December 2017 - ghc-tickets

[GHC] #14196: Replace ArrayArray# with either UnliftedArray# or Array#
by GHC 28 Feb '18

28 Feb '18

#14196: Replace ArrayArray# with either UnliftedArray# or Array# -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: Unknown/Multiple LevityPolymorphism | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Just to be clear, there currently is nothing named `UnliftedArray#`. I would like to propose that such a thing possibly be added, with the long- term goal of deprecating and removing `ArrayArray#`. The interface for it would look like this: {{{#!hs data UnliftedArray# (a :: TYPE 'UnliftedRep) data MutableUnliftedArray# s (a :: TYPE 'UnliftedRep) indexUnliftedArray# :: forall (a :: TYPE 'UnliftedRep). UnliftedArray# a -> Int# -> a writeUnliftedArray# :: forall (a :: TYPE 'UnliftedRep). MutableUnliftedArray# s a -> Int# -> a -> State# s -> State# s readUnliftedArray# :: forall (a :: TYPE 'UnliftedRep). MutableUnliftedArray# s a -> Int# -> State# s -> (# State# s, a #) unsafeFreezeUnliftedArray# :: forall (a :: TYPE 'UnliftedRep). MutableUnliftedArray# s a -> State# s -> (#State# s, UnliftedArray# a#) newUnliftedArray# :: forall (a :: TYPE 'UnliftedRep). Int# -> a -> State# s -> (# State# s, MutableUnliftedArray# s a #) }}} You would also have a few other things like `sameMutableUnliftedArray#`, `sizeofMutableArray#`, `unsafeThawUnliftedArray#`, `copyUnliftedArray#`, etc. The main difficulty that I see in doing this is that I'm not sure if you can tell a primop that it takes a polymorphic argument whose kind is something other than `TYPE LiftedRep`. The bodies of all of the functions I listed above could simply be copied from the `ArrayArray#` functions. There are a few alternatives I've heard discussed. One is to make `Array#` accepted both boxed or unboxed types. There is a brief discussion of this in the UnliftedDataTypes proposal [#point0 (0)]. Indeed, it appears that some have managed to smuggle unlifted data into `Array#` already, with the caveats one would expect [#point1 (1)]. This interface would look like: {{{#!hs data Array# (a :: TYPE k) data MutableArray# s (a :: TYPE k) indexArray# :: Array# a -> Int -> a -- same as before indexUnliftedArray# :: forall (a :: TYPE UnliftedRep). Array# a -> Int -> a }}} So instead of having `Array#` and `UnliftedArray#` as separate data types, we could have `Array#` handle both cases, but we would need to make a duplicate of every function that operates on `Array#`. This follows all of the appropriate rules for when levity polymorphism is allowed, and it should be backwards-compatible with the previous non-levity-polymorphic definition of `Array#`. I'm not sure how many things in the GHC runtime assume that the values inside an array are lifted, so this might cause a bunch of problems. If it is possible, this approach would be kind of neat because then `SmallArray#` could be similarly adapted. Anyway, I just wanted to get this out there. I would be happy to try implementing the first proposal (involving `UnliftedArray#`) at some point in the next six months. Any feedback on the idea would be appreciated. Also, any comments on how appropriate this is for someone new to contributing to GHC would be appreciated as well. Thanks. * [=#point0 (0)] https://ghc.haskell.org/trac/ghc/wiki/UnliftedDataTypes#Parametricity * [=#point0 (1)] https://www.reddit.com/r/haskell/comments/6v9rmg/an_unified_array_interface… -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14196> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13075: Top-level bang pattern accepted
by GHC 27 Feb '18

27 Feb '18

#13075: Top-level bang pattern accepted -------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire 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: -------------------------------------+------------------------------------- When I compile/link {{{#!hs {-# LANGUAGE BangPatterns #-} module Main where !(Just x) = Nothing main = putStrLn "hi there!" }}} I get {{{ rae:09:50:49 ~/temp> ghc Bug.hs [1 of 1] Compiling Main ( Bug.hs, Bug.o ) Linking Bug ... ld: can't open output file for writing: Bug, errno=21 for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation) `gcc' failed in phase `Linker'. (Exit code: 1) }}} This bogus code should be rejected more gracefully (and earlier). It actually also loads into GHCi, but shouldn't. Will fix while I'm in the area. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13075> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13596: Try disabling inlining of DynFlags combinators
by GHC 27 Feb '18

27 Feb '18

#13596: Try disabling inlining of DynFlags combinators -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: task | 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: -------------------------------------+------------------------------------- `DynFlags` requires a surprisingly amount of effort to compile. One thing I've been meaning to try is disabling inlining of `make_ord_flag` and such to characterize how much of an impact these inlinings have on simplification effort. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13596> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11107: Can't use type wildcard infix
by GHC 26 Feb '18

26 Feb '18

#11107: Can't use type wildcard infix -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 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: -------------------------------------+------------------------------------- This fails: {{{ foo :: Int `_a` Bool foo = Right True }}} But moving `_a` to be prefix works. I observe the same behavior with an unnamed type wildcard. This was discovered while poking around in the renamer, not in real code! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11107> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13088: Type operator holes don't work infix
by GHC 26 Feb '18

26 Feb '18

#13088: Type operator holes don't work infix -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Parser) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: #13050 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Originally noted in https://phabricator.haskell.org/D2910 (which fixed #13050). Currently, you can do this: Does this also work with TypeOperators? That is, you can do this: {{{#!hs {-# LANGUAGE TypeOperators #-} foo :: a `_over` b -> _over a b foo = id }}} But not this: {{{#!hs {-# LANGUAGE TypeOperators #-} foo :: a `_` b -> over a b foo = id }}} osa1 made an attempt at fixing this, and recorded his progress [https://phabricator.haskell.org/D2910#85423 here]: > I played with alternative implementations and attempted at implementing type-level version of this patch as suggested by @RyanGlScott. > > Since `_` needs special treatment by the renamer I think we have to have some kind of special treatment for `_` in the parser too, so this implementation may not be too bad. > > (alternatively I guess we could remove special treatment for `_` in the parser but that'd just move special cases to the renamer, so I'm not sure that's any better than the current approach) > > About the type-level named infix holes: Type renamer is quite different than term renamer (`RnTypes.hs`) and I don't understand type-checker parts of the compiler -- but I was able to made an attempt at implementing this > > {{{#!diff > diff --git a/compiler/hsSyn/HsTypes.hs b/compiler/hsSyn/HsTypes.hs > index 53f200f..877c243 100644 > --- a/compiler/hsSyn/HsTypes.hs > +++ b/compiler/hsSyn/HsTypes.hs > @@ -608,6 +608,7 @@ type LHsAppType name = Located (HsAppType name) > data HsAppType name > = HsAppInfix (Located name) -- either a symbol or an id in backticks > | HsAppPrefix (LHsType name) -- anything else, including things like (+) > + | HsAppWild (Located (HsWildCardInfo name)) > deriving instance (DataId name) => Data (HsAppType name) > > instance (OutputableBndrId name) => Outputable (HsAppType name) where > @@ -987,11 +988,18 @@ getAppsTyHead_maybe tys = case splitHsAppsTy tys of > splitHsAppsTy :: [LHsAppType name] -> ([[LHsType name]], [Located name]) > splitHsAppsTy = go [] [] [] > where > + go :: [LHsType name] > + -> [[LHsType name]] > + -> [Located name] > + -> [LHsAppType name] > + -> ([[LHsType name]], [Located name]) > go acc acc_non acc_sym [] = (reverse (reverse acc : acc_non), reverse acc_sym) > go acc acc_non acc_sym (L _ (HsAppPrefix ty) : rest) > = go (ty : acc) acc_non acc_sym rest > go acc acc_non acc_sym (L _ (HsAppInfix op) : rest) > = go [] (reverse acc : acc_non) (op : acc_sym) rest > + go acc acc_non acc_sym (L l (HsAppWild (L _ wc)) : rest) > + = go (L l (HsWildCardTy wc) : acc) acc_non acc_sym rest > > -- Retrieve the name of the "head" of a nested type application > -- somewhat like splitHsAppTys, but a little more thorough > @@ -1334,14 +1342,18 @@ ppr_fun_ty ctxt_prec ty1 ty2 > > -------------------------- > ppr_app_ty :: (OutputableBndrId name) => TyPrec -> HsAppType name -> SDoc > -ppr_app_ty _ (HsAppInfix (L _ n)) = pprInfixOcc n > +ppr_app_ty _ (HsAppInfix (L _ n)) > + = pprInfixOcc n > ppr_app_ty _ (HsAppPrefix (L _ (HsTyVar NotPromoted (L _ n)))) > = pprPrefixOcc n > ppr_app_ty _ (HsAppPrefix (L _ (HsTyVar Promoted (L _ n)))) > = space <> quote (pprPrefixOcc n) -- We need a space before the ' above, so > -- the parser does not attach it to the > -- previous symbol > -ppr_app_ty ctxt (HsAppPrefix ty) = ppr_mono_lty ctxt ty > +ppr_app_ty ctxt (HsAppPrefix ty) > + = ppr_mono_lty ctxt ty > +ppr_app_ty ctxt (HsAppWild (L _ (AnonWildCard _))) > + = empty -- FIXME > > -------------------------- > ppr_tylit :: HsTyLit -> SDoc > diff --git a/compiler/parser/Parser.y b/compiler/parser/Parser.y > index dfb6755..da4696a 100644 > --- a/compiler/parser/Parser.y > +++ b/compiler/parser/Parser.y > @@ -1833,6 +1833,7 @@ tyapp :: { LHsAppType RdrName } > [mj AnnSimpleQuote $1] } > | SIMPLEQUOTE varop {% ams (sLL $1 $> $ HsAppInfix $2) > [mj AnnSimpleQuote $1] } > + | '`' '_' '`' { sL1 $1 (HsAppWild (sL1 $1 (AnonWildCard PlaceHolder))) } > > atype :: { LHsType RdrName } > : ntgtycon { sL1 $1 (HsTyVar NotPromoted $1) } -- Not including unit tuples > diff --git a/compiler/rename/RnTypes.hs b/compiler/rename/RnTypes.hs > index f3fcf88..9298020 100644 > --- a/compiler/rename/RnTypes.hs > +++ b/compiler/rename/RnTypes.hs > @@ -1050,8 +1050,11 @@ collectAnonWildCards lty = go lty > > gos = mconcat . map go > > + prefix_types_only :: HsAppType Name -> Maybe (LHsType Name) > prefix_types_only (HsAppPrefix ty) = Just ty > prefix_types_only (HsAppInfix _) = Nothing > + prefix_types_only (HsAppWild (L l (AnonWildCard wc_name))) = > + Just (L l (HsWildCardTy (AnonWildCard wc_name))) > > collectAnonWildCardsBndrs :: [LHsTyVarBndr Name] -> [Name] > collectAnonWildCardsBndrs ltvs = concatMap (go . unLoc) ltvs > @@ -1646,8 +1649,9 @@ extract_apps t_or_k tys acc = foldrM (extract_app t_or_k) acc tys > > extract_app :: TypeOrKind -> LHsAppType RdrName -> FreeKiTyVars > -> RnM FreeKiTyVars > -extract_app t_or_k (L _ (HsAppInfix tv)) acc = extract_tv t_or_k tv acc > -extract_app t_or_k (L _ (HsAppPrefix ty)) acc = extract_lty t_or_k ty acc > +extract_app t_or_k (L _ (HsAppInfix tv)) acc = extract_tv t_or_k tv acc > +extract_app t_or_k (L _ (HsAppPrefix ty)) acc = extract_lty t_or_k ty acc > +extract_app t_or_k (L _ (HsAppWild (L l wc))) acc = extract_lty t_or_k (L l (HsWildCardTy wc)) acc > > extract_hs_tv_bndrs :: [LHsTyVarBndr RdrName] -> FreeKiTyVars > -> FreeKiTyVars -> RnM FreeKiTyVars > }}} > > Once I figure out how to do the `FIXME` part this patch may just work. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13088> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11777: RTS source code issues
by GHC 26 Feb '18

26 Feb '18

#11777: RTS source code issues -------------------------------------+------------------------------------- Reporter: simonpj | Owner: 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: -------------------------------------+------------------------------------- Tiago Silva <tiagosilva(a)hush.com> writes: Last night I started looking at the C files used in GHC and noticed these issues: {{{ /driver/utils/cwrapper.c : int main(int, char **); }}} `void *p` is apparently unused, even if the compiler optimizes it away.. you should check if something went missing. {{{ /rts/RetainerProfile.c : static nat sanityCheckHeapClosure(StgClosure *) }}} `StgInfoTable *info` has the same issue as above {{{ /rts/RetainerSet.c #elif defined(RETAINER_SCHEME_CC) // Retainer scheme 3: retainer = cost centre void printRetainerSetShort(FILE *f, RetainerSet *rs, nat max_length) { char tmp[max_length + 1]; int size; nat j; } }}} Unlike the other functions around it, this function does nothing. Its variables are also not unused? {{{ /rts/sm/MarkWeak.c : void markWeakPtrList (void); if (w->header.info == &stg_DEAD_WEAK_info) { last_w = &(w->link); } else { last_w = &(w->link); } }}} Not sure what's going on here. Regardless of the test the two branches do the same thing. {{{ /rts/win32/IOManager.c : AddIORequest, AddDelayRequest, AddProcRequest functions }}} If `(!ioMan || !wItem)` the functions either return 0 or FALSE, but they don't free `wItem` before. Is this optimized by the compiler? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11777> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14291: Tests tend to fail in the ext-interp when testing a tree built with a source distribution
by GHC 25 Feb '18

25 Feb '18

#14291: Tests tend to fail in the ext-interp when testing a tree built with a source distribution -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.2.1 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: -------------------------------------+------------------------------------- One issue I've noticed while working on #13716 is that most (if not all) of the tests runs in the `ext-interp` way fail when run inside a tree derived from a source distribution tarball. For instance, {{{ $ git clone git://git.haskell.org/ghc $ cd ghc $ git submodule update --init $ mk/get-win32-tarballs.sh download all $ ./boot $ ./configure $ make sdist $ mkdir tmp; cd tmp $ ls ../sdistprep/ghc-*-src.tar.xz | xargs -n1 tar -xf $ cd ghc-* $ ./boot $ ./configure $ make -j9 $ make test TEST=T10638 ... =====> T10638(normal) 1 of 1 [0, 0, 0] cd "./th/T10638.run" && "/mnt/work/ghc/ghc- testing/temp/ghc-8.3.20170927/inplace/bin/ghc-stage2" -c T10638.hs -dcore- lint -dcmm-lint -no-user-package-db -rtsopts -fno-warn-missed- specialisations -fshow-warning-groups -fdiagnostics-color=never -fno- diagnostics-show-caret -dno-debug-output -XTemplateHaskell -package template-haskell -v0 =====> T10638(ext-interp) 1 of 1 [0, 0, 0] cd "./th/T10638.run" && "/mnt/work/ghc/ghc- testing/temp/ghc-8.3.20170927/inplace/bin/ghc-stage2" -c T10638.hs -dcore- lint -dcmm-lint -no-user-package-db -rtsopts -fno-warn-missed- specialisations -fshow-warning-groups -fdiagnostics-color=never -fno- diagnostics-show-caret -dno-debug-output -XTemplateHaskell -package template-haskell -fexternal-interpreter -v0 Actual stderr output differs from expected: diff -uw "./th/T10638.run/T10638.stderr.normalised" "./th/T10638.run/T10638.comp.stderr.normalised" --- ./th/T10638.run/T10638.stderr.normalised 2017-09-27 12:18:45.737974039 -0400 +++ ./th/T10638.run/T10638.comp.stderr.normalised 2017-09-27 12:18:45.737974039 -0400 @@ -1,5 +1,18 @@ +ghc-iserv.bin: internal evacuate(static): strange closure type 16476 + (GHC version 8.3.20170927 for x86_64_unknown_linux) + Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug -T10638.hs:26:11: - ‘static test2’ is not a valid C identifier - When checking declaration: - foreign import prim safe "static test2" cmm_test2 :: Int# -> Int# +T10638.hs:26:9: + Exception when trying to run compile-time code: + {handle: <file descriptor: 11>}: GHCi.Message.remoteCall: end of file + Code: do t <- [t| Int# -> Int# |] + cmm_test2 <- newName "cmm_test2" + addTopDecls + [ForeignD (ImportF Prim Safe "static test2" cmm_test2 t)] + .... + In the untyped splice: + $(do t <- [t| Int# -> Int# |] + cmm_test2 <- newName "cmm_test2" + addTopDecls + [ForeignD (ImportF Prim Safe "static test2" cmm_test2 t)] + [| test1 |]) *** unexpected failure for T10638(ext-interp) Unexpected results from: TEST="T10638" ... }}} The crashes are generally RTS panics or segmentation faults. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14291> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13011: Simplifier ticks exhausted: a 10-line case
by GHC 25 Feb '18

25 Feb '18

#13011: Simplifier ticks exhausted: a 10-line case -------------------------------------+------------------------------------- Reporter: L.K.Rebellion | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Keywords: Simplifier | Operating System: Linux ticks exhausted | Type of failure: Compile-time Architecture: x86 | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: #8319 #12776 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I was trying to define a function that could take itself as an argument. {{{#!hs newtype MobiusFn a = MobiusFn { func :: MobiusFn a -> a } spin :: MobiusFn a -> a spin mf = func mf mf }}} Use it to find suffixes of a `String` {{{#!hs suffixes :: String -> [String] suffixes = spin $ MobiusFn suffixesMF where suffixesMF _ [] = [] suffixesMF mf s@(_:xs) = s : spin mf xs }}} Add `main` and compile {{{#!hs main = readLn >>= (print . suffixes) }}} The compiler panicked with {{{ [1 of 1] Compiling Main ( test.hs, test.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for i386-unknown-linux): Simplifier ticks exhausted When trying UnfoldingDone mf_s1UD }}} But if we ignore the empty string case, it works well with non-empty strings. {{{#!hs suffixes :: String -> [String] suffixes = spin $ MobiusFn suffixesMF where suffixesMF _ s@[_] = [s] suffixesMF mf s@(_:xs) = s : spin mf xs }}} Two versions tested. {{{ GHC version 8.0.1 for i386-unknown-linux GHC version 7.10.3 for i386-unknown-linux }}} Thank you for reading. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13011> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8597: Git Hook script to prevent large binary blobs being checked in
by GHC 24 Feb '18

24 Feb '18

#8597: Git Hook script to prevent large binary blobs being checked in ------------------------------------+------------------------------------- Reporter: hvr | Owner: hvr Type: task | Status: new Priority: normal | Milestone: Component: Trac & Git | Version: Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- It has already occurred in the past in `testsuite.git` repo, that executables were checked in by accident, and caused the Git history to get bloated. In order to avoid such accidents in the future a Git hook script in the style of [http://stackoverflow.com/questions/20226132/is-there-a-git-hook- which-can-prevent-binary-check-ins this] might be useful, but taking also into account the size, and/or possibly with a magic safeword to be put in the commit message, to override the check for a single commit, if the author really knows what (s)he's doing. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8597> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14542: Renamer / typechecker hang (UndecidableSuperClasses)
by GHC 24 Feb '18

24 Feb '18

#14542: Renamer / typechecker hang (UndecidableSuperClasses) -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 Keywords: | Operating System: Unknown/Multiple UndecidableSuperClasses | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Adapted from [https://gist.github.com/ekmett/b26363fc0f38777a637d hask], this does not look like a normal superclass loop. Loop is avoided by removing `instance (Category p, Category q) => Category (Nat p q)`. {{{#!hs {-# language KindSignatures #-} {-# language PolyKinds #-} {-# language DataKinds #-} {-# language TypeFamilies #-} {-# language RankNTypes #-} {-# language NoImplicitPrelude #-} {-# language FlexibleContexts #-} {-# language MultiParamTypeClasses #-} {-# language GADTs #-} {-# language ConstraintKinds #-} {-# language FlexibleInstances #-} {-# language TypeOperators #-} {-# language ScopedTypeVariables #-} {-# language DefaultSignatures #-} {-# language FunctionalDependencies #-} {-# language UndecidableSuperClasses #-} {-# language UndecidableInstances #-} {-# language TypeInType #-} import GHC.Types (Constraint, Type) type Cat i = i -> i -> Type newtype Y p a b = Y { getY :: p b a } class (Functor p, Dom p ~ Op p, Cod p ~ Nat p (->), Ob (Op p) ~ Ob p) => Category (p :: Cat i) where type Op p :: Cat i type Op p = Y p type Ob p :: i -> Constraint class (Category (Dom f), Category (Cod f)) => Functor (f :: i -> j) where type Dom f :: Cat i type Cod f :: Cat j data Nat :: Cat i -> Cat j -> Cat (i -> j) instance (Category p, Category q) => Category (Nat p q) }}} I get {{{ $ ghci2 -ignore-dot-ghci -v /tmp/Hangs.hs GHCi, version 8.3.20171122: http://www.haskell.org/ghc/ :? for help Glasgow Haskell Compiler, Version 8.3.20171122, stage 2 booted by GHC version 8.2.1 ... Loading package integer-gmp-1.0.1.0 ... linking ... done. Loading package base-4.11.0.0 ... linking ... done. *** Parser [source]: !!! Parser [source]: finished in 0.66 milliseconds, allocated 0.136 megabytes *** Desugar: *** Simplify [expr]: !!! Simplify [expr]: finished in 0.43 milliseconds, allocated 0.233 megabytes *** CorePrep [expr]: !!! CorePrep [expr]: finished in 0.23 milliseconds, allocated 0.167 megabytes *** ByteCodeGen [Ghci1]: !!! ByteCodeGen [Ghci1]: finished in 0.35 milliseconds, allocated 0.284 megabytes *** Parser [source]: !!! Parser [source]: finished in 0.21 milliseconds, allocated 0.197 megabytes *** Desugar: *** Simplify [expr]: !!! Simplify [expr]: finished in 0.52 milliseconds, allocated 0.268 megabytes *** CorePrep [expr]: !!! CorePrep [expr]: finished in 0.23 milliseconds, allocated 0.113 megabytes *** ByteCodeGen [Ghci1]: !!! ByteCodeGen [Ghci1]: finished in 0.46 milliseconds, allocated 0.334 megabytes *** Chasing dependencies: Chasing modules from: !!! Chasing dependencies: finished in 0.14 milliseconds, allocated 0.047 megabytes Stable obj: [] Stable BCO: [] unload: retaining objs [] unload: retaining bcos [] Ready for upsweep [] Upsweep completely successful. *** Deleting temp files: Deleting: *** Chasing dependencies: Chasing modules from: */tmp/Hangs.hs !!! Chasing dependencies: finished in 6.10 milliseconds, allocated 10.504 megabytes Stable obj: [] Stable BCO: [] unload: retaining objs [] unload: retaining bcos [] Ready for upsweep [NONREC ModSummary { ms_hs_date = 2017-11-28 22:14:57.810561584 UTC ms_mod = Main, ms_textual_imps = [(Nothing, GHC.Types)] ms_srcimps = [] }] *** Deleting temp files: Deleting: compile: input file /tmp/Hangs.hs *** Checking old interface for Main (use -ddump-hi-diffs for more details): [1 of 1] Compiling Main ( /tmp/Hangs.hs, interpreted ) *** Parser [Main]: !!! Parser [Main]: finished in 2.63 milliseconds, allocated 4.821 megabytes *** Renamer/typechecker [Main]: }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14542> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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