#9352: Allow `State# s` argument/result types in `ccall` FFI imports -------------------------------------+------------------------------------- Reporter: hvr | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.2 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #9281, #11032 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): The behavior observed by hvr in comment:7 is (was?) in fact intentional. It is documented in this note in `TyType`, {{{ Note [Marshalling void] ~~~~~~~~~~~~~~~~~~~~~~~ We don't treat State# (whose PrimRep is VoidRep) as marshalable. In turn that means you can't write foreign import foo :: Int -> State# RealWorld Reason: the back end falls over with panic "primRepHint:VoidRep"; and there is no compelling reason to permit it }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9352#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler