February 2018 - ghc-tickets

[GHC] #12514: Can't write unboxed sum type constructors in prefix form
by GHC 26 May '18

26 May '18

#12514: Can't write unboxed sum type constructors in prefix form -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 (Parser) | 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: -------------------------------------+------------------------------------- You can write `(# Int | Char #)`, but not `(# | #) Int Char`. This is annoying since it prevents you from partially applying unboxed sum type constructors, and it also precludes you from doing cool things like `reify ''(#||#)` (as I woefully noted [https://phabricator.haskell.org/D2448 here]). Luckily, I don't think fixing this would be too hard. The special case of parsing unboxed tuple type constructors as prefix is handled [http://git.haskell.org/ghc.git/blob/0d3bf62092de83375025edca6f7242812338542… here], so I //think// we'd just need to add a similar case for unboxed sums. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12514> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12451: TemplateHaskell and Data.Typeable - tcIfaceGlobal (local): not found
by GHC 26 May '18

26 May '18

#12451: TemplateHaskell and Data.Typeable - tcIfaceGlobal (local): not found -------------------------------------+------------------------------------- Reporter: mkloczko | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple TemplateHaskell, Typeable | Architecture: x86_64 | Type of failure: GHC rejects (amd64) | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following code produces an ghc panic error: {{{#!hs {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE ScopedTypeVariables #-} module TH where import Language.Haskell.TH import Language.Haskell.TH.Syntax import Data.Typeable usingType :: forall a. Typeable a => a -> Q [Dec] usingType _ = do -- Try to get anything using typeRep. let name = (tyConName $ typeRepTyCon $ typeRep (Proxy :: Proxy a)) `seq` "The name!" -- theF = "The name!" return [FunD (mkName "theF") [Clause [] (NormalB $ LitE $ StringL name ) []]] }}} {{{#!hs {-# LANGUAGE TemplateHaskell #-} module Main where import TH data A = A Int -- Changing the argument to (A 3) does not help. $(usingType (undefined :: A)) main = putStrLn $ theF }}} The error: {{{ ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-unknown-linux): tcIfaceGlobal (local): not found: $tcA [r5m0 :-> Type constructor ‘A’, r5m3 :-> Data constructor ‘A’, r5m9 :-> Identifier ‘A’] }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12451> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12452: TemplateHaskell - variables in top level splices and loading modules.
by GHC 26 May '18

26 May '18

#12452: TemplateHaskell - variables in top level splices and loading modules. -------------------------------------+------------------------------------- Reporter: mkloczko | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Linux TemplateHaskell | Architecture: x86_64 | Type of failure: GHC rejects (amd64) | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following code fails when loading Main module: {{{#!hs {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE ScopedTypeVariables #-} module TH where import Language.Haskell.TH import Language.Haskell.TH.Syntax import Data.Typeable usingType :: a -> Q [Dec] usingType _ = do let name = "The name!" -- theF = "The name!" return [FunD (mkName "theF") [Clause [] (NormalB $ LitE $ StringL name ) []]] }}} {{{#!hs {-# LANGUAGE TemplateHaskell #-} module Main where import TH data A = A Int -- Runs with `usingType (undefined :: A)` instead $(usingType (A 3) ) main = putStrLn $ theF }}} The error: {{{ $ ghc --make Main.hs [1 of 2] Compiling TH ( TH.hs, TH.o ) [2 of 2] Compiling Main ( Main.hs, Main.o ) attempting to use module ‘Main’ (Main.hs) which is not loaded }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12452> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13853: TypeApplications and record syntax don't mix
by GHC 26 May '18

26 May '18

#13853: TypeApplications and record syntax don't mix -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple TypeApplications | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Let's fire up GHCi: {{{ $ ~/Software/ghc-8.2.0.20170507/bin/ghci GHCi, version 8.2.0.20170507: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /Users/rscott/.ghci λ> :set -XTypeApplications -fprint-explicit-foralls λ> import Data.Functor.Identity }}} I can use `TypeApplications` on `Identity` like so: {{{ λ> Identity @Int 42 Identity 42 }}} But not if I try to use record syntax: {{{ λ> Identity @Int { runIdentity = 42 } <interactive>:4:15: error: parse error on input ‘{’ λ> (Identity @Int) { runIdentity = 42 } <interactive>:7:1: error: • Couldn't match expected type ‘Identity a0’ with actual type ‘Int -> Identity Int’ • In the expression: (Identity @Int) {runIdentity = 42} In an equation for ‘it’: it = (Identity @Int) {runIdentity = 42} }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13853> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12093: Wrong argument count in error message with TypeApplications
by GHC 26 May '18

26 May '18

#12093: Wrong argument count in error message with TypeApplications -------------------------------------+------------------------------------- Reporter: kwf | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | 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: -------------------------------------+------------------------------------- When I write: {{{#!hs {-# language TypeApplications #-} module Bug where wrong = id @Bool True False }}} I get the error: {{{ • Couldn't match expected type ‘Bool -> t’ with actual type ‘Bool’ • The function ‘id’ is applied to three arguments, but its type ‘Bool -> Bool’ has only one In the expression: id @Bool True False In an equation for ‘bad’: bad = id @Bool True False • Relevant bindings include bad :: t (bound at Bug.hs:8:1) }}} This seems to tell me that I ought to get rid of //two// of the arguments given to `id`, when in fact I only ought to remove //one//. In particular, the issue seems to be that GHC includes visibly applied type parameters in the count of "how many arguments is it applied to?" but does not include them in the count of "how many arguments does it have?" Suggested fix: in cases of this error with visible type application, report something akin to, "The function ‘id’ is applied to two type arguments and two value arguments, but its type has only one value argument." -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12093> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10778: GHC doesn't infer all constrains
by GHC 25 May '18

25 May '18

#10778: GHC doesn't infer all constrains -------------------------------------+------------------------------------- Reporter: danilo2 | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Hello! Let's consider following signatures: {{{ class (IndexOf a cont ~ idx, ElementByIdx idx cont ~ a, Measurable cont) => Container cont idx a class Container cont idx a => Appendable cont idx a class HasContainer a cont | a -> cont class Monad m => RefBuilder3 a m ref | a m -> ref where mkRef3 :: a -> m (ref a) }}} Now when I define following instance: {{{ instance (PtrFrom idx i, Appendable cont idx a, HasContainer g cont, Monad m) => RefBuilder3 a (GraphBuilderT g m) (Ptr i) where mkRef3 = undefined }}} I get an error: {{{ Illegal instance declaration for ‘RefBuilder3 a (GraphBuilderT g m) (Ptr i)’ The liberal coverage condition fails in class ‘RefBuilder3’ for functional dependency: ‘a m -> ref’ Reason: lhs types ‘a’, ‘GraphBuilderT g m’ do not jointly determine rhs type ‘Ptr i’ In the instance declaration for ‘RefBuilder3 a (GraphBuilderT g m) (Ptr i)’ }}} But when I add the constraint to the instance head: {{{ instance (PtrFrom idx i, Appendable cont idx a, HasContainer g cont, Monad m, IndexOf a cont ~ idx) => RefBuilder3 a (GraphBuilderT g m) (Ptr i) where mkRef3 a = fmap ptrFrom . withGraph . append $ a }}} It compiles fine. What's interesting, the constraint should be inferred by GHC, because we've got following funds here: {{{ g -> cont -- from HasContainer cont a -> idx -- from Appendable -> Container }}} Is this a GHC bug or am I missing something? If thats a bug, I will try to clean the code and make a minimal example. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10778> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10770: Typeable solver has strange effects
by GHC 25 May '18

25 May '18

#10770: Typeable solver has strange effects -------------------------------------+------------------------------------- Reporter: | Owner: NeilMitchell | Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Given: {{{#!hs import Data.Typeable main = print $ foo $ Just () foo :: Typeable (t a) => t a -> String foo x = let k = show $ typeOf x in k }}} I get: {{{ TypeableInfer.hs:7:24: Could not deduce (Typeable t) arising from a use of `typeOf' from the context (Typeable (t a)) bound by the type signature for foo :: Typeable (t a) => t a -> String at TypeableInfer.hs:6:8-38 In the second argument of `($)', namely `typeOf x' In the expression: show $ typeOf x In an equation for `k': k = show $ typeOf x }}} However, the error goes away with the minor modification of: {{{#!hs foo x = show $ typeOf x }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10770> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14857: GHC-8.4.1 release notes don't mention 'Div', 'Mod' and other type families
by GHC 25 May '18

25 May '18

#14857: GHC-8.4.1 release notes don't mention 'Div', 'Mod' and other type families -------------------------------------+------------------------------------- Reporter: chshersh | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Documentation | Version: 8.4.1-alpha3 Keywords: | Operating System: Unknown/Multiple base,documentation,div,mod,type | families,changelog,release notes | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- GHC 8.4.1 brought support for `Div`, `Mod` and `Log2` type families for type level natural numbers: * https://downloads.haskell.org/~ghc/master/libraries/base/base/GHC- TypeNats.html#t:Div I'm actually using this feature in `o-clock` package * https://github.com/serokell/o-clock But I was told about this feature only by other Haskell developer. And I don't see this change described in release notes for GHC 8.4.1: * https://downloads.haskell.org/%7Eghc/master/users-guide/8.4.1-notes.html #base-library -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14857> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10490: Missing binder type check in coercion equality test?
by GHC 25 May '18

25 May '18

#10490: Missing binder type check in coercion equality test? -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 (Type checker) | Operating System: Unknown/Multiple Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- I was reading the equality testing code for coercions and I noticed this line: {{{ coreEqCoercion2 env (ForAllCo v1 co1) (ForAllCo v2 co2) = coreEqCoercion2 (rnBndr2 env v1 v2) co1 co2 }}} This doesn't test if the types of the binders are equal. Should it? (Or is the type always trivially the same?) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10490> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9587: Type checking with type functions introduces many type variables, which remain ambiguous. The code no longer type checks.
by GHC 25 May '18

25 May '18

#9587: Type checking with type functions introduces many type variables, which remain ambiguous. The code no longer type checks. -------------------------------------+------------------------------------- Reporter: oleg | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.3 checker) | Operating System: Keywords: type family, | Unknown/Multiple ambiguity check | Type of failure: GHC Architecture: Unknown/Multiple | rejects valid program Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Before the type ambiguity check was introduced, I could write the following code {{{ {-# LANGUAGE NoMonomorphismRestriction #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE ScopedTypeVariables #-} -- {-# LANGUAGE AllowAmbiguousTypes #-} module T where type family Arr (repr :: * -> *) (a :: *) (b :: *) :: * class ESymantics repr where int :: Int -> repr Int add :: repr Int -> repr Int -> repr Int lam :: (repr a -> repr b) -> repr (Arr repr a b) app :: repr (Arr repr a b) -> repr a -> repr b {- te4 :: (Arr repr (Arr repr Int Int) (Arr repr Int Int) ~ Arr repr (Arr repr Int Int) (Arr repr Int b), ESymantics repr) => repr b -} te4 = let c3 = lam (\f -> lam (\x -> f `app` (f `app` (f `app` x)))) in (c3 `app` (lam (\x -> x `add` int 14))) `app` (int 0) -- t = lam (\f -> f `app` int 0) newtype R a = R{unR :: a} type instance Arr R a b = a -> b instance ESymantics R where int = R add (R x) (R y) = R $ x + y lam f = R $ unR . f . R app (R f) (R x) = R $ f x tR = unR te4 }}} (This is a simple code abstracted from a longer code that for sure worked in 2010: I showed it in a SSGIP lecture at Oxford.) The inferred type of te4 is shown in comments. The type is not ideal but the best what can be done under circumstances. In tR, repr is instantiated to R and the type function Arr can finally be applied and the equality constraint resolved. Since then, the type inference has changed and the code no longer type checks: {{{ Could not deduce (Arr repr (Arr repr a0 b0) (Arr repr a2 b0) ~ Arr repr (Arr repr a b) (Arr repr a4 b)) from the context (ESymantics repr, Arr repr a4 a3 ~ Arr repr a b, Arr repr a3 a ~ Arr repr a b) bound by the inferred type for ‘c3’: (ESymantics repr, Arr repr a4 a3 ~ Arr repr a b, Arr repr a3 a ~ Arr repr a b) => repr (Arr repr (Arr repr a b) (Arr repr a4 b)) }}} What is worse, there does not appear to be *any* way to get the code to type check. No amount of type annotations helps. The code has to be dramatically re-written, or just given up. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9587> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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