March 2016 - ghc-tickets

[GHC] #10181: Lint check: arity invariant
by GHC 11 May '16

11 May '16

#10181: Lint check: arity invariant -------------------------------------+------------------------------------- Reporter: nomeata | Owner: nomeata Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- The Arity of an ID should not exceed the arity of its type, nor the arity of its strictness signature, if it is a bottoming signatures. This should be checked by a lint check (suggested by SPJ in https://phabricator.haskell.org/D747?id=2498#inline-6058) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10181> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11746: I encountered an: internal error: evacuate: strange closure type 803645000
by GHC 11 May '16

11 May '16

#11746: I encountered an: internal error: evacuate: strange closure type 803645000 --------------------------------------+------------------------------- Reporter: hkBst | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Keywords: | Operating System: Linux Architecture: x86_64 (amd64) | Type of failure: GHCi crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: --------------------------------------+------------------------------- I encountered an: internal error: evacuate: strange closure type 803645000 after loading and running the attached code under GHCi. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11746> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9478: Partial type signatures
by GHC 10 May '16

10 May '16

#9478: Partial type signatures -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: Phab:D168 -------------------------------------+------------------------------------- This ticket tracks progress on '''partial type signatures'''. * Wiki page [wiki:PartialTypeSignatures] * Phabricator link: Phab:D168 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9478> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11432: Cannot export operator newtype
by GHC 10 May '16

10 May '16

#11432: Cannot export operator newtype -------------------------------------+------------------------------------- Reporter: phadej | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1-rc1 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 TypeOperators #-} module Main (main, (-.->)(..)) where main :: IO () main = return () newtype (f -.-> g) a = Fn { apFn :: f a -> g a } }}} Fails to compile with {{{ [1 of 1] Compiling Main ( fn.hs, interpreted ) fn.hs:2:20: error: Not in scope: ‘-.->’ fn.hs:2:20: error: The export item ‘(-.->)(..)’ attempts to export constructors or class methods that are not visible here }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11432> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11692: Suggest default definition of Applicative
by GHC 07 May '16

07 May '16

#11692: Suggest default definition of Applicative -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: GHCi | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs ghci> data A a = A a deriving (Show, Functor) ghci> instance Monad A <interactive>:3:10: error: • No instance for (Applicative A) arising from the superclasses of an instance declaration • In the instance declaration for ‘Monad A’ }}} could suggest defining it in terms of `Monad`: {{{#!hs <interactive>:3:10: error: • No instance for (Applicative A) arising from the superclasses of an instance declaration • In the instance declaration for ‘Monad A’ • Default implementation given a `Monad` instance: instance Applicative A where pure = return (<*>) = Control.Monad.ap }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11692> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[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] #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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