April 2016 - ghc-tickets

[GHC] #11655: Ambiguous types in pattern synonym not determined by functional dependencies
by GHC 07 May '16

07 May '16

#11655: Ambiguous types in pattern synonym not determined by functional dependencies -------------------------------------+------------------------------------- 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: -------------------------------------+------------------------------------- The Glorious Glasgow Haskell Compilation System, version 8.1.20160117 {{{#!hs {-# LANGUAGE UndecidableInstances, KindSignatures, DataKinds, GADTs, MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances #-} data Ty ty where I :: Ty Int A :: Ty a -> Ty [a] data NUM = MKINT data SCALAR = MKNUM NUM data TYPE = MKSCALAR SCALAR | MKARR TYPE -- Each type determines a TYPE -- Int -> MKSCALAR (MKNUM MKINT) -- [Int] -> MKARR (MKSCALAR (MKNUM MKINT)) class GetTy ty (rep :: TYPE) | ty -> rep where getTy :: Ty ty instance GetTy Int (MKSCALAR (MKNUM MKINT)) where getTy = I instance GetTy a rep => GetTy [a] (MKARR rep) where getTy = A getTy data Unary a b where Un :: (GetTy a a_rep, GetTy b b_rep) => UnOp a b -> (a -> b) -> Unary a b data UnOp a b where OpLen :: UnOp [a] Int data E a where UnOp :: Unary a b -> (E a -> E b) }}} Now I'd like to create an explicitly-bidirectional pattern synonym, defining a unidirectional pattern synonym works fine: {{{#!hs pattern Len xs <- UnOp (Un OpLen _) xs }}} but the inferred type is rejected: {{{#!hs -- >>> :i Len -- pattern Len :: () => (GetTy a a_rep, GetTy t b_rep, -- a GHC.Prim.~# [a1], t GHC.Prim.~# Int) => E a -> E t pattern Len :: () => (GetTy a a_rep, GetTy t b_rep, a ~ [a1], t ~ Int) => E a -> E t pattern Len xs <- UnOp (Un OpLen _) xs -- tgxg.hs:31:37-38: error: … -- • Could not deduce (GetTy a1 rep) arising from a pattern -- from the context: (GetTy a a_rep, GetTy t b_rep) -- bound by a pattern with constructor: -- Un :: forall a b (a_rep :: TYPE) (b_rep :: TYPE). -- (GetTy a a_rep, GetTy b b_rep) => -- UnOp a b -> (a -> b) -> Unary a b, -- in a pattern synonym declaration -- at /tmp/tgxg.hs:31:25-34 -- or from: (a ~ [a1], t ~ Int) -- bound by a pattern with constructor: -- OpLen :: forall a. UnOp [a] Int, -- in a pattern synonym declaration -- at /tmp/tgxg.hs:31:28-32 -- The type variable ‘rep’ is ambiguous -- • In the declaration for pattern synonym ‘Len’ -- Compilation failed. }}} Constructing it works fine: {{{#!hs len :: GetTy a rep => E [a] -> E Int len = UnOp (Un OpLen length) }}} but adding it to the pattern makes it fail: {{{#!hs pattern Len xs <- UnOp (Un OpLen _) xs where Len xs = len xs -- tgxg.hs:32:18-23: error: … -- • Could not deduce (GetTy a1 rep) arising from a use of ‘len’ -- from the context: (GetTy a a_rep, GetTy t b_rep, a ~ [a1], t ~ Int) -- bound by the type signature for: -- Main.$bLen :: (GetTy a a_rep, GetTy t b_rep, a ~ [a1], t ~ Int) => -- E a -> E t -- at /tmp/tgxg.hs:(31,1)-(32,23) -- The type variable ‘rep’ is ambiguous -- These potential instances exist: -- instance GetTy Int ('MKSCALAR ('MKNUM 'MKINT)) -- -- Defined at /tmp/tgxg.hs:14:10 -- instance GetTy a rep => GetTy [a] ('MKARR rep) -- -- Defined at /tmp/tgxg.hs:17:10 -- • In the expression: len xs -- In an equation for ‘$bLen’: $bLen xs = len xs -- Compilation failed. }}} Mixing functional dependencies, GADTs and pattern synonyms is confusing to me but is GHC correct that this type is ambiguous and if so what is missing? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11655> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11641: Allow wildcards for parameters functionally determined (also type synonyms)
by GHC 07 May '16

07 May '16

#11641: Allow wildcards for parameters functionally determined (also type synonyms) -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature | Status: new request | Priority: lowest | Milestone: Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple PartialTypeSignatures | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs class F a b | a -> b where foo :: a -- ... myFoo :: F a b => a myFoo = foo }}} Since ''b'' is not used and fully determined by ''a'' could the restriction on wildcards in constraints be lifted? {{{#!hs myFoo :: F a _ => a myFoo = foo }}} and eventually hiding it behind a type synonym: {{{#!hs type F' a = F a _ myFoo' :: F' a => a myFoo' = foo }}} I raised this issue at ICFP 2014, I haven't looked into whether dominique's response to [https://haskell- phabricator.global.ssl.fastly.net/D168#4818 my comment] applies. ---- I could achieve similar things with a type family but that work as I'd intended. ---- Or CPP :) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11641> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10775: Enable PolyKinds in GHC.Generics
by GHC 06 May '16

06 May '16

#10775: Enable PolyKinds in GHC.Generics -------------------------------------+------------------------------------- Reporter: | Owner: RyanGlScott | Type: feature | Status: new request | Priority: normal | Milestone: Component: | Version: 7.10.2 libraries/base | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- As suggested in [https://mail.haskell.org/pipermail/libraries/2015-July/025981.html this] Haskell libraries mailing list thread. Among other benefits, this would allow use of generic functions with `Proxy t` when `t` is of a kind other than `*`. There seem to be more changes required than just putting `{-# LANGUAGE PolyKinds #-}` in `GHC.Generics`, however, since I tried doing that myself and found myself unable to properly derive `Generic(1)` instances in `GHC.Generics`. Here is a snippet of the resulting error message: {{{ libraries/base/GHC/Generics.hs:826:1: error: Couldn't match type ‘M1 i0 c0 (M1 i1 c1 U1) p0’ with ‘M1 D x’ Expected type: Rep (Proxy t) x Actual type: M1 i0 c0 (M1 i1 c1 U1) p0 Relevant bindings include from :: Proxy t -> Rep (Proxy t) x (bound at libraries/base/GHC/Generics.hs:826:1) In the expression: M1 (M1 U1) In an equation for ‘from’: from Proxy = M1 (M1 U1) When typechecking the code for ‘from’ in a derived instance for ‘Generic (Proxy t)’: To see the code I am typechecking, use -ddump-deriv libraries/base/GHC/Generics.hs:826:1: error: Couldn't match type ‘M1 t0 t1 (M1 t3 t4 U1) t2’ with ‘M1 D x’ Expected type: Rep (Proxy t) x Actual type: M1 t0 t1 (M1 t3 t4 U1) t2 Relevant bindings include to :: Rep (Proxy t) x -> Proxy t (bound at libraries/base/GHC/Generics.hs:826:1) In the pattern: M1 (M1 U1) In an equation for ‘to’: to (M1 (M1 U1)) = Proxy When typechecking the code for ‘to’ in a derived instance for ‘Generic (Proxy t)’: To see the code I am typechecking, use -ddump-deriv In the instance declaration for ‘Generic (Proxy t)’ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10775> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11830: Disabling idle GC leads to freeze
by GHC 04 May '16

04 May '16

#11830: Disabling idle GC leads to freeze -------------------------------------+------------------------------------- Reporter: NeilMitchell | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Runtime | Version: 8.0.1-rc3 System | Keywords: | Operating System: Linux Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I'm currently getting a runtime freeze with a spinning CPU with the latest GHC 8.0.1 RC (8.0.0.20160411). Testing 2 months ago on whatever was the latest release candidate showed no problems. The reproduction steps are a bit long winded: * All tested on Ubuntu Linux. * Checkout Shake, https://github.com/ndmitchell/shake.git (currently at 75505baa5fc5d1b99a1162edae6ecf7669f00ed9). * {{{cabal install}}} * Checkout Ninja, https://github.com/ninja-build/ninja.git (currently at 78f548880e549c701bd77760e4b3f3a4ee147641). * Change to the {{{ninja}}} directory. * Run {{{./configure.py --bootstrap}}} * Run {{{cp ninja nin}}} * Run {{{./nin -t clean}}} * Run {{{shake}}} Observe that Shake fails to complete and starts spinning on 1 CPU. If you modify {{{shake.cabal}}} to remove {{{-with-rtsopts=-I0 -qg -qb}}} then it works again and completes in < 1 min. Adding back flags with {{{+RTS -I0 -RTS}}} shows that {{{-I0}}} alone is the culprit. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11830> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11999: expressing injectivity on functional dependencies gives orphan instances warnings
by GHC 04 May '16

04 May '16

#11999: expressing injectivity on functional dependencies gives orphan instances warnings -------------------------------------+------------------------------------- Reporter: dredozubov | 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: -------------------------------------+------------------------------------- Class.hs {{{ {-# LANGUAGE DataKinds, FlexibleInstances, FunctionalDependencies, KindSignatures, MultiParamTypeClasses, TypeFamilies #-} module Class where class C a b | a -> b, b -> a }}} Lib.hs {{{ {-# LANGUAGE DataKinds, FlexibleInstances, MultiParamTypeClasses, TypeFamilies #-} module Lib where import Class newtype Local = Local () instance C Local () }}} gives {{{ /Users/dr/workspace/broken-ophans-ghc/src/Lib.hs:10:1: warning: [-Worphans] Orphan instance: instance C Local () To avoid this move the instance declaration to the module of the class or of the type, or wrap the type with a newtype and declare the instance on the new type. }}} It seems weird to me and it is either a bug in the orphan instances checker or there is some fundamental aspect which i don't undestand. I've been able to reproduce this with 7.10.3 and 8-rc4. I've compiled a git repo with minimalistic example of this: [https://github.com/dredozubov/broken-instances-minimal] -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11999> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8865: Cannot derive well-kinded instance of form ‘Category
by GHC 02 May '16

02 May '16

#8865: Cannot derive well-kinded instance of form ‘Category ----------------------------+---------------------------------------------- Reporter: | Owner: adinapoli | Status: new Type: bug | Milestone: 7.8.1 Priority: normal | Version: 7.8.1-rc2 Component: Compiler | Operating System: MacOS X Keywords: | Type of failure: GHC rejects valid program Architecture: x86_64 | Test Case: (amd64) | Blocking: Difficulty: Unknown | Blocked By: | Related Tickets: | ----------------------------+---------------------------------------------- Hello everyone, sorry if this was already reported somewhere. I'm playing with GHC 7.8.1 RC2 and I'm updating hsenv to support GHC 7.8. This is a real code snippet, which was compiling fine in GHC 7.6.x {{{ newtype ArgArrow a b = ArgArrow (StaticArrowT KnownArgs (Kleisli (ReaderT Args IO)) a b) deriving (Category, Arrow, ArrowChoice) }}} but that yields the following in GHC 7.8.1-RC2 {{{ Cannot derive well-kinded instance of form ‘Category (ArgArrow ...)’ Class ‘Category’ expects an argument of kind ‘k -> k -> *’ In the newtype declaration for ‘ArgArrow’ }}} This might be related to the new feature of GHC 7.8, namely "kind variables" (you get the idea, even if the name is not 100% accurate). To make the code compile I had to enable {{{ StandaloneDeriving }}} and write the following: {{{ newtype ArgArrow a b = ArgArrow (StaticArrowT KnownArgs (Kleisli (ReaderT Args IO)) a b) deriving (Arrow, ArrowChoice) deriving instance Category ArgArrow }}} Is this by design or is a genuine bug? Thanks! Alfredo -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8865> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10266: Split base for Backpack
by GHC 02 May '16

02 May '16

#10266: Split base for Backpack -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: task | Status: new Priority: normal | Milestone: Component: | Version: 7.11 libraries/base | Operating System: Unknown/Multiple Keywords: backpack | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Let's resurrect #1338 and #1580. Our new concrete goal is to have users be able to replace 'base' with 'base-sig', which is some signature representing the modules from 'base' which we depend on. Since 'base' is a big, complicated package, the ability to specify subsets of 'base' is very useful: it can be used to define things like Haskell'98 base, base without any unsafe operations, etc. Right now, all wired in things live in ghc-prim (I believe). This is good, since we can't reasonably abstract wired in things away with a signature: GHC will always put them in some well-known place. However, this is not enough: there are many known-key/Rdr things the compiler knows about too, which need to be placed in specific package + module locations for GHC to be able to reference them; e.g. when deriving instances, etc. At the moment, most of these identifiers live in 'base', which is no good. So, here's the proposal: all non-rebindable GHC-known identifiers (as per PrelNames) should be moved to ghc-prim (or perhaps a new package? I don't really care either way) and reexported from the old packages which they were available from base. I'll try to work out in detail what moves, how to avoid orphan instances, etc. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10266> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11985: Core lint error on record syntax update/pattern synonym
by GHC 02 May '16

02 May '16

#11985: Core lint error on record syntax update/pattern synonym -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 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: -------------------------------------+------------------------------------- While on a flight I discovered some errors, if you load a file using record syntax for pattern synonyms: {{{#!hs module Foo where pattern Pair{x, y} = (x, y) }}} and load it with `-dcore-lint`: {{{ $ ghci -dcore-lint -ignore-dot-ghci -XPatternSynonyms /tmp/Foo.hs GHCi, version 8.1.20160419: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Foo ( /tmp/Foo.hs, interpreted ) Ok, modules loaded: Foo. *Foo> (1, 2) { x = 10 } *** Core Lint errors : in result of desugar expression *** [...] }}} full error message attached. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11985> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11983: Can't use IntPtr or WordPtr in a foreign import
by GHC 02 May '16

02 May '16

#11983: Can't use IntPtr or WordPtr in a foreign import -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: RyanGlScott Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.0.1 (FFI) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: #3008, #5529 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Despite the [http://hackage.haskell.org/package/base-4.8.2.0/docs/Foreign- Ptr.html#t:IntPtr docs claiming] that you can use `IntPtr` and `WordPtr` to convert to and from `intptr_t` and `uintptr_t`, you can't actually do so in a `foreign import` as of GHC 7.6. Here's a minimal example: {{{#!hs -- Example.hs {-# LANGUAGE ForeignFunctionInterface #-} module Example where {-# INCLUDE example.h #-} import Foreign.Ptr foreign import ccall "intptr_example" intPtrExample :: IntPtr -> IO () foreign import ccall "uintptr_example" wordPtrExample :: WordPtr -> IO () }}} {{{#!c // example.h #ifndef EXAMPLE_H #define EXAMPLE_H #include <stdint.h> void intptr_example(intptr_t); void uintptr_example(uintptr_t); #endif // EXAMPLE_H }}} {{{#!c // example.c #include <stdint.h> #include "example.h" void intptr_example(intptr_t i) {} void uintptr_example(uintptr_t u) {} }}} This appears to be a consequence of #3008, which prevents `newtype`s from being used as FFI types unless their constructors are exported. #5529 fixed this problem for the datatypes in `Foreign.C.Types` and `System.Posix.Types` by simply exporting their constructors, so I think all that's needed to fix this particular example is to export the constructors for `IntPtr` and `WordPtr`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11983> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11965: USE_PTHREAD_FOR_ITIMER causes unnecessary wake-ups
by GHC 02 May '16

02 May '16

#11965: USE_PTHREAD_FOR_ITIMER causes unnecessary wake-ups -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Runtime | Version: 7.10.3 System | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: #1623 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The `USE_PTHREAD_FOR_ITIMER` path appears to regress #1623 as it has no ability to disarm the timer when the ticker is in the `STOPPED` state. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11965> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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