[GHC] #7828: RebindableSyntax and Arrow

[GHC]

#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:
----------------------------------------------+----------------------------

Comment (by jstolarek):

 In my work on the prototype I've ran into a problem I can't solve. Since
 desugaring of `HsCmdTop`
 [https://github.com/ghc/ghc/blob/165ac4af4a1002eff5f5a474bc21bc443c8f8c63/compiler/deSugar/DsArrows.lhs#L292
 requires calls to arr and >>>] I've added two `SyntaxExpr` to `HsCmdTop`
 datatype. These two `SyntaxExpr`s
 [https://github.com/ghc/ghc/blob/165ac4af4a1002eff5f5a474bc21bc443c8f8c63/compiler/typecheck/TcArrows.lhs#L128
 need to be typechecked in tcCmdTop]. I've see earlier how
 [https://github.com/ghc/ghc/blob/165ac4af4a1002eff5f5a474bc21bc443c8f8c63/compiler/typecheck/TcMatches.lhs#L761
 typechecking of the do-notation bind is implemented] and decided to adopt
 a similar aproach:

 {{{
 tcCmdTop env (L loc (HsCmdTop cmd _ _ names compose_op arr_op))
 cmd_ty@(cmd_stk, res_ty)
   = setSrcSpan loc $
     do  { cmd'   <- tcCmd env cmd cmd_ty
         ; names' <- mapM (tcSyntaxName ProcOrigin (cmd_arr env)) names
         -- VOODOO CODING based on typechecking of >>= in TcMatches
         -- is it correct to use b and c variables for typechecking in both
         -- arr and compose?
         ; a       <- newFlexiTyVarTy liftedTypeKind
         ; b       <- newFlexiTyVarTy liftedTypeKind
         ; c       <- newFlexiTyVarTy liftedTypeKind
         ; arr_op' <- tcSyntaxOp DoOrigin arr_op
                                 (mkFunTy (mkFunTy b c) (mkCmdArrTy env b
 c))

         ; compose_op' <- tcSyntaxOp DoOrigin compose_op
                                 (mkFunTys [mkCmdArrTy env a b, mkCmdArrTy
 env b c] (mkCmdArrTy env a c))
         ; return (L loc $ HsCmdTop cmd' cmd_stk res_ty names' compose_op'
 arr_op') }
 }}}

 This however ends with a panic. Using `-dcore-lint` gives me this:

 {{{
 *** Core Lint errors : in result of Desugar (after optimization) ***
 <no location info>: Warning:
 In the expression: T7828.>>>
                      @ GHC.Prim.Any
                      @ GHC.Prim.Any
                      @ GHC.Prim.Any
                      @ a_aEo
                      @ (a_aEo, ())
                      @ a_aEo
                      (T7828.arr
                         @ GHC.Prim.Any
                         @ GHC.Prim.Any
                         @ a_aEo
                         @ (a_aEo, ())
                         (\ (n_aus :: a_aEo) -> (n_aus, GHC.Tuple.())))
                      (T7828.>>>
                         @ (a_aEo, ())
                         @ a_aEo
                         @ a_aEo
                         (T7828.arr
                            @ (a_aEo, ())
                            @ a_aEo
                            (\ (ds_dGU :: (a_aEo, ())) ->
                               case ds_dGU of _ [Occ=Dead] { (ds_dGT, _
 [Occ=Dead]) -> ds_dGT }))
                         (T7828.returnA @ a_aEo))
 Illegal type application:
 Exp type:
     T7828.R GHC.Prim.Any GHC.Prim.Any
     -> T7828.R GHC.Prim.Any GHC.Prim.Any
     -> T7828.R GHC.Prim.Any GHC.Prim.Any :: *
 Arg type: a_aEo :: *
 }}}
 These `GHC.Prim.Any` look wrong. Notice that there are two calls of `>>>`
 and `arr` but only one of each has these extra `GHC.Prim.Any` parameters.
 The incorrect `>>>` and `arr` are generated by my modified `HsCmdTop`. The
 other pair of `>>>` and `arr` is generated by `HsCmdArrApp` constructor,
 which has not been modified yet. Simon, help?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7828#comment:24>
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