#9867: PatternSynonyms + ScopedTypeVariables triggers an internal error -------------------------------------+------------------------------------- Reporter: antalsz | Owner: cactus Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Resolution: | Keywords: Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by cactus): Hrm. So what's happening here is that when we see {{{ pattern Nil = [] :: [a] }}} we rename and typecheck `[] :: [a]` as a pattern (like in a function definition); this by itself requires `ScopedTypeVariables` (in `rnHsBndrSig` I believe), as you can see by trying the following: {{{ {-# LANGUAGE PatternSynonyms #-} pattern Nil = [] :: [a] }}} {{{ T9867a.hs:2:21: Illegal type signature: ‘[a]’ Perhaps you intended to use ScopedTypeVariables In a pattern type-signature }}} If you do turn on `ScopedTypeVariables`, renaming succeeds and puts an unbound type variable in the type signature: {{{ pattern main@main:Main.Nil{d rvh} = ghc-prim-0.3.1.0:GHC.Types.[]{(w) d 6m} :: [a{tv awt}] }}} Then `tcInferPatSynDecl` typechecks this right-hand side, via some indirections: {{{ T9867.hs:2:15: env2 [(a{tv awt}, Type variable ‘a{tv awt}’ = a{tv aww}[sig:2])] T9867.hs:2:9: Skolemising a{tv aww}[sig:2] := a{tv awx}[sk] T9867.hs:2:9: writeMetaTyVar a{tv aww}[sig:2] := a{tv awx}[sk] }}} but by the time we get to `tc_patsyn_finish`, both `a{tv aww}` and `a{tv awx}` show up, as two separate types: the pattern type is `[a{tv awx}]`, but the pattern definition is `[] :: [a{tv aww}]`, so we end up generating the following code for the matcher: {{{ main@main:Main.$mNil{v rws}[gid] :: forall (r{tv awy}[sk] :: ghc-prim-0.3.1.0:GHC.Prim.OpenKind{(w) tc 34g}) a{tv awx}[sk]. [a{tv awx}[sk]] -> (ghc-prim-0.3.1.0:GHC.Prim.Void#{(w) tc 32L} -> r{tv awy}[sk]) -> (ghc-prim-0.3.1.0:GHC.Prim.Void#{(w) tc 32L} -> r{tv awy}[sk]) -> r{tv awy}[sk] [GblId, Str=DmdType] main@main:Main.$mNil{v rws} = /\(@ (r{tv awy}[sk] :: ghc-prim-0.3.1.0:GHC.Prim.OpenKind{(w) tc 34g})). /\(@ a{tv awx}[sk]). \ ((scrut_awA{v}[lid] :: [a{tv awx}[sk]])) ((cont_awB{v}[lid] :: Void#{(w) tc 32L} -> r{tv awy}[sk])) ((fail_awC{v}[lid] :: Void#{(w) tc 32L} -> r{tv awy}[sk])) -> case scrut_awA{v} of { ghc-prim-0.3.1.0:GHC.Types.[]{(w) d 6m}{EvBinds{}} :: [a{tv aww}[sig:2]] -> cont_awB{v} ghc-prim-0.3.1.0:GHC.Prim.void#{(w) v 0l} _ -> fail_awC{v} ghc-prim-0.3.1.0:GHC.Prim.void#{(w) v 0l} } }}} (note how we still have `[a{tv aww}]` in the type annotation of the case branch). This is where the error message is coming from. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9867#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9867: PatternSynonyms + ScopedTypeVariables triggers an internal error -------------------------------------+------------------------------------- Reporter: antalsz | Owner: cactus Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 (Type checker) | Keywords: pattern synonyms 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 cactus): * keywords: => pattern synonyms * failure: None/Unknown => Compile-time crash * component: Compiler => Compiler (Type checker) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9867#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9867: PatternSynonyms + ScopedTypeVariables triggers an internal error -------------------------------------+------------------------------------- Reporter: antalsz | Owner: cactus Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 (Type checker) | Keywords: PatternSynonyms 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 cactus): * keywords: pattern synonyms => PatternSynonyms -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9867#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9867: PatternSynonyms + ScopedTypeVariables triggers an internal error -------------------------------------+------------------------------------- Reporter: antalsz | Owner: cactus Type: bug | Status: merge Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.3 checker) | Keywords: Resolution: | PatternSynonyms Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash | Test Case: Blocked By: | patsyn/should_compile/T9867 Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by simonpj): * status: new => merge * testcase: => patsyn/should_compile/T9867 Comment: Fixed by {{{ commit 3ea40e38a7ae03c05cb79485fb04a3f00c632793 Author: Simon Peyton Jones Date: Mon Jan 19 09:06:21 2015 +0000 Fix the 'builder' code for pattern synonyms with type signatures See Note [Type signatures and the builder expression] for the details compiler/typecheck/TcPatSyn.hs | 144 ++++++++++++++++++++++------------------ 1 file changed, 79 insertions(+), 65 deletions(-) }}} and follow up wibble {{{ commit 9a1458266b8fa349c9fb58889825d899a762fa27 Author: Simon Peyton Jones Date: Mon Jan 19 10:20:39 2015 +0000 Add missing argument in Match, a merge bug (apologies) compiler/typecheck/TcPatSyn.hs | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) }}} We could consider merging this to 7.10. It isn't huge, but let's do it if it's easy. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9867#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler