September 2018 - ghc-tickets

[GHC] #15399: Build failure on PowerPC 64-bit big endian
by GHC 11 Jan '19

11 Jan '19

#15399: Build failure on PowerPC 64-bit big endian ---------------------------------+---------------------------------------- Reporter: trommler | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.5 Keywords: | Operating System: Linux Architecture: powerpc64 | Type of failure: Building GHC failed Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ---------------------------------+---------------------------------------- Building GHC 8.6.1 alpha 2 fails with these errors on Powerpc 64-bit big endian Linux: {{{ [ 5076s] utils/check-ppr/Main.hs:44:18: error: [ 5076s] * GHC internal error: `astFile' is not in scope during type checking, but it passed the renamer [ 5076s] tcl_env of environment: [agVj :-> Identifier[libdir::FilePath, NotLetBound], [ 5076s] agVk :-> Identifier[fileName::String, NotLetBound], [ 5076s] agVl :-> Identifier[p::a, NotLetBound], [ 5076s] agVo :-> Identifier[anns::ApiAnns, TopLevelLet [agVl :-> p] False], [ 5076s] agVp :-> Identifier[pragmas::String, TopLevelLet [agVo :-> anns] False], [ 5076s] agVq :-> Identifier[newFile::FilePath, TopLevelLet [agVk :-> fileName] False], [ 5076s] rfRp :-> Identifier[usage::String, TopLevelLet [] True], [ 5076s] rfU1 :-> Identifier[main::IO (), TopLevelLet [] True], [ 5076s] rfU2 :-> Identifier[testOneFile::FilePath [ 5076s] -> String [ 5076s] -> IO (), TopLevelLet [] True], [ 5076s] rfU3 :-> Identifier[parseOneFile::FilePath [ 5076s] -> FilePath [ 5076s] -> IO [ 5076s] ParsedModule, TopLevelLet [] True], [ 5076s] rfU4 :-> Identifier[getPragmas::ApiAnns -> String, TopLevelLet], [ 5076s] rfU5 :-> Identifier[pp::forall a. [ 5076s] Outputable a => [ 5076s] a -> String, TopLevelLet [] True]] [ 5076s] * In the first argument of `writeFile', namely `astFile' [ 5076s] In a stmt of a 'do' block: writeFile astFile origAst [ 5076s] In the expression: [ 5076s] do p <- parseOneFile libdir fileName [ 5076s] let pped = pragmas ++ "\n" ++ pp (pm_parsed_source p) [ 5076s] anns = pm_annotations p [ 5076s] .... [ 5076s] writeFile astFile origAst [ 5076s] writeFile newFile pped [ 5076s] .... [ 5076s] | [ 5076s] 44 | writeFile astFile origAst [ 5076s] | ^^^^^^^ [ 5076s] utils/check-ppr/ghc.mk:18: recipe for target 'utils/check-ppr /dist-install/build/Main.o' failed [ 5076s] make[1]: *** [utils/check-ppr/dist-install/build/Main.o] Error 1 [ 5076s] make[1]: *** Waiting for unfinished jobs.... [ 5077s] [ 5077s] utils/check-api-annotations/Main.hs:116:32: error: [ 5077s] * GHC internal error: `GenericQ' is not in scope during type checking, but it passed the renamer [ 5077s] tcl_env of environment: [agZx :-> Type variable `r' = r :: k0] [ 5077s] * In the type signature: [ 5077s] everything :: (r -> r -> r) -> GenericQ r -> GenericQ r [ 5077s] | [ 5077s] 116 | everything :: (r -> r -> r) -> GenericQ r -> GenericQ r [ 5077s] | ^^^^^^^^ [ 5077s] utils/check-api-annotations/ghc.mk:18: recipe for target 'utils /check-api-annotations/dist-install/build/Main.o' failed [ 5077s] make[1]: *** [utils/check-api-annotations/dist- install/build/Main.o] Error 1 [ 5077s] [ 5077s] utils/ghctags/Main.hs:61:36: error: [ 5077s] * GHC internal error: `FoundThing' is not in scope during type checking, but it passed the renamer [ 5077s] tcl_env of environment: [rCTr :-> ATcTyCon FileData :: *, [ 5077s] rCTs :-> APromotionErr RecDataConPE, [ 5077s] rCTw :-> ATcTyCon FileName :: *] [ 5077s] * In the type `[FoundThing]' [ 5077s] In the definition of data constructor `FileData' [ 5077s] In the data declaration for `FileData' [ 5077s] | [ 5077s] 61 | data FileData = FileData FileName [FoundThing] (Map Int String) [ 5077s] | ^^^^^^^^^^ [ 5077s] utils/ghctags/ghc.mk:18: recipe for target 'utils/ghctags/dist- install/build/Main.o' failed }}} Alpha 2 builds fine on PowerPC 64-bit little endian Linux. I am setting version to 8.5 as there is no tag for 8.6.1 alpha 2 yet. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15399> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 11

[GHC] #15357: Make nofib suitable for runtime measurements.
by GHC 09 Jan '19

09 Jan '19

#15357: Make nofib suitable for runtime measurements. -------------------------------------+------------------------------------- Reporter: AndreasK | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.1 Component: NoFib | Version: 8.4.3 benchmark suite | 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: -------------------------------------+------------------------------------- Currently many benchmarks in a default nofib run have runtimes so low that they become meaningless. This comes with a bunch of issues: * It takes up build/runtime while not actually improving the accuracy of runtime measurements. * It skews results as the jump from 1ms to 2ms registers as a 200% change. * It can hide regression which fall outside of the measured granularity. * Higher number of runs per benchmark spend far too much time on the few slower benchmarks. At the extreme end there are 9 benchmarks with runtimes shorter than the granularity of 1ms. For some benchmarks changing this might be as easy as increasing the number of runs/iterations. For others changing problem sizes is not as easy since they process more complex input data. Below are the runtimes of a recent default nofib run. ||= benchmark =|| Time (ms) || || ansi || 0 || || awards || 0 || || banner || 0 || || calendar || 0 || || expert || 0 || || gen_regexps || 0 || || grep || 0 || || pretty || 0 || || scc || 0 || || cse || 1 || || eliza || 1 || || lift || 1 || || mkhprog || 1 || || prolog || 1 || || sorting || 1 || || veritas || 1 || || knights || 2 || || minimax || 2 || || x2n1 || 2 || || mandel2 || 3 || || parstof || 3 || || fluid || 4 || || pic || 4 || || boyer2 || 5 || || bspt || 5 || || cryptarithm2 || 5 || || fish || 6 || || gg || 6 || || reptile || 6 || || symalg || 6 || || tak || 6 || || VSD || 7 || || rfib || 7 || || queens || 9 || || rewrite || 9 || || sched || 11 || || fem || 12 || || fibheaps || 13 || || parser || 14 || || rsa || 14 || || genfft || 15 || || clausify || ansi || 0 || || awards || 0 || || banner || 0 || || calendar || 0 || || expert || 0 || || gen_regexps || 0 || || grep || 0 || || pretty || 0 || || scc || 0 || || cse || 1 || || eliza || 1 || || lift || 1 || || mkhprog || 1 || || prolog || 1 || || sorting || 1 || || veritas || 1 || || knights || 2 || || minimax || 2 || || x2n1 || 2 || || mandel2 || 3 || || parstof || 3 || || fluid || 4 || || pic || 4 || || boyer2 || 5 || || bspt || 5 || || cryptarithm2 || 5 || || fish || 6 || || gg || 6 || || reptile || 6 || || symalg || 6 || || tak || 6 || || VSD || 7 || || rfib || 7 || || queens || 9 || || rewrite || 9 || || sched || 11 || || fem || 12 || || fibheaps || 13 || || parser || 14 || || rsa || 14 || || genfft || 15 || || clausify || 17 || || gamteb || 17 || || fft || 18 || || boyer || 20 || || gcd || 20 || || sphere || 21 || || fft2 || 23 || || infer || 25 || || maillist || 25 || || mandel || 27 || || nucleic2 || 30 || || primes || 34 || || cichelli || 35 || || ida || 39 || || listcompr || 41 || || listcopy || 43 || || multiplier || 43 || || wang || 43 || || hpg || 45 || || anna || 46 || || reverse-complem || 46 || || integrate || 48 || || primetest || 50 || || paraffins || 54 || || solid || 54 || || puzzle || 55 || || treejoin || 61 || || compress2 || 64 || || compress || 65 || || event || 65 || || bernouilli || 74 || || comp_lab_zift || 78 || || simple || 86 || || wheel-sieve2 || 91 || || life || 100 || || exp3_8 || 102 || || wave4main || 103 || || typecheck || 106 || || atom || 110 || || fulsom || 112 || || CS || 116 || || para || 120 || || kahan || 138 || || transform || 145 || || power || 150 || || cacheprof || 151 || || hidden || 160 || || scs || 168 || || lcss || 175 || || wheel-sieve1 || 199 || || VS || 204 || || pidigits || 216 || || FS || 222 || || last-piece || 230 || || fasta || 263 || || cryptarithm1 || 264 || || CSD || 272 || || digits-of-e1 || 273 || || binary-trees || 342 || || digits-of-e2 || 381 || || circsim || 418 || || S || 451 || || VSM || 497 || || lambda || 617 || || integer || 905 || || n-body || 1043 || || linear || 1070 || || spectral-norm || 1132 || || constraints || 1171 || || exact-reals || 1289 || || mate || 1955 || || fannkuch-redux || 2185 || || k-nucleotide || 2989 || || 17 || || gamteb || 17 || || fft || 18 || || boyer || 20 || || gcd || 20 || || sphere || 21 || || fft2 || 23 || || infer || 25 || || maillist || 25 || || mandel || 27 || || nucleic2 || 30 || || primes || 34 || || cichelli || 35 || || ida || 39 || || listcompr || 41 || || listcopy || 43 || || multiplier || 43 || || wang || 43 || || hpg || 45 || || anna || 46 || || reverse-complem || 46 || || integrate || 48 || || primetest || 50 || || paraffins || 54 || || solid || 54 || || puzzle || 55 || || treejoin || 61 || || compress2 || 64 || || compress || 65 || || event || 65 || || bernouilli || 74 || || comp_lab_zift || 78 || || simple || 86 || || wheel-sieve2 || 91 || || life || 100 || || exp3_8 || 102 || || wave4main || 103 || || typecheck || 106 || || atom || 110 || || fulsom || 112 || || CS || 116 || || para || 120 || || kahan || 138 || || transform || 145 || || power || 150 || || cacheprof || 151 || || hidden || 160 || || scs || 168 || || lcss || 175 || || wheel-sieve1 || 199 || || VS || 204 || || pidigits || 216 || || FS || 222 || || last-piece || 230 || || fasta || 263 || || cryptarithm1 || 264 || || CSD || 272 || || digits-of-e1 || 273 || || binary-trees || 342 || || digits-of-e2 || 381 || || circsim || 418 || || S || 451 || || VSM || 497 || || lambda || 617 || || integer || 905 || || n-body || 1043 || || linear || 1070 || || spectral-norm || 1132 || || constraints || 1171 || || exact-reals || 1289 || || mate || 1955 || || fannkuch-redux || 2185 || || k-nucleotide || 2989 || -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15357> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 14

[GHC] #14271: ghci hangs with -fexternal-interpreter -prof
by GHC 09 Jan '19

09 Jan '19

#14271: ghci hangs with -fexternal-interpreter -prof ----------------------------------------+------------------------------- Reporter: AndreasK | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 8.2.1 Keywords: | Operating System: Windows Architecture: Unknown/Multiple | Type of failure: GHCi crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ----------------------------------------+------------------------------- {{{ ghci -fexternal-interpreter -prof GHCi, version 8.2.1: http://www.haskell.org/ghc/ :? for help Access violation in generated code when reading 00000001001e0418 }}} * The address remains the same between reruns (and reinstalls) of ghc. * Closing the hanging process leaves the launched ghc active in the background. * The directory I launch ghci from doesn't seem to matter. * I have only tried it on my desktop so far (Win10/Skylake) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14271> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 13

[GHC] #14576: Internal error when compiling TH code with profiling on Windows
by GHC 09 Jan '19

09 Jan '19

#14576: Internal error when compiling TH code with profiling on Windows -------------------------------------+------------------------------------- Reporter: lazac | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHC API | Version: 8.2.1 Keywords: | Operating System: Unknown/Multiple Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When using the GHC API with this minimal example, compiled with profiling enabled: {{{#!hs module Main where import GHC import GHC.Paths ( libdir ) main = runGhc (Just libdir) $ do env <- getSession dflags <- getSessionDynFlags setSessionDynFlags dflags target <- guessTarget "A.hs" Nothing setTargets [target] load LoadAllTargets }}} Invoking the main executable: {{{ testprof }}} While A.hs contains a TH splice: {{{#!hs {-# LANGUAGE TemplateHaskell #-} module A where $(return []) }}} The compiler crashes: {{{ testprof.exe: internal error: IMAGE_REL_AMD64_ADDR32[NB]: High bits are set in 10e6109d0 for .text (GHC version 8.2.1 for x86_64_unknown_mingw32) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug This application has requested the Runtime to terminate it in an unusual way. Please contact the application's support team for more information. }}} The walkaround is to use -fexternal-interpreter, in that case, the crash does not happen. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14576> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 5

[GHC] #15578: Honour INLINE pragmas on 0-arity bindings
by GHC 08 Jan '19

08 Jan '19

#15578: Honour INLINE pragmas on 0-arity bindings -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 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: -------------------------------------+------------------------------------- Currently if we see {{{ x = factorial 200 {-# INLINE x #-} f y = ...x... }}} we won't inline `x`, lest we duplicate the work of `factorial 200`. But * Occasionally it's very important to inline `x`: see Trac #15519 for a real-world example. * Suppose `x` is used exactly once, not inside a lambda, thus {{{ x = blah {-# INLINE x #-} g = ...x... }}} Then, if there is ''no'' INLINE pragma, `x` will get inlined (by `preInlineUnconditionally`. But if there ''is'' an INLINE pragma, currently `x` is ''not'' inlined by `preInlineUnconditionally`: see `Note [Stable unfoldings and preInlineUnconditionally]` in `SimplUtils`. This is insane! * INLINE says "inline me at every saturated call", where "saturated" is determined by the number of arguments syntactically to the left of the "=" in the source bindings. In this case, there are no arguments to the left, so every occurrence is saturated. So it's inconsistent not to inline. Bottom line: if a 0-ary binding has an INLINE pragma, I think we should inline it at every use site * Regardless of the work duplication * Including inside lambdas Note, however, that there is a real risk that full laziness will float it right back out again. Consider again {{{ x = factorial 200 {-# INLINE x #-} f y = ...x... }}} After inlining we get {{{ f y = ...(factorial 200)... }}} but it's entirely possible that full laziness will do {{{ lvl23 = factorial 200 f y = l...lvl23... }}} That's a problem for another day. Presumably the reason the user wanted to inline it was to get some rule to fire, and this change gives at least some chance that will happen, and makes INLINE behave consistently. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15578> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 22

[GHC] #13962: GHCi allows unsaturated type family
by GHC 08 Jan '19

08 Jan '19

#13962: GHCi allows unsaturated type family -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) 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: -------------------------------------+------------------------------------- Taken from [http://ics.p.lodz.pl/~stolarek/_media/pl:research:promotion- haskell14-slides.pdf Promoting Functions to Type Families in Haskell] {{{#!hs {-# Language TypeFamilies, PolyKinds, DataKinds, TypeOperators #-} type family Map (f :: a -> b) (xs :: [a]) :: [b] where Map f '[] = '[] Map f (x ': xs) = f x ': Map f xs data N = O | S N type family Pred (n :: N) :: N where Pred O = O Pred (S n) = n -- The type family ‘Map’ should have 2 arguments, but has been given 1 type MapPred = Map Pred }}} fails as expected, but it works in GHCi {{{ ghci> :kind Map Pred Map Pred :: [N] -> [N] ghci> :kind! Map Pred '[S (S O), S O, O] Map Pred '[S (S O), S O, O] :: [N] = '['S 'O, 'O, 'O] }}} I can only test this in GHC 7.8, 8 now. I know GHCi has weird rules for unsaturated type families but I figured I'd write a ticket because the slides say "But it is invalid to write: `Map Pred '[O, S O]`". -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13962> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 7

[GHC] #14677: Code generator does not correctly tag a pointer
by GHC 08 Jan '19

08 Jan '19

#14677: Code generator does not correctly tag a pointer -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 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: -------------------------------------+------------------------------------- Consider {{{ data T a = MkT ![a] }}} The pointer stored in a `MkT` constructor should always be correctly tagged, never tagged with un-evaluated 00. C.f. [wiki:Commentary/Rts/HaskellExecution/PointerTagging] But this invariant is broken. Example taken from #14626, comment:37-39. Trac14626_1.hs {{{ module Trac14626_1 where data Style = UserStyle Int | PprDebug data SDC = SDC !Style !Int defaultUserStyle :: Bool -> Style defaultUserStyle True = UserStyle 123 defaultUserStyle False = PprDebug }}} Trac14626_2.hs {{{ module Trac14626_2 where import Trac14626_1 f :: Int -> SDC f x = SDC (defaultUserStyle (x > 1)) x }}} Compiling with `ghc Trac14626_1 Trac14626_2 -ddump-simpl -O` results in a similar scenario than the one described by Heisenbug: {{{ -- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0} defaultUserStyle2 defaultUserStyle2 = I# 123# -- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0} defaultUserStyle1 defaultUserStyle1 = UserStyle defaultUserStyle2 -- RHS size: {terms: 7, types: 2, coercions: 0, joins: 0/0} defaultUserStyle defaultUserStyle = \ ds_dZ7 -> case ds_dZ7 of { False -> PprDebug; True -> defaultUserStyle1 } }}} Our `UserStyle 123` constant has been lifted to top-level, just like in Heisenbugs example. Now looking at the Core of `f` {{{ f f = \ x_a1dk -> case x_a1dk of { I# x1_a2gV -> case ># x1_a2gV 1# of { __DEFAULT -> SDC PprDebug x1_a2gV; 1# -> SDC defaultUserStyle1 x1_a2gV } } }}} (Note how `f` doesn't scrutinise defaultUserStyle1) Looking at the CMM for `f` we can see {{{ ... if (%MO_S_Le_W64(_s2hT::I64, 1)) goto c2ip; else goto c2is; c2ip: I64[Hp - 16] = SDC_con_info; P64[Hp - 8] = PprDebug_closure+2; I64[Hp] = _s2hT::I64; R1 = Hp - 15; Sp = Sp + 8; call (P64[Sp])(R1) args: 8, res: 0, upd: 8; c2is: I64[Hp - 16] = SDC_con_info; P64[Hp - 8] = defaultUserStyle1_closure; -- defaultUserStyle1 isn't tagged! I64[Hp] = _s2hT::I64; R1 = Hp - 15; Sp = Sp + 8; call (P64[Sp])(R1) args: 8, res: 0, upd: 8; }}} When generating code for f the code generator wants to know the `LambdaFormInfo` (the closure type) of `defaultUserStyle1`. Since `defaultUserStyle1` is defined in another module we end up calling `mkLFImported` in `StgCmmClosure` which ultimatively gives an `LFUnknown` which always gets a `DynTag` 0 from `lfDynTag`. I think we lack a bit of information here to give defaultUserStyle1 the correct `LFCon` lambda form. Maybe top-level binders should know its `LambdaForm` and include them in their interfaces. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14677> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 33

[GHC] #13742: Code using ConstraintKinds needs explicit kind signature with GHC 8.2.1
by GHC 08 Jan '19

08 Jan '19

#13742: Code using ConstraintKinds needs explicit kind signature with GHC 8.2.1 -------------------------------------+------------------------------------- Reporter: albertov | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 (Type checker) | Keywords: | Operating System: Unknown/Multiple ConstraintKinds, KindSignatures | Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The attached module compiles without errors with GHC 8.0.1 but needs an explicit kind signature with GHC 8.2.1-rc2. Mentioned in this [https://mail.haskell.org/pipermail/ghc- devs/2017-May/014222.html ghc-dev thread]. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13742> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 13

[GHC] #11621: GHC doesn't see () as a Constraint in type family
by GHC 08 Jan '19

08 Jan '19

#11621: GHC doesn't see () as a Constraint in type family -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: 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: -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE DataKinds, TypeOperators, KindSignatures, MultiParamTypeClasses, TypeFamilies #-} import Data.Kind class NotFound type family F b where F 'False = (NotFound :: Constraint) F 'True = (() :: Constraint) }}} works fine. Removing all constraints and final line it works without any annotations and infers the type of `F :: Bool -> Constraint`: {{{#!hs type family F b where F 'False = NotFound }}} GHC seems determined that `() :: Type` unless explicitly told otherwise, I would like to be able to write: {{{#!hs type family F b where F 'False = NotFound F 'True = () }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11621> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 11

[GHC] #14331: Overzealous free-floating kind check causes deriving clause to be rejected
by GHC 07 Jan '19

07 Jan '19

#14331: Overzealous free-floating kind check causes deriving clause to be rejected -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 (Type checker) | Keywords: deriving | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- GHC rejects this program: {{{#!hs {-# LANGUAGE DeriveAnyClass #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE PolyKinds #-} module Bug where class C a b data D = D deriving (C (a :: k)) }}} {{{ GHCi, version 8.2.1: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:8:1: error: Kind variable ‘k’ is implicitly bound in datatype ‘D’, but does not appear as the kind of any of its type variables. Perhaps you meant to bind it (with TypeInType) explicitly somewhere? | 8 | data D = D deriving (C (a :: k)) | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ }}} But it really shouldn't, since it's quite possible to write the code that is should generate: {{{#!hs instance C (a :: k) D }}} Curiously, this does not appear to happen for data family instances, as this typechecks: {{{#!hs {-# LANGUAGE DeriveAnyClass #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE TypeFamilies #-} module Bug where class C a b data family D1 data instance D1 = D1 deriving (C (a :: k)) class E where data D2 instance E where data D2 = D2 deriving (C (a :: k)) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14331> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 64