0} lvl_r2IF :: forall x. V1 x -> Void lvl_r2IF = \ (@ x_a2HP) (eta_B1 :: V1 x_a2HP) -> absV eta_B1 }}} I suppose I could add `GHC.Generics.Absurd` just to write the `absV` function for `Generic` and `Generic1` deriving, but that seems more than a little silly. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13468> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12104: Type families, `TypeError`, and `-fdefer-type-errors` cause "opt_univ fell into a hole"
by GHC 28 Apr '17

28 Apr '17

#12104: Type families, `TypeError`, and `-fdefer-type-errors` cause "opt_univ fell into a hole" -------------------------------------+------------------------------------- Reporter: antalsz | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: TypeFamilies, | Operating System: MacOS X CustomTypeErrors | Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- If I create a type family – open or closed – with a case that evaluates to a `TypeError`, and define a top-level binding with this type, loading the file with `-fdefer-type-errors` enabled (or via `:load!`/`:reload!`) panics GHC with "opt_univ fell into a hole". (And if I used `:load!` or `:reload!`, `-fdefer-type-errors` doesn't get unset.) A minimal example: {{{#!hs {-# LANGUAGE TypeFamilies, DataKinds, UndecidableInstances #-} import GHC.TypeLits type family F a where F a = TypeError (Text "error") err :: F () err = () }}} results in the panic {{{ ….hs:9:7: warning: [-Wdeferred-type-errors] • error • In the expression: () In an equation for ‘err’: err = () ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-apple-darwin): opt_univ fell into a hole {a4Va} }}} Adding more cases to the type family, or making it open, still cause the crash. This holds whether the error case is a final catch-all case, or something more like {{{#!hs type family F a where F () = TypeError (Text "error") F a = () }}} Just using a type synonym for `F` doesn't cause a panic, however, and nor does giving `err` the type `TypeError (Text "error")` directly. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12104> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13603: Can't resolve levity polymorphic superclass
by GHC 28 Apr '17

28 Apr '17

#13603: Can't resolve levity polymorphic superclass -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple LevityPolymorphism, TypeInType | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This works {{{#!hs {-# Language PolyKinds, TypeInType #-} import GHC.Exts (TYPE, RuntimeRep) class A (a :: TYPE rep) class A a => B (a :: TYPE rep) instance A b => A (a -> (b :: TYPE rep)) instance B b => B (a -> b) }}} but the moment you add (`b :: TYPE rep`) to the last line it stops working {{{#!hs -- t3I7.hs:9:10-40: error: … -- • Could not deduce (A b) -- arising from the superclasses of an instance declaration -- from the context: B b -- bound by the instance declaration at /tmp/t3I7.hs:9:10-40 -- • In the instance declaration for ‘B (a -> b)’ -- Compilation failed. {-# Language PolyKinds, TypeInType #-} import GHC.Exts (TYPE, RuntimeRep) class A (a :: TYPE rep) class A a => B (a :: TYPE rep) instance A b => A (a -> (b :: TYPE rep)) instance B b => B (a -> (b :: TYPE rep)) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13603> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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