June 2017 - ghc-tickets

[GHC] #12420: Users guide link for hsc2hs has bitrotten
by GHC 14 Sep '18

14 Sep '18

#12420: Users guide link for hsc2hs has bitrotten -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: task | Status: new Priority: normal | Milestone: Component: hsc2hs | 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: -------------------------------------+------------------------------------- https://hackage.haskell.org/package/hsc2hs links to http://www.haskell.org/ghc/docs/latest/html/users_guide/hsc2hs.html which is dead. I think https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/utils.html #writing-haskell-interfaces-to-c-code-hsc2hs is what is desired. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12420> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11197: Overeager deferred type errors
by GHC 11 Sep '18

11 Sep '18

#11197: Overeager deferred type errors -------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: 8.0.1 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: -------------------------------------+------------------------------------- With `TypeInType`, the solver now works in terms of unlifted equality. The only place this matters is in deferred type errors, which now are more eager than they were before. For example: {{{ {-# OPTIONS_GHC -fdefer-type-errors #-} module Main where main = do putStrLn "Hi there." putStrLn True }}} This used to print {{{ Hi there. Defer: Defer.hs:7:12: error: ... }}} Now it prints {{{ Defer: Defer.hs:7:12: error: ... }}} No more `Hi there.`. Thinking about Core, this change should be expected. GHC puts all evidence bindings for `main` at the top, and with unlifted equality in the solver, these bindings now contain `case typeError ... of ...`, which forces the type error eagerly. Previously, there was a lazy binding for a lifted equality witness, unpacked only at the last moment by magic in the desugarer, thus the lazier warning. Simon has proposed customizing the !FloatIn pass to deal with this scenario. I do believe this would work nicely, but I have not yet implemented it. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11197> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12833: GHCi
by GHC 11 Sep '18

11 Sep '18

#12833: GHCi -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature | Status: new request | 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: -------------------------------------+------------------------------------- In multiline mode you can define a multi-line Haskell function: {{{ Prelude> :set +m Prelude> let Prelude| f :: Int -> Int Prelude| f 0 = 0 Prelude| f n = n - 1 Prelude| Prelude> }}} Is there a reason why it couldn't work with other things like {{{ Prelude> :set -XPatternSynonyms Prelude> let Prelude| pattern A = 'A' Prelude| <interactive>:27:1: error: Illegal pattern synonym declaration for ‘A’ Pattern synonym declarations are only valid at top level }}} {{{ Prelude> let Prelude| data A Prelude| = B Prelude| | C Int Prelude| <interactive>:30:1: error: parse error (possibly incorrect indentation or mismatched brackets) }}} {{{ Prelude> let Prelude| type A = Int Prelude| <interactive>:48:1: error: parse error (possibly incorrect indentation or mismatched brackets) }}} couldn't work, similar to how they work with `:{` and `:}`: {{{ Prelude> :{ Prelude| data A Prelude| = B Prelude| | C Int Prelude| :} Prelude> }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12833> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12578: Update links to SPJ’s papers
by GHC 09 Sep '18

09 Sep '18

#12578: Update links to SPJ’s papers -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: task | Status: new Priority: normal | Milestone: 8.2.1 Component: Documentation | 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: -------------------------------------+------------------------------------- It seems that Simon’s homepage got restructured, and a lot of links in the documentation and the code comments are not valid any more. At least these need to be looked at: {{{ $ git grep 'people/simonpj' compiler/types/FamInstEnv.hs:http://research.microsoft.com/en- us/um/people/simonpj/papers/ext-f/axioms-extended.pdf compiler/types/Unify.hs:[1]: http://research.microsoft.com/en- us/um/people/simonpj/papers/ext-f/axioms-extended.pdf docs/core-spec/core-spec.mng:phantom equality includes all types. See \url{http://ghc.haskell.org/trac/ghc/wiki/Roles} and \url{http://research.microsoft.com/en- us/um/people/simonpj/papers/ext-f/coercible.pdf} docs/users_guide/glasgow_exts.rst:paper <http://research.microsoft.com/en- us/um/people/simonpj/papers/ext-f/>`__. docs/users_guide/glasgow_exts.rst:cloud <http://research.microsoft.com/en- us/um/people/simonpj/papers/parallel/remote.pdf>`__, docs/users_guide/using-optimisation.rst: multiprocessor <http://research.microsoft.com/en- us/um/people/simonpj/papers/parallel/>`__. docs/users_guide/using-optimisation.rst: (ICFP'96) <http://research.microsoft.com/en- us/um/people/simonpj/papers/float.ps.gz>`__. docs/users_guide/using-optimisation.rst: (ICFP'96) <http://research.microsoft.com/en- us/um/people/simonpj/papers/float.ps.gz>`__. docs/users_guide/using-optimisation.rst: programs <http://research.microsoft.com/en-us/um/people/simonpj/papers/spec- constr/index.htm>`__. docs/users_guide/using-optimisation.rst: thesis <http://research.microsoft.com/en-us/um/people/simonpj/papers/santos- thesis.ps.gz>`__ docs/users_guide/using-optimisation.rst: analyser <http://research.microsoft.com/en-us/um/people/simonpj/papers/simple- strictnes-analyser.ps.gz>`__, libraries/base/GHC/Arr.hs:-- http://research.microsoft.com/en- us/um/people/simonpj/papers/ext-f/coercible.pdf libraries/base/GHC/Base.hs:-- http://research.microsoft.com/en- us/um/people/simonpj/papers/ext-f/coercible.pdf testsuite/tests/dependent/should_compile/all.T:# http://research.microsoft.com/en-us/um/people/simonpj/papers/haskell- dynamic/ $ git grep '~simonpj' compiler/coreSyn/CoreSyn.hs:-- GHC uses System FC <http://research.microsoft.com/~simonpj/papers/ext-f/> for this purpose, docs/users_guide/bugs.rst: inliner <http://research.microsoft.com/~simonpj/Papers/inlining/>`__. docs/users_guide/glasgow_exts.rst: Languages <http://research.microsoft.com/~simonpj/Papers/slpj-book-1987/>`__. docs/users_guide/glasgow_exts.rst:"group by" <http://research.microsoft.com/~simonpj/papers/list-comp>`__, docs/users_guide/glasgow_exts.rst:space <http://research.microsoft.com/~simonpj/Papers/type-class-design- space/>`__ docs/users_guide/glasgow_exts.rst:papers <http://research.microsoft.com/~simonpj/papers/constraints/index.htm>`__ docs/users_guide/glasgow_exts.rst:Haskell <http://research.microsoft.com/~simonpj/papers/meta-haskell/>`__" docs/users_guide/glasgow_exts.rst:2 <http://research.microsoft.com/~simonpj/papers/meta-haskell/notes2.ps>`__. libraries/base/Control/Concurrent/MVar.hs:-- <http://research.microsoft.com/~simonpj/papers/concurrent-haskell.ps.gz "Concurrent Haskell"> libraries/base/GHC/Conc/Sync.hs:(<http://research.microsoft.com/~simonpj/Papers /asynch-exns.htm>). }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12578> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10827: GHCi should support interpeting multiple packages/units with separate DynFlags
by GHC 08 Sep '18

08 Sep '18

#10827: GHCi should support interpeting multiple packages/units with separate DynFlags -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: GHC API | Version: 7.11 Keywords: backpack | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Stack and other tools are attempting to make the user-experience of developing multiple packages simultaneously better. Thus, if you have source packages p, q and r (which all depend on them), `stack build` builds all of them. They are quite interested in support `stack ghci` but there are problems: https://github.com/commercialhaskell/stack/issues/665 The essence of the problem is twofold: 1. If you ask GHCi to interpret modules from multiple packages (e.g. by having multiple source directories), GHCi currently only knows how to put all of them into the same home package. This will fail if two packages have a module with the same name; also, modules in the other packages will always see modules (even if they're supposed to be hidden). 2. A GHCi session only has one global set of dynamic flags, but each package may be compiled with its own set of DynFlags (e.g. package global LANGUAGE pragmas). This means the "default DynFlags" needs to be varied between packages. It's not too obvious to me how to fix (1) (at least, you'd have to make the HPT support sets of HomeModInfos from multiple packages), but (2) seems tractable: since we already track DynFlags on a per-module basis, we just have to arrange for a "package" level DynFlag to be applied to the correct ModSummarys. Similar functionality would be useful for Backpack. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10827> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12356: StaticPointers support in GHCi
by GHC 07 Sep '18

07 Sep '18

#12356: StaticPointers support in GHCi -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: feature | Status: new request | Priority: normal | Milestone: 8.2.1 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: #12000 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Currently GHCi does not support `-XStaticPointers`, which is quite annoying for those of us who actually use `-XStaticPointers` in day-to-day development. It would be great if GHCi could grow support for this extension. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12356> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9622: GHCi command to solve a constraint
by GHC 07 Sep '18

07 Sep '18

#9622: GHCi command to solve a constraint -------------------------------------+------------------------------------- Reporter: monoidal | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.3 checker) | Operating System: Keywords: | Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: Difficulty: Unknown | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- It would be nice to have a `:solve` command for ghci that took a class constraint and returned either its derivation or an error message. A possible interface could look like so: {{{ ghci> :solve Eq (Maybe Type1, Bool) 1) instance Eq Type1 -- Defined in ‘MyModule’ 2) instance Eq a => Eq (Maybe a) -- Defined in ‘GHC.Classes’ 3) instance Eq (Maybe Type1) -- Put a ~ Int in 2) and use 1) 4) instance Eq Bool -- Defined in ‘GHC.Classes’ 5) instance (Eq a, Eq b) => Eq (a,b) -- Defined in ‘GHC.Classes’ 6) instance Eq (Maybe Type1, Bool) -- Put a ~ Maybe Type1, b ~ Bool in 5) and use 3), 4) ghci> :solve Eq (Int -> Int) No instance for Eq (Int -> Int) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9622> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13499: "Panic: no skolem info" with StaticPointers and typed hole
by GHC 06 Sep '18

06 Sep '18

#13499: "Panic: no skolem info" with StaticPointers and typed hole -------------------------------------+------------------------------------- Reporter: Otini | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Linux StaticPointers, hole, skolem, | panic | Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When compiling this minimal example: {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE StaticPointers #-} import Data.Typeable (Typeable) import GHC.StaticPtr (StaticPtr) f :: Typeable a => StaticPtr (a -> a) f = static (\a -> _) main :: IO () main = return () }}} I get this output: {{{ Bug.hs:8:19: error:ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-unknown-linux): No skolem info: a_aJo[sk] Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} Unlike similar reported bugs, this happens on both 8.0.1 and 8.0.2. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13499> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10249: Suboptimal error message with deferred type errors
by GHC 05 Sep '18

05 Sep '18

#10249: Suboptimal error message with deferred type errors -------------------------------------+------------------------------------- Reporter: | Owner: Iceland_jack | Status: new Type: feature | Milestone: request | Version: 7.10.1 Priority: normal | Operating System: Unknown/Multiple Component: GHCi | Type of failure: None/Unknown Keywords: | Blocked By: Architecture: | Related Tickets: Unknown/Multiple | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- {{{#!hs $ ghci -fdefer-type-errors -ignore-dot-ghci GHCi, version 7.10.0.20150316: http://www.haskell.org/ghc/ :? for help Prelude> _ <interactive>:2:1: Warning: Found hole ‘_’ with type: IO t0 Where: ‘t0’ is an ambiguous type variable In the first argument of ‘GHC.GHCi.ghciStepIO :: IO a_aly -> IO a_aly’, namely ‘_’ In a stmt of an interactive GHCi command: it <- GHC.GHCi.ghciStepIO :: IO a_aly -> IO a_aly _ *** Exception: <interactive>:2:1: Found hole ‘_’ with type: IO t0 Where: ‘t0’ is an ambiguous type variable In the first argument of ‘GHC.GHCi.ghciStepIO :: IO a_aly -> IO a_aly’, namely ‘_’ In a stmt of an interactive GHCi command: it <- GHC.GHCi.ghciStepIO :: IO a_aly -> IO a_aly _ (deferred type error) Prelude> }}} It should ideally not expose `ghciStepIO` to the user. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10249> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10756: Allow users to indicate inaccessible patterns
by GHC 05 Sep '18

05 Sep '18

#10756: Allow users to indicate inaccessible patterns -------------------------------------+------------------------------------- Reporter: edsko | Owner: Type: feature | Status: new request | 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: | -------------------------------------+------------------------------------- Consider {{{#!hs {-# LANGUAGE KindSignatures #-} {-# LANGUAGE GADTs #-} data Elem :: * -> * -> * where EZ :: Elem (f , fs) f ES :: Elem fs f -> Elem (f', fs) f elemAbsurd :: Elem () f -> a elemAbsurd _ = error "inaccessible" }}} This catch-all in `elemAbsurd` is very unfortunate, because if I change my datatype and not all cases are inaccessible anymore the type checker will not be warning me. Although of course there is recent work by SPJ et al on inferring more inaccessible cases, I think it would be tremendously useful for users to be able to indicate that patterns are in fact inaccesible. I'd be very happy if I could write {{{#!hs elemAbsurd :: Elem () f -> a elemAbsurd EZ = inaccessible elemAbsurd (ES _) = inaccessible }}} Note that ghc ''can already detect that these patterns are in fact inaccessible'': it won't let me write the above: {{{ T.hs:12:12: Couldn't match type ‘()’ with ‘(f, fs)’ Inaccessible code in a pattern with constructor EZ :: forall f fs. Elem (f, fs) f, in an equation for ‘elemAbsurd’ }}} So I think it should be very very simple to change the type checker to allow to write cases like this if and only if the RHS is a specially designated symbol "inaccessible", which could be defined simply as {{{#!hs inaccessible :: a inaccessible = error "inaccessible" }}} in `GHC.Prim` or something. This would seem like very little work, and a correspondingly tiny patch, but with quite a large payoff. Future work in automatically detecting inaccessible cases would not make existing code using this style wrong, it just means that we have to write fewer inaccessible cases by hand; but even with more sophisticated inference algorithms for inaccessible cases there will still be inaccessible cases remaining. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10756> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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