#1965: Allow unconstrained existential contexts in newtypes -------------------------------------+------------------------------------- Reporter: guest | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 6.8.1 Resolution: | Keywords: 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 dfeuer): Replying to [comment:31 Iceland_jack]:
{{{#!hs data LanO j where LanO :: LanO (S i)
data LanS j where LanS :: Fin i -> LanS (S i) }}}
`Fin` defined as
Do `LanO`, `LanS` satisfy the conditions to be newtypes?
`LanO` does not, because its constructor takes no arguments. But that's perfectly fine; there's only one `LanO` value anyway. `LanS` does not either, because its constructor is lazy. If you wrote `LanS :: !(Fin i) -> LanS (S i)` then it would satisfy the conditions. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/1965#comment:33 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler