#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 ryantrinkle): Hmm, when I try to convert it to a newtype, like this: {{{ newtype Some tag = forall t. This (tag t) }}} I get this error: {{{ src/Data/Some.hs:17:20: A newtype constructor cannot have existential type variables This :: forall (k :: BOX) (tag :: k -> *) (t :: k). tag t -> Some tag In the definition of data constructor ‘This’ In the newtype declaration for ‘Some’ }}} Is there a different way of converting it to a newtype that I'm overlooking? Here's a link to the original source of that Some: https://hackage.haskell.org/package/dependent-sum-0.3.2.1/docs/src/Data- Some.html#Some . The Hoogle output is more confusing to me than the original. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/1965#comment:25 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler