#7828: RebindableSyntax and Arrow ----------------------------------------------+---------------------------- Reporter: AlessandroVermeulen | Owner: Type: bug | jstolarek Priority: normal | Status: new Component: Compiler (Type checker) | Milestone: 7.10.1 Resolution: | Version: 7.6.2 Operating System: Unknown/Multiple | Keywords: Type of failure: GHC rejects valid program | Architecture: Test Case: | Unknown/Multiple Blocking: | Difficulty: Unknown | Blocked By: | Related Tickets: #1537, | #3613 ----------------------------------------------+---------------------------- Comment (by jstolarek): I have made some progress on this one today. I'm able to compile {{{ test :: Arrow a => a i i test = proc n -> do returnA -< n }}} using the new desugaring, which was not possible earlier. But I'm still stuck on this: {{{ test :: Arrow a => a i i test = proc n -> do returnA -< n returnA -< n }}} ie. desugaring of `thenA` although now I have gathered more information. With my new implementation the code above desugars to: {{{ (>>>) @ i @ (i, ()) @ i (arr @ i @ (i, ()) (\ (n :: i) -> (n, ()))) (thenA @ arrow @ i @ (GHC.Prim.Any *) @ (GHC.Prim.Any *) @ i $dArrow_auX ((>>>) @ (i, ()) @ i @ i (arr @ (i, ()) @ i (\ (ds2 :: (i, ())) -> case ds2 of _ { (ds4, ds5) -> ds4 })) (Control.Arrow.returnA @ arrow @ i $dArrow_auX)) ((>>>) @ (i, ()) @ i @ i (arr @ (i, ()) @ i (\ (ds2 :: (i, ())) -> case ds2 of _ { (ds4, ds5) -> ds4 })) (Control.Arrow.returnA @ arrow @ i $dArrow_auX))) }}} This looks correct except for the two `(GHC.Prim.Any *)` type parameters to `thenA`. One corresponds to the type of the stack, the other to result of first command (`b` in the type signature `a (e,s) b -> a (e,s) c -> a (e,s) c`). `thenA` should be polymorphic in these, but it seems that during typechecking I need to instantiate `s` and `b` to concrete values. I noticed that desugaring of `cmd` stored in the `BodyStmt` always passes `()` as the type of the stack. If this is correct then there's only the problem of what to do with `b`. Help needed here becuase I have no idea how to figure out the type of `b` from within `tcArrDoStmt`. Ross, I also tried to implement desugaring of `bind`. When generating the desugared Core for `cmd 'bind' \ p -> do { ss }` I have problem with the `\p ->` part. So, given the desugared `do { ss }`, `cmd` and the `bind` operator how should the generated command lambda look like? I'm still at a loss to undestand how to explicitly manipulate the stack from within Core. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7828#comment:42 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler