#14899: Significant compilation time regression between 8.4 and HEAD due to coverage checking -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.6.1 Component: Compiler | Version: 8.5 Resolution: | Keywords: | PatternMatchWarnings 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 bgamari): It seems to me like comment:4 (which I updated to fix a few mistakes) is only part of the story. In particular, the constraint `Δ'` proposed in that comment is not currently admitted under the constraint syntax given in the paper. In particular, the right hand size of a term equality (e.g. the `≈` production) is expected to be an expression. However, there is no way to lift `(u_0 |> sym co)` into an expression. More generally, it doesn't make sense to me to lift a value abstraction like `u_0` into an expression. Perhaps a new constraint variety is needed? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14899#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler