#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): Simon, I think I need some help with typechecking. I defined `thenA` (Ross' `bind_`) to have the type `Arrow a => a (e,s) b -> a (e,s) c -> a (e,s) c`. Now I'm trying to typecheck `thenA` operator stored inside `BodyStmtA` constructor (a new arrow equivalent of monadic `BodyStmt`). I wrote something like this: {{{ tcArrDoStmt env _ (BodyStmtA rhs then_op _) res_ty thing_inside = do { (rhs', elt_ty) <- tc_arr_rhs env rhs ; thing <- thing_inside res_ty ; s <- newFlexiTyVarTy liftedTypeKind ; b <- newFlexiTyVarTy liftedTypeKind ; c <- newFlexiTyVarTy liftedTypeKind ; then_op' <- tcSyntaxOp DoOrigin then_op (mkFunTys [ mkCmdArrTy env (mkBoxedTupleTy [elt_ty, s]) b , mkCmdArrTy env (mkBoxedTupleTy [elt_ty, s]) c] (mkCmdArrTy env (mkBoxedTupleTy [elt_ty, s]) c)) ; return (BodyStmtA rhs' then_op' elt_ty, thing) } }}} The test function I'm compiling looks like this: {{{ test :: Arrow a => a i i test = proc n -> do (arr id) -< n returnA -< n }}} Using `-dcore-lint` during complation reveals offences similar to the ones I experienced earlier: {{{ Argument value doesn't match argument type: Fun type: a_auK (i_auL, GHC.Prim.Any) GHC.Prim.Any -> a_auK (i_auL, GHC.Prim.Any) GHC.Prim.Any -> a_auK (i_auL, GHC.Prim.Any) GHC.Prim.Any Arg type: a_auK (i_auL, ()) i_auL Arg: ds_dvR @ (i_auL, ()) @ i_auL @ i_auL (ds_dvQ @ (i_auL, ()) @ i_auL (\ (ds_dw0 :: (i_auL, ())) -> case ds_dw0 of _ [Occ=Dead] { (ds_dvZ, _ [Occ=Dead]) -> ds_dvZ })) (Control.Arrow.arr @ a_auK $dArrow_auX @ i_auL @ i_auL (T7828.id @ i_auL)) }}} I tried to write the typechecking of `thenA` to match the actual type, just like you wrote in [ticket:7828#comment:29]. But I don't see how could I replace my new type variables `s`, `b` and `c` with something concrete. I believe that `s` should be allowed to be anything (polymorphism in the environment), so I don't know what could it be other than a new tyvar. Tracing the calls lead me to believe that `res_ty` is the type of the whole `do` expression, so I don't think it has anything to do with the type of `thenA`. Can I ask for your guidance here? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7828#comment:41 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler