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[GHC] #15897: Negative MUT time in +RTS -s -RTS when heap profiling is enabled
by GHC 06 Feb '19

06 Feb '19

#15897: Negative MUT time in +RTS -s -RTS when heap profiling is enabled -------------------------------------+------------------------------------- Reporter: maoe | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.3 Component: Profiling | Version: 8.6.2 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Debugging (amd64) | information is incorrect Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Mutator run time in +RTS -s -RTS can go negative in GHC 8.6.x when retainer profiling is enabled. Here is an example taken from https://ghc.haskell.org/trac/ghc/ticket/881#comment:9 {{{ {-# OPTIONS_GHC -fprof-auto #-} import Control.Monad import Data.IORef import System.Environment main = do [n] <- getArgs replicateM (read n) (newIORef [1,2,3]) }}} {{{ % ghc-8.6.2 -prof -rtsopts -fforce-recomp repro.hs [1 of 1] Compiling Main ( repro.hs, repro.o ) Linking repro ... % ./repro 10000000 +RTS -s -h 3,053,080,472 bytes allocated in the heap 5,538,404,848 bytes copied during GC 1,013,615,328 bytes maximum residency (16 sample(s)) 36,422,944 bytes maximum slop 966 MB total memory in use (0 MB lost due to fragmentation) Tot time (elapsed) Avg pause Max pause Gen 0 2600 colls, 0 par 1.375s 1.376s 0.0005s 0.0019s Gen 1 16 colls, 0 par 4.355s 4.355s 0.2722s 1.0136s INIT time 0.000s ( 0.000s elapsed) MUT time 0.000s ( -0.833s elapsed) GC time 4.016s ( 4.016s elapsed) RP time 0.000s ( 0.000s elapsed) PROF time 1.715s ( 1.715s elapsed) EXIT time 1.715s ( 1.715s elapsed) Total time 6.612s ( 6.612s elapsed) %GC time 0.0% (0.0% elapsed) Alloc rate 0 bytes per MUT second Productivity -12.6% of total user, -12.6% of total elapsed }}} Here is what I found so far: * GHC 8.6.1, 8.6.2, and yesterday's HEAD have the same issue. GHC 8.4.4 doesn't have this issue. * `-hr` has the same issue. `-hT` is fine. * Without heap profiling the numbers this doesn't happen -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15897> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16146: Trivial partial type signature kills type inference in the presence of GADTs
by GHC 05 Feb '19

05 Feb '19

#16146: Trivial partial type signature kills type inference in the presence of GADTs -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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: -------------------------------------+------------------------------------- Suppose we have {{{#!hs data G a where G1 :: G Char G2 :: G Bool }}} If I now write {{{#!hs foo x = case x of G1 -> 'z' G2 -> True }}} I rightly get an error around untouchable variables. If I add the type signature {{{#!hs foo :: G a -> a }}} all is well again. So far, so good. Now, I write {{{#!hs foo :: forall a. G a -> a foo x = ((case x of G1 -> 'z' G2 -> True) :: _) }}} and I get those untouchable errors again. Untouchable-variable errors usually arise when there are multiple possible answers to the type inference problem. Yet, that isn't the case here: `_` must stand for `a`. Solution: mumble mumble bidirectional type inference mumble mumble. Part of the problem comes from Note [Partial expression signatures] in TcExpr, which states {{{ here is a guiding principile e :: ty should behave like let x :: ty x = e in x }}} Indeed, if we behave like that, the untouchable-variable errors are to be expected. But I also think that it would be a nice principle to say that `:: _` is always a no-op. This is not an idle nice-to-have: if we fix this, `singletons` will continue to work with GHC. Right now, it doesn't: https://github.com/goldfirere/singletons/issues/357 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16146> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16290: Export `noinline` function from `GHC.Exts`
by GHC 05 Feb '19

05 Feb '19

#16290: Export `noinline` function from `GHC.Exts` -------------------------------------+------------------------------------- Reporter: Ptharien's | Owner: (none) Flame | Type: feature | Status: new request | Priority: normal | Milestone: Component: | Version: 8.6.3 libraries/base | Keywords: noinline | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The other `id`s-with-special-behavior `inline`, `lazy`, and `oneShot` that are declared in `GHC.Magic` are re-exported from `GHC.Exts` (and thus made user-accessible), but `noinline` isn’t. This seems like an oversight. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16290> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16134: Continuous integration on FreeBSD
by GHC 05 Feb '19

05 Feb '19

#16134: Continuous integration on FreeBSD -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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: -------------------------------------+------------------------------------- Arrowd has been looking at introducing CI for FreeBSD/amd64. He has a build script using poudriere [[http://arrowd.name/ghc-ci|here]] -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16134> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16269: Postfix operator precedence
by GHC 05 Feb '19

05 Feb '19

#16269: Postfix operator precedence -------------------------------------+------------------------------------- Reporter: anuyts | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 (Parser) | Keywords: fixity | Operating System: Unknown/Multiple PostfixOperators | Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I want to define a postfix operator $- that feeds a default argument (obtained from a typeclass) to a given function. However, I would like to be able to write things like (f $ g $ h $-) for (f (g (h (defaultArg)))). This is not allowed, as $ has precedence 0 and $- is required to have lower precedence, which is impossible. I think it would be sensible if $- was required to have precedence at most infixr 0 (which is the precedence of $). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16269> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16281: PatternSynonyms doesn't accept non-prenex quantified functions, doesn't float foralls
by GHC 05 Feb '19

05 Feb '19

#16281: PatternSynonyms doesn't accept non-prenex quantified functions, doesn't float foralls -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.7 Keywords: | Operating System: Unknown/Multiple PatternSynonyms | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This works under GHC HEAD (8.7.20190115) {{{#!hs {-# Language RankNTypes #-} {-# Language ViewPatterns #-} {-# Language PatternSynonyms #-} newtype Logic a = Logic (forall xx. (a -> (xx -> xx)) -> (xx -> xx)) runLogic :: Logic a -> forall xx. (a -> xx -> xx) -> (xx -> xx) runLogic (Logic logic) = logic pattern L :: (forall xx. (a -> xx -> xx) -> xx -> xx) -> Logic a pattern L f <- (runLogic -> f) }}} I was under the impression that these would be equivalent {{{#!hs runLogic :: Logic a -> forall xx. (a -> xx -> xx) -> (xx -> xx) runLogic :: Logic a -> (a -> xx -> xx) -> (xx -> xx) }}} apart from the order of visible type application and such, but it fails: {{{#!hs {-# Language RankNTypes #-} {-# Language ViewPatterns #-} {-# Language PatternSynonyms #-} newtype Logic a = Logic (forall xx. (a -> (xx -> xx)) -> (xx -> xx)) runLogic :: Logic a -> (a -> xx -> xx) -> (xx -> xx) runLogic (Logic logic) = logic pattern L :: (forall xx. (a -> xx -> xx) -> xx -> xx) -> Logic a pattern L f <- (runLogic -> f) }}} {{{ $ ... -ignore-dot-ghci 1022_bug.hs GHCi, version 8.7.20190115: https://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( 1022_bug.hs, interpreted ) 1022_bug.hs:11:29: error: • Couldn't match expected type ‘forall xx. (a -> xx -> xx) -> xx -> xx’ with actual type ‘(a -> xx0 -> xx0) -> xx0 -> xx0’ • In the declaration for pattern synonym ‘L’ • Relevant bindings include f :: (a -> xx0 -> xx0) -> xx0 -> xx0 (bound at 1022_bug.hs:11:29) | 11 | pattern L f <- (runLogic -> f) | ^ Failed, no modules loaded. Prelude> }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16281> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15558: Locally handling an empty constraint
by GHC 05 Feb '19

05 Feb '19

#15558: Locally handling an empty constraint -------------------------------------+------------------------------------- Reporter: Ericson2314 | Owner: (none) Type: task | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 8.0.1 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: -------------------------------------+------------------------------------- I need something like `\case {}` for constraints. See the code below. There's nothing I can replace the `undefined` with that will satisfy the type checker. The dead code warning also bubbled up out of the field incorrectly. I think this will require new language features tangentially related to Lambdas for `forall`. (Both `forall _.` and `=>` are invisible quantifiers.) I will link this ticket in that GHC proposal, but am making it's own issue in the first place in case this is a genuine bug that can be fixed by less intrusive means. {{{ {-# LANGUAGE RankNTypes #-} {-# LANGUAGE EmptyCase #-} {-# LANGUAGE LambdaCase #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE ScopedTypeVariables #-} module Asdf where import Data.Kind import Data.Type.Equality data Sing a where X :: Sing Int Y :: Sing [Bool] data Foo a = Foo a (forall b. [b] :~: a -> b) data Bar a = Bar a (forall b. [b] ~ a => b) f, f' :: forall a. Sing a -> Foo a f s = Foo a b where a :: a a = case s of X -> 0 Y -> [] b :: forall b. [b] :~: a -> b b = case s of X -> \case {} Y -> \Refl -> False f' = \case X -> Foo 0 (\case {}) Y -> Foo [] (\Refl -> False) g, g' :: forall a. Sing a -> Bar a g s = Bar a b where a :: a a = case s of X -> 0 Y -> [] b :: forall b. [b] ~ a => b b = case s of Y -> False g' = \case X -> Bar 0 undefined -- can't make this happy Y -> Bar [] False }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15558> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16178: Brackets and splices should be overloaded like the static keyword
by GHC 05 Feb '19

05 Feb '19

#16178: Brackets and splices should be overloaded like the static keyword -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Template | Version: 8.6.3 Haskell | Keywords: | Operating System: Unknown/Multiple TypedTemplateHaskell | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- It's quite convenient that the `static` keyword is rebindable. To recap, if `e :: T` then `static e :: (IsStatic p) => p t`. It should also be possible rebind brackets and splices in the same manner. So we introduce two type classes `IsBracket` and `IsSplice`. Now quoting a term `e :: T` has type `e :: IsBracket p => p T` and the argument to a splice must have type `e :: IsSplice p => p T` which results in a value of type `T`. {{{ class IsBracket p where fromBracket :: Code t -> p t class IsSplice p where toBracket :: p t -> Code t foo :: IsBracket p => p Int foo = [|| 5 ||] qux :: (IsSplice p, IsBracket p) => Int qux = $$(foo) }}} As an aside, arguably the `static` form should only be rebindable when `RebindableSyntax` is enabled but that boat seems to have sailed. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16178> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12149: Support bit-fields
by GHC 05 Feb '19

05 Feb '19

#12149: Support bit-fields -------------------------------------+------------------------------------- Reporter: | Owner: facundo.dominguez | Type: bug | Status: new Priority: normal | Milestone: Component: hsc2hs | Version: 8.0.1 Keywords: bit-fields | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Having C type like: {{{ typedef struct S { int f0: 1; int f1: 15; } S; }}} and {{{hsc}}} code like {{{ #{peek S, f0} p }}} Causes {{{hsc2hs}}} to fail with {{{ error: attempt to take address of bit-field structure member 'f0' }}} Apparently this is an error from gcc, which cannot provide the address of bit-fields. However, in Haskell we are not interested in the address of the bit-field but in its value. It would be useful to have a way to get and set the values of these fields. Some former discussion [https://mail.haskell.org/pipermail/haskell- cafe/2008-November/050317.html here] -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12149> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16092: Bug when trying to combine two lists
by GHC 05 Feb '19

05 Feb '19

#16092: Bug when trying to combine two lists -------------------------------------+------------------------------------- Reporter: sutbult | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: MacOS X Architecture: x86_64 | Type of failure: Building GHC (amd64) | failed Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I want to write a function that takes two lists and returns a list that includes every possible combination of elements from the two given lists, using a given function. I thought that this code would work: {{{#!hs combine :: (a -> b -> c) [a] -> [b] -> [c] combine fn alist blist = [fn a b | a <- alist, b <- blist] }}} However, when compiling, this message arises from GHC: Glasgow Haskell Compiler, Version 8.2.1, stage 2 booted by GHC version 7.10.3 Using binary package database: /Library/Frameworks/GHC.framework/Versions/8.2.1-x86_64/usr/lib/ghc-8.2.1/package.conf.d/package.cache Using binary package database: /Users/samuelutbult/.ghc/x86_64-darwin-8.2.1/package.conf.d/package.cache package flags [] loading package database /Library/Frameworks/GHC.framework/Versions/8.2.1-x86_64/usr/lib/ghc-8.2.1/package.conf.d loading package database /Users/samuelutbult/.ghc/x86_64-darwin-8.2.1/package.conf.d wired-in package ghc-prim mapped to ghc-prim-0.5.1.0 wired-in package integer-gmp mapped to integer-gmp-1.0.1.0 wired-in package base mapped to base-4.10.0.0 wired-in package rts mapped to rts wired-in package template-haskell mapped to template-haskell-2.12.0.0 wired-in package ghc mapped to ghc-8.2.1 wired-in package dph-seq not found. wired-in package dph-par not found. package flags [] loading package database /Library/Frameworks/GHC.framework/Versions/8.2.1-x86_64/usr/lib/ghc-8.2.1/package.conf.d loading package database /Users/samuelutbult/.ghc/x86_64-darwin-8.2.1/package.conf.d wired-in package ghc-prim mapped to ghc-prim-0.5.1.0 wired-in package integer-gmp mapped to integer-gmp-1.0.1.0 wired-in package base mapped to base-4.10.0.0 wired-in package rts mapped to rts-1.0 wired-in package template-haskell mapped to template-haskell-2.12.0.0 wired-in package ghc mapped to ghc-8.2.1 wired-in package dph-seq not found. wired-in package dph-par not found. *** Chasing dependencies: Chasing modules from: *Combine.hs !!! Chasing dependencies: finished in 0.69 milliseconds, allocated 0.222 megabytes Stable obj: [] Stable BCO: [] Ready for upsweep [NONREC ModSummary { ms_hs_date = 2018-12-23 17:18:05.830132761 UTC ms_mod = Main, ms_textual_imps = [(Nothing, Prelude)] ms_srcimps = [] }] *** Deleting temp files: Deleting: compile: input file Combine.hs *** Checking old interface for Main (use -ddump-hi-diffs for more details): [1 of 1] Compiling Main ( Combine.hs, Combine.o ) *** Parser [Main]: !!! Parser [Main]: finished in 1.05 milliseconds, allocated 0.171 megabytes *** Renamer/typechecker [Main]: *** Deleting temp files: Deleting: *** Deleting temp dirs: Deleting: ghc: panic! (the 'impossible' happened) (GHC version 8.2.1 for x86_64-apple-darwin): repSplitAppTys a_anL[sk:1] b_anM[sk:1] -> c_anN[sk:1] [] Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable pprPanic, called at compiler/types/Type.hs:808:9 in ghc:Type Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16092> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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