#13594: Typechecker behavior w.r.t. BangPatterns and nested foralls has changed in 8.2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.2.1-rc2 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Gah! GHC has two sorts of bindings: `FunBind` and `PatBind`: * `FunBind` is used for function bindings, obviously, but also for bindings of form `x = e`. As the comments in `HsBinds.hs` say: {{{ -- FunBind is used for both functions @f x = e@ -- and variables @f = \x -> e@ -- -- Reason 1: Special case for type inference: see 'TcBinds.tcMonoBinds'. -- -- Reason 2: Instance decls can only have FunBinds, which is convenient. -- If you change this, you'll need to change e.g. rnMethodBinds }}} * `PatBind` is used for all other pattern bindings So `!x = e` is treated as a `PatBind`. And that means that it will take the `InferGen` patch (see `TcBinds.decideGeneralisationPlan`); and that means that it will behave differently type-inference-wise than `x = e; x :: sig`. And that is bad: bangs aren't supposed to affect typing. Best solution (I think): add a bang-flag to `FunRhs` (c.f. the `LexicalFixity` flag) in `HsExpr.HsMatchContext`. Then * `!x = e` would be a "simple" pattern binding * `FunBind` would handle all simple pattern bindings (as well as true function binding) NB: `(x) = e` would not be a "simple" pattern binding, and would still go via `PatBind`. Maybe that's even a feature. We could instead put the flag in `FunBind` itself, but I'm influenced by that `LexicalFixity` flag, which Alan migraed from `FunBind` to the `HsMatchContext` place (I forget why). I'm too swamped work on this, but I'll happily offer guidance. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13594#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13594: Typechecker behavior w.r.t. BangPatterns and nested foralls has changed in 8.2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.2.1-rc2 checker) | Keywords: BangPatterns, Resolution: | RankNTypes Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * owner: (none) => bgamari * priority: normal => high * milestone: => 8.2.1 Comment: I have a patch validating for this. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13594#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13594: Typechecker behavior w.r.t. BangPatterns and nested foralls has changed in 8.2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.2.1-rc2 checker) | Keywords: BangPatterns, Resolution: | RankNTypes Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): It is the `wip/T13594` branch but sadly validation failed. I'll need to look into why. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13594#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13594: Typechecker behavior w.r.t. BangPatterns and nested foralls has changed in 8.2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.2.1-rc2 checker) | Keywords: BangPatterns, Resolution: | RankNTypes Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Ben: can you put this on Phab? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13594#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13594: Typechecker behavior w.r.t. BangPatterns and nested foralls has changed in 8.2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.2.1-rc2 checker) | Keywords: BangPatterns, Resolution: | RankNTypes Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3525 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari ): In [changeset:"372995364c52eef15066132d7d1ea8b6760034e6/ghc" 37299536/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="372995364c52eef15066132d7d1ea8b6760034e6" Treat banged bindings as FunBinds This reworks the HsSyn representation to make banged variable patterns (e.g. !x = e) be represented as FunBinds instead of PatBinds, adding a flag to FunRhs to record the bang. Fixes #13594. Reviewers: austin, goldfire, alanz, simonpj Reviewed By: simonpj Subscribers: simonpj, rwbarton, thomie, mpickering Differential Revision: https://phabricator.haskell.org/D3525 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13594#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13594: Typechecker behavior w.r.t. BangPatterns and nested foralls has changed in 8.2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: bgamari Type: bug | Status: merge Priority: high | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.2.1-rc2 checker) | Keywords: BangPatterns, Resolution: | RankNTypes Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3525 Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Erm, the commit in 372995364c52eef15066132d7d1ea8b6760034e6 doesn't actually fix either of the programs I reported, does it? I get the same errors on a recent GHC HEAD build: {{{ $ inplace/bin/ghc-stage2 --interactive GHCi, version 8.3.20170511: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci λ> :set -XBangPatterns -XRankNTypes -XTypeFamilies λ> let x :: forall a . a ~ Integer => forall b. b ~ Integer => (a, b); !x = (1, 2) <interactive>:2:74: error: • Couldn't match expected type ‘forall b. b ~ Integer => (a, b)’ with actual type ‘(Integer, Integer)’ • In the expression: (1, 2) In a pattern binding: !x = (1, 2) • Relevant bindings include x :: forall b. b ~ Integer => (a, b) (bound at <interactive>:2:70) }}} {{{ $ inplace/bin/ghc-stage2 ../Bug.hs [1 of 1] Compiling Bug ( ../Bug.hs, ../Bug.o ) ../Bug.hs:6:1: error: Overloaded signature conflicts with monomorphism restriction x :: forall a. a ~ Integer => forall b. b ~ Integer => (a, b) | 6 | x :: forall a . a ~ Integer => forall b. b ~ Integer => (a, b) | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13594#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13594: Typechecker behavior w.r.t. BangPatterns and nested foralls has changed in 8.2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.2.1-rc2 checker) | Keywords: BangPatterns, Resolution: | RankNTypes Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3525 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari ): In [changeset:"3e79fe42b907653d97cd3a5496a8f133320354eb/ghc" 3e79fe42/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="3e79fe42b907653d97cd3a5496a8f133320354eb" Fix up tests for #13594 This adds the GHCi variant of the failing program in #13594. Also, I inadvertently changed the T13594 test previously introduced in a way that made it no longer faithfully test the ticket as written. Fix this. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13594#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13594: Typechecker behavior w.r.t. BangPatterns and nested foralls has changed in 8.2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.2.1-rc2 checker) | Keywords: BangPatterns, Resolution: | RankNTypes Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3525 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari ): In [changeset:"3032ae81dd14c2eaefa9ecd8880dafa9bda104d9/ghc" 3032ae81/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="3032ae81dd14c2eaefa9ecd8880dafa9bda104d9" Revert "Treat banged bindings as FunBinds" This partially reverts commit 372995364c52eef15066132d7d1ea8b6760034e6 as it doesn't actually fix #13594. Namely it does not revert the mkPrefixFunRhs refactoring since this is rather independent from the functional changes. Going to try again with a whole working patch }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13594#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13594: Typechecker behavior w.r.t. BangPatterns and nested foralls has changed in 8.2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: bgamari Type: bug | Status: patch Priority: high | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.2.1-rc2 checker) | Keywords: BangPatterns, Resolution: | RankNTypes Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3661 Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: new => patch * differential: Phab:D3525 => Phab:D3661 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13594#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13594: Typechecker behavior w.r.t. BangPatterns and nested foralls has changed in 8.2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: bgamari Type: bug | Status: merge Priority: high | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.2.1-rc2 checker) | Keywords: BangPatterns, Resolution: | RankNTypes Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3661 Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: patch => merge -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13594#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13594: Typechecker behavior w.r.t. BangPatterns and nested foralls has changed in 8.2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: bgamari Type: bug | Status: closed Priority: high | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.2.1-rc2 checker) | Keywords: BangPatterns, Resolution: fixed | RankNTypes Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3661 Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: merge => closed * resolution: => fixed Comment: Merged with c7ed911f1b102f85ba89fe2ccce9ecf8231d1b8c. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13594#comment:21 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13594: Typechecker behavior w.r.t. BangPatterns and nested foralls has changed in 8.2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: bgamari Type: bug | Status: closed Priority: high | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.2.1-rc2 checker) | Keywords: BangPatterns, Resolution: fixed | RankNTypes Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3661 Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): Furthermore, I thought top-level bangs were disallowed, regardless of types. The existence of a top-level bang causes an assertion failure in a debug compiler. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13594#comment:23 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13594: Typechecker behavior w.r.t. BangPatterns and nested foralls has changed in 8.2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: bgamari Type: bug | Status: closed Priority: high | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.2.1-rc2 checker) | Keywords: BangPatterns, Resolution: fixed | RankNTypes Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3661 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"af89d6872da2e00be738e1ac541346cd84e6d141/ghc" af89d68/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="af89d6872da2e00be738e1ac541346cd84e6d141" Reject top-level banged bindings Bizarrely, we were not rejecting !x = e Fix: * In the test in DsBinds.dsTopLHsBinds, use isBangedHsBind, not isBangedPatBind. (Indeed the latter dies altogther.) * Implement isBangedHsBind in HsUtils; be sure to handle AbsBinds All this was shown up by Trac #13594 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13594#comment:24 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler