#15685: Pattern signature not inferred -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.6.1 Resolution: | Keywords: | PatternSynonyms Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones <simonpj@…>): In [changeset:"9ebfa03d9e9cbf79f698b5d4bd39e799e4e9a02c/ghc" 9ebfa03/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="9ebfa03d9e9cbf79f698b5d4bd39e799e4e9a02c" Fail fast on pattern synonyms We were recovering too eagerly from errors in pattern-synonym type inference, leading to a cascade of confusing follow up errors (Trac #15685, #15692). The underlying issue is that a pattern synonym should have a closed, fixed type, with no unification variables in it. But it wasn't! Fixing this made me change the interface to simplifyInfer slightly. Instead of /emitting/ a residual implication constraint, it now /returns/ it, so that the caller can decide what to do. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15685#comment:4> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler