#14386: GHC doesn't allow Coercion between partly-saturated type constructors -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 Resolution: | Keywords: roles 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 nomeata): Maybe not quite intentional, but certainly expected. I think the coercion you want is not even expressible at the level of Core, because the newtype gives you the axiom {{{ forall cat a b. Op cat a b ~R cat b a }}} And as you can see you can only use this axiom once `Op` has all three arguments. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14386#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler