#9739: GHC 7.8 chokes on recursive classes -------------------------------------+------------------------------------- Reporter: bitonic | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 (Type checker) | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Changes (by ezyang): * version: 7.8.3 => 7.9 Comment: Confirmed to loop on GHC HEAD 75979f3661ff16ec44528a23005ac1be2b9683fe -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9739#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9739: GHC 7.8 chokes on recursive classes -------------------------------------+------------------------------------- Reporter: bitonic | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 (Type checker) | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: Compile- | Related Tickets: time crash | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by bitonic): Actually, you don't need `MultiParamTypeClasses`: {{{#!hs module Foo where class Class3 a => Class1 a where class Class2 a where class2 :: (Class3 a) => b class (Class1 a, Class2 a) => Class3 a where }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9739#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9739: GHC 7.8 chokes on recursive classes -------------------------------------+------------------------------------- Reporter: bitonic | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 7.9 (Type checker) | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: Compile- | Related Tickets: time crash | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Changes (by dfeuer): * milestone: => 7.10.1 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9739#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9739: GHC 7.8 chokes on recursive classes -------------------------------------+------------------------------------- Reporter: bitonic | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 7.9 (Type checker) | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: Compile- | Related Tickets: time crash | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by dfeuer): This is interesting: the definition of `Class1` is actually ''illegal'' in Haskell 98, because `class3` constrains the type variable `a`. This sort of thing is only supposed to be allowed with `-XConstrainedClassMethods`. In fact, if you enable that flag, suddenly the compiler realizes there's a loop! So it looks likely that someone made the flag enable the extra loop checking required by such methods, but accidentally failed to make it control whether such things are allowed at all! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9739#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9739: GHC 7.8 chokes on recursive classes -------------------------------------+------------------------------------- Reporter: bitonic | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 7.9 (Type checker) | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: Compile- | Related Tickets: time crash | Test Case: | typecheck/should_fail/T9739 | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by dfeuer): I don't understand why such a member signature was even allowed without `-XConstrainedClassMethods`. That's essentially a syntax error! Someone also noticed that `Foldable` members currently have a redundant (but harmless) `Foldable` constraint that I think shouldn't have been allowed (I'll take care of those). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9739#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9739: GHC 7.8 chokes on recursive classes -------------------------------------+------------------------------------- Reporter: bitonic | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 7.9 (Type checker) | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: Compile- | Related Tickets: time crash | Test Case: | typecheck/should_fail/T9739 | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"7c79633688238086ad60e1d23e0a424bb4eb325f/ghc"]: {{{ #!CommitTicketReference repository="ghc" revision="7c79633688238086ad60e1d23e0a424bb4eb325f" Fix the superclass-cycle detection code (Trac #9739) We were falling into an infinite loop when doing the ambiguity check on a class method, even though we had previously detected a superclass cycle. There was code to deal with this, but it wasn't right. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9739#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9739: GHC 7.8 chokes on recursive classes -------------------------------------+------------------------------------- Reporter: bitonic | Owner: Type: bug | Status: closed Priority: normal | Milestone: 7.10.1 Component: Compiler (Type | Version: 7.9 checker) | Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Compile-time | Test Case: crash | typecheck/should_fail/T9739 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): -------------------------------------+------------------------------------- Comment (by Matthew Pickering ): In [changeset:"44640af7afa1a01ff2e2357f7c1436b4804866fc/ghc" 44640af7/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="44640af7afa1a01ff2e2357f7c1436b4804866fc" Allow as-patterns in pattern synonym declarations. We can allow them if they contain no free variables. This patch just allows them in one direction and not to be used as builders as the original ticket suggests. Test Plan: ./validate Reviewers: austin, bgamari Reviewed By: bgamari Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D1666 GHC Trac Issues:  #9739 Conflicts: testsuite/tests/patsyn/should_fail/all.T }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9739#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler