Big tidy-up of deriving code

[ghc-hetmet.git] / compiler / typecheck / TcInstDcls.lhs

diff --git a/compiler/typecheck/TcInstDcls.lhs b/compiler/typecheck/TcInstDcls.lhs
index 8b53e3e..fe7b1d8 100644 (file)
--- a/compiler/typecheck/TcInstDcls.lhs
+++ b/compiler/typecheck/TcInstDcls.lhs
@@ -1,7 +1,9 @@
 %
 %

+% (c) The University of Glasgow 2006

 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
 %
 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
 %

-\section[TcInstDecls]{Typechecking instance declarations}
+
+TcInstDecls: Typechecking instance declarations

 
 \begin{code}
 module TcInstDcls ( tcInstDecls1, tcInstDecls2 ) where
 
 \begin{code}
 module TcInstDcls ( tcInstDecls1, tcInstDecls2 ) where

@@ -9,36 +11,43 @@ module TcInstDcls ( tcInstDecls1, tcInstDecls2 ) where
 #include "HsVersions.h"
 
 import HsSyn
 #include "HsVersions.h"
 
 import HsSyn

-import TcBinds         ( mkPragFun, tcPrags, badBootDeclErr )
-import TcClassDcl      ( tcMethodBind, mkMethodBind, badMethodErr, 
-                         tcClassDecl2, getGenericInstances )
+import TcBinds
+import TcTyClsDecls
+import TcClassDcl

 import TcRnMonad       
 import TcRnMonad       

-import TcMType         ( tcSkolSigType, checkValidInstance, checkValidInstHead )
-import TcType          ( mkClassPred, tcSplitSigmaTy, tcSplitDFunHead, mkTyVarTys,
-                         SkolemInfo(InstSkol), tcSplitDFunTy )
-import Inst            ( tcInstClassOp, newDicts, instToId, showLIE, 
-                         getOverlapFlag, tcExtendLocalInstEnv )
-import InstEnv         ( mkLocalInstance, instanceDFunId )
-import TcDeriv         ( tcDeriving )
-import TcEnv           ( InstInfo(..), InstBindings(..), 
-                         newDFunName, tcExtendIdEnv
-                       )
-import TcHsType                ( kcHsSigType, tcHsKindedType )
-import TcUnify         ( checkSigTyVars )
-import TcSimplify      ( tcSimplifyCheck, tcSimplifySuperClasses )
-import Type            ( zipOpenTvSubst, substTheta, substTys )
-import DataCon         ( classDataCon )
-import Class           ( classBigSig )
-import Var             ( Id, idName, idType )
-import MkId            ( mkDictFunId )
-import Name            ( Name, getSrcLoc )
-import Maybe           ( catMaybes )
-import SrcLoc          ( srcLocSpan, unLoc, noLoc, Located(..), srcSpanStart )
-import ListSetOps      ( minusList )
+import TcMType
+import TcType
+import Inst
+import InstEnv
+import FamInst
+import FamInstEnv
+import TcDeriv
+import TcEnv
+import TcHsType
+import TcUnify
+import TcSimplify
+import Type
+import Coercion
+import TyCon
+import DataCon
+import Class
+import Var
+import MkId
+import Name
+import NameSet
+import DynFlags
+import SrcLoc
+import ListSetOps
+import Util

 import Outputable
 import Bag
 import Outputable
 import Bag

-import BasicTypes      ( Activation( AlwaysActive ), InlineSpec(..) )
+import BasicTypes
+import HscTypes

 import FastString
 import FastString

+
+import Data.Maybe
+import Control.Monad hiding (zipWithM_, mapAndUnzipM)
+import Data.List

 \end{code}
 
 Typechecking instance declarations is done in two passes. The first
 \end{code}
 
 Typechecking instance declarations is done in two passes. The first

@@ -51,7 +60,6 @@ pass, when the class-instance envs and GVE contain all the info from
 all the instance and value decls.  Indeed that's the reason we need
 two passes over the instance decls.
 
 all the instance and value decls.  Indeed that's the reason we need
 two passes over the instance decls.
 

-

 Here is the overall algorithm.
 Assume that we have an instance declaration
 
 Here is the overall algorithm.
 Assume that we have an instance declaration
 

@@ -127,58 +135,104 @@ Gather up the instance declarations from their various sources
 tcInstDecls1   -- Deal with both source-code and imported instance decls
    :: [LTyClDecl Name]         -- For deriving stuff
    -> [LInstDecl Name]         -- Source code instance decls
 tcInstDecls1   -- Deal with both source-code and imported instance decls
    :: [LTyClDecl Name]         -- For deriving stuff
    -> [LInstDecl Name]         -- Source code instance decls

+   -> [LDerivDecl Name]                -- Source code stand-alone deriving decls

    -> TcM (TcGblEnv,           -- The full inst env
           [InstInfo],          -- Source-code instance decls to process; 
                                -- contains all dfuns for this module
           HsValBinds Name)     -- Supporting bindings for derived instances
 
    -> TcM (TcGblEnv,           -- The full inst env
           [InstInfo],          -- Source-code instance decls to process; 
                                -- contains all dfuns for this module
           HsValBinds Name)     -- Supporting bindings for derived instances
 

-tcInstDecls1 tycl_decls inst_decls
+tcInstDecls1 tycl_decls inst_decls deriv_decls

   = checkNoErrs $
   = checkNoErrs $

-       -- Stop if addInstInfos etc discovers any errors
-       -- (they recover, so that we get more than one error each round)
-
-       -- (1) Do the ordinary instance declarations
-    mappM tcLocalInstDecl1 inst_decls    `thenM` \ local_inst_infos ->
-
-    let
-       local_inst_info = catMaybes local_inst_infos
-       clas_decls      = filter (isClassDecl.unLoc) tycl_decls
-    in
-       -- (2) Instances from generic class declarations
-    getGenericInstances clas_decls     `thenM` \ generic_inst_info -> 
-
-       -- Next, construct the instance environment so far, consisting of
-       --      a) local instance decls
-       --      b) generic instances
-    addInsts local_inst_info   $
-    addInsts generic_inst_info $
-
-       -- (3) Compute instances from "deriving" clauses; 
-       -- This stuff computes a context for the derived instance decl, so it
-       -- needs to know about all the instances possible; hence inst_env4
-    tcDeriving tycl_decls      `thenM` \ (deriv_inst_info, deriv_binds) ->
-    addInsts deriv_inst_info   $
-
-    getGblEnv                  `thenM` \ gbl_env ->
-    returnM (gbl_env, 
-            generic_inst_info ++ deriv_inst_info ++ local_inst_info,
-            deriv_binds)
+    do {        -- Stop if addInstInfos etc discovers any errors
+               -- (they recover, so that we get more than one error each
+               -- round) 
+
+               -- (1) Do class instance declarations and instances of indexed
+               --     types 
+       ; let { idxty_decls = filter (isIdxTyDecl . unLoc) tycl_decls }
+       ; local_info_tycons <- mappM tcLocalInstDecl1  inst_decls
+       ; idx_tycons        <- mappM tcIdxTyInstDeclTL idxty_decls
+
+       ; let { (local_infos,
+               at_tycons)     = unzip local_info_tycons
+            ; local_info      = concat local_infos
+            ; at_idx_tycon    = concat at_tycons ++ catMaybes idx_tycons
+            ; clas_decls      = filter (isClassDecl.unLoc) tycl_decls 
+            ; implicit_things = concatMap implicitTyThings at_idx_tycon
+            }
+
+               -- (2) Add the tycons of indexed types and their implicit
+               --     tythings to the global environment
+       ; tcExtendGlobalEnv (at_idx_tycon ++ implicit_things) $ do {
+
+               -- (3) Instances from generic class declarations
+       ; generic_inst_info <- getGenericInstances clas_decls
+
+               -- Next, construct the instance environment so far, consisting
+               -- of 
+               --   a) local instance decls
+               --   b) generic instances
+               --   c) local family instance decls
+       ; addInsts local_info         $ do {
+       ; addInsts generic_inst_info  $ do {
+       ; addFamInsts at_idx_tycon    $ do {
+
+               -- (4) Compute instances from "deriving" clauses; 
+               -- This stuff computes a context for the derived instance
+               -- decl, so it needs to know about all the instances possible
+       ; (deriv_inst_info, deriv_binds) <- tcDeriving tycl_decls deriv_decls
+       ; addInsts deriv_inst_info   $ do {
+
+       ; gbl_env <- getGblEnv
+       ; returnM (gbl_env, 
+                 generic_inst_info ++ deriv_inst_info ++ local_info,
+                 deriv_binds) 
+    }}}}}}
+  where
+    -- Make sure that toplevel type instance are not for associated types.
+    -- !!!TODO: Need to perform this check for the TyThing of type functions,
+    --         too.
+    tcIdxTyInstDeclTL ldecl@(L loc decl) =
+      do { tything <- tcIdxTyInstDecl ldecl
+        ; setSrcSpan loc $
+            when (isAssocFamily tything) $
+              addErr $ assocInClassErr (tcdName decl)
+        ; return tything
+        }
+    isAssocFamily (Just (ATyCon tycon)) =
+      case tyConFamInst_maybe tycon of
+        Nothing       -> panic "isAssocFamily: no family?!?"
+       Just (fam, _) -> isTyConAssoc fam
+    isAssocFamily (Just _            ) = panic "isAssocFamily: no tycon?!?"
+    isAssocFamily Nothing               = False
+
+assocInClassErr name = 
+  ptext SLIT("Associated type") <+> quotes (ppr name) <+> 
+  ptext SLIT("must be inside a class instance")

 
 addInsts :: [InstInfo] -> TcM a -> TcM a
 addInsts infos thing_inside
   = tcExtendLocalInstEnv (map iSpec infos) thing_inside
 
 addInsts :: [InstInfo] -> TcM a -> TcM a
 addInsts infos thing_inside
   = tcExtendLocalInstEnv (map iSpec infos) thing_inside

-\end{code} 
+
+addFamInsts :: [TyThing] -> TcM a -> TcM a
+addFamInsts tycons thing_inside
+  = tcExtendLocalFamInstEnv (map mkLocalFamInstTyThing tycons) thing_inside
+  where
+    mkLocalFamInstTyThing (ATyCon tycon) = mkLocalFamInst tycon
+    mkLocalFamInstTyThing tything       = pprPanic "TcInstDcls.addFamInsts"
+                                                   (ppr tything)
+\end{code}

 
 \begin{code}
 tcLocalInstDecl1 :: LInstDecl Name 
 
 \begin{code}
 tcLocalInstDecl1 :: LInstDecl Name 

-                -> TcM (Maybe InstInfo)        -- Nothing if there was an error
+                -> TcM ([InstInfo], [TyThing]) -- [] if there was an error

        -- A source-file instance declaration
        -- Type-check all the stuff before the "where"
        --
        -- We check for respectable instance type, and context
        -- A source-file instance declaration
        -- Type-check all the stuff before the "where"
        --
        -- We check for respectable instance type, and context

-tcLocalInstDecl1 decl@(L loc (InstDecl poly_ty binds uprags))
+tcLocalInstDecl1 decl@(L loc (InstDecl poly_ty binds uprags ats))

   =    -- Prime error recovery, set source location
   =    -- Prime error recovery, set source location

-    recoverM (returnM Nothing)         $
+    recoverM (returnM ([], []))                $

     setSrcSpan loc                     $
     addErrCtxt (instDeclCtxt1 poly_ty) $
 
     setSrcSpan loc                     $
     addErrCtxt (instDeclCtxt1 poly_ty) $
 

@@ -186,21 +240,120 @@ tcLocalInstDecl1 decl@(L loc (InstDecl poly_ty binds uprags))
        ; checkTc (not is_boot || (isEmptyLHsBinds binds && null uprags))
                  badBootDeclErr
 
        ; checkTc (not is_boot || (isEmptyLHsBinds binds && null uprags))
                  badBootDeclErr
 

-       -- Typecheck the instance type itself.  We can't use 
-       -- tcHsSigType, because it's not a valid user type.
-       ; kinded_ty <- kcHsSigType poly_ty
-       ; poly_ty'  <- tcHsKindedType kinded_ty
-       ; let (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
+       ; (tyvars, theta, tau) <- tcHsInstHead poly_ty

        
        

+       -- Next, process any associated types.
+       ; idx_tycons <- mappM tcIdxTyInstDecl ats
+
+       -- Now, check the validity of the instance.

        ; (clas, inst_tys) <- checkValidInstHead tau
        ; checkValidInstance tyvars theta clas inst_tys
        ; (clas, inst_tys) <- checkValidInstHead tau
        ; checkValidInstance tyvars theta clas inst_tys

+       ; checkValidAndMissingATs clas (tyvars, inst_tys) 
+                                 (zip ats idx_tycons)

 
 

+       -- Finally, construct the Core representation of the instance.
+       -- (This no longer includes the associated types.)

        ; dfun_name <- newDFunName clas inst_tys (srcSpanStart loc)
        ; overlap_flag <- getOverlapFlag
        ; dfun_name <- newDFunName clas inst_tys (srcSpanStart loc)
        ; overlap_flag <- getOverlapFlag

-       ; let dfun  = mkDictFunId dfun_name tyvars theta clas inst_tys
-             ispec = mkLocalInstance dfun overlap_flag
+       ; let dfun           = mkDictFunId dfun_name tyvars theta clas inst_tys
+             ispec          = mkLocalInstance dfun overlap_flag

 
 

-       ; return (Just (InstInfo { iSpec = ispec, iBinds = VanillaInst binds uprags })) }
+       ; return ([InstInfo { iSpec  = ispec, 
+                             iBinds = VanillaInst binds uprags }],
+                 catMaybes idx_tycons)
+        }
+  where
+    -- We pass in the source form and the type checked form of the ATs.  We
+    -- really need the source form only to be able to produce more informative
+    -- error messages.
+    checkValidAndMissingATs :: Class
+                           -> ([TyVar], [TcType])     -- instance types
+                           -> [(LTyClDecl Name,       -- source form of AT
+                                Maybe TyThing)]       -- Core form of AT
+                           -> TcM ()
+    checkValidAndMissingATs clas inst_tys ats
+      = do { -- Issue a warning for each class AT that is not defined in this
+            -- instance.
+          ; let classDefATs = listToNameSet . map tyConName . classATs $ clas
+                 definedATs  = listToNameSet . map (tcdName.unLoc.fst)  $ ats
+                omitted     = classDefATs `minusNameSet` definedATs
+          ; warn <- doptM Opt_WarnMissingMethods
+          ; mapM_ (warnTc warn . omittedATWarn) (nameSetToList omitted)
+          
+            -- Ensure that all AT indexes that correspond to class parameters
+            -- coincide with the types in the instance head.  All remaining
+            -- AT arguments must be variables.  Also raise an error for any
+            -- type instances that are not associated with this class.
+          ; mapM_ (checkIndexes clas inst_tys) ats
+          }
+
+    checkIndexes _    _        (hsAT, Nothing)             = 
+      return ()           -- skip, we already had an error here
+    checkIndexes clas inst_tys (hsAT, Just (ATyCon tycon)) = 
+-- !!!TODO: check that this does the Right Thing for indexed synonyms, too!
+      checkIndexes' clas inst_tys hsAT 
+                   (tyConTyVars tycon, 
+                    snd . fromJust . tyConFamInst_maybe $ tycon)
+    checkIndexes _ _ _ = panic "checkIndexes"
+
+    checkIndexes' clas (instTvs, instTys) hsAT (atTvs, atTys)
+      = let atName = tcdName . unLoc $ hsAT
+       in
+       setSrcSpan (getLoc hsAT)       $
+       addErrCtxt (atInstCtxt atName) $
+       case find ((atName ==) . tyConName) (classATs clas) of
+         Nothing     -> addErrTc $ badATErr clas atName  -- not in this class
+         Just atDecl -> 
+           case assocTyConArgPoss_maybe atDecl of
+             Nothing   -> panic "checkIndexes': AT has no args poss?!?"
+             Just poss -> 
+
+               -- The following is tricky!  We need to deal with three
+               -- complications: (1) The AT possibly only uses a subset of
+               -- the class parameters as indexes and those it uses may be in
+               -- a different order; (2) the AT may have extra arguments,
+               -- which must be type variables; and (3) variables in AT and
+               -- instance head will be different `Name's even if their
+               -- source lexemes are identical.
+               --
+               -- Re (1), `poss' contains a permutation vector to extract the
+               -- class parameters in the right order.
+               --
+               -- Re (2), we wrap the (permuted) class parameters in a Maybe
+               -- type and use Nothing for any extra AT arguments.  (First
+               -- equation of `checkIndex' below.)
+               --
+               -- Re (3), we replace any type variable in the AT parameters
+               -- that has the same source lexeme as some variable in the
+               -- instance types with the instance type variable sharing its
+               -- source lexeme.
+               --
+               let relevantInstTys = map (instTys !!) poss
+                   instArgs        = map Just relevantInstTys ++ 
+                                     repeat Nothing  -- extra arguments
+                   renaming        = substSameTyVar atTvs instTvs
+               in
+               zipWithM_ checkIndex (substTys renaming atTys) instArgs
+
+    checkIndex ty Nothing 
+      | isTyVarTy ty         = return ()
+      | otherwise            = addErrTc $ mustBeVarArgErr ty
+    checkIndex ty (Just instTy) 
+      | ty `tcEqType` instTy = return ()
+      | otherwise            = addErrTc $ wrongATArgErr ty instTy
+
+    listToNameSet = addListToNameSet emptyNameSet 
+
+    substSameTyVar []       _            = emptyTvSubst
+    substSameTyVar (tv:tvs) replacingTvs = 
+      let replacement = case find (tv `sameLexeme`) replacingTvs of
+                         Nothing  -> mkTyVarTy tv
+                         Just rtv -> mkTyVarTy rtv
+          --
+          tv1 `sameLexeme` tv2 = 
+           nameOccName (tyVarName tv1) == nameOccName (tyVarName tv2)
+      in
+      extendTvSubst (substSameTyVar tvs replacingTvs) tv replacement

 \end{code}
 
 
 \end{code}
 
 

@@ -303,11 +456,132 @@ First comes the easy case of a non-local instance decl.
 
 \begin{code}
 tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)
 
 \begin{code}
 tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)

+-- Returns a binding for the dfun
+
+------------------------
+-- Derived newtype instances; surprisingly tricky!
+--
+-- In the case of a newtype, things are rather easy
+--     class Show a => Foo a b where ...
+--     newtype T a = MkT (Tree [a]) deriving( Foo Int )
+-- The newtype gives an FC axiom looking like
+--     axiom CoT a ::  T a :=: Tree [a]
+--   (see Note [Newtype coercions] in TyCon for this unusual form of axiom)
+--
+-- So all need is to generate a binding looking like: 
+--     dfunFooT :: forall a. (Foo Int (Tree [a], Show (T a)) => Foo Int (T a)
+--     dfunFooT = /\a. \(ds:Show (T a)) (df:Foo (Tree [a])).
+--               case df `cast` (Foo Int (sym (CoT a))) of
+--                  Foo _ op1 .. opn -> Foo ds op1 .. opn
+--
+-- If there are no superclasses, matters are simpler, because we don't need the case
+-- see Note [Newtype deriving superclasses] in TcDeriv.lhs
+
+tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = NewTypeDerived mb_preds })
+  = do { let dfun_id      = instanceDFunId ispec 
+             rigid_info   = InstSkol
+             origin       = SigOrigin rigid_info
+             inst_ty      = idType dfun_id
+       ; (tvs, theta, inst_head_ty) <- tcSkolSigType rigid_info inst_ty
+               -- inst_head_ty is a PredType
+
+       ; inst_loc <- getInstLoc origin
+       ; (rep_dict_id : sc_dict_ids, wrap_fn, sc_binds)
+               <- make_wrapper inst_loc tvs theta mb_preds
+               -- Here, we are relying on the order of dictionary 
+               -- arguments built by NewTypeDerived in TcDeriv; 
+               -- namely, that the rep_dict_id comes first
+          
+        ; let (cls, cls_inst_tys) = tcSplitDFunHead inst_head_ty
+             cls_tycon           = classTyCon cls
+             the_coercion        = make_coercion cls_tycon cls_inst_tys
+              coerced_rep_dict           = mkHsWrap the_coercion (HsVar rep_dict_id)
+
+       ; body <- make_body cls_tycon cls_inst_tys sc_dict_ids coerced_rep_dict
+              
+        ; return (sc_binds `snocBag` (noLoc $ VarBind dfun_id $ noLoc $ mkHsWrap wrap_fn body)) }
+  where

 
 

-tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = binds })
+      -----------------------
+      --       make_wrapper
+      -- We distinguish two cases:
+      -- (a) there is no tyvar abstraction in the dfun, so all dicts are constant,
+      --     and the new dict can just be a constant
+      --       (mb_preds = Just preds)
+      -- (b) there are tyvars, so we must make a dict *fun*
+      --       (mb_preds = Nothing)
+      -- See the defn of NewTypeDerived for the meaning of mb_preds
+    make_wrapper inst_loc tvs theta (Just preds)       -- Case (a)
+      = ASSERT( null tvs && null theta )
+       do { dicts <- newDictBndrs inst_loc preds
+          ; sc_binds <- addErrCtxt superClassCtxt $
+                        tcSimplifySuperClasses inst_loc [] dicts
+               -- Use tcSimplifySuperClasses to avoid creating loops, for the
+               -- same reason as Note [SUPERCLASS-LOOP 1] in TcSimplify
+          ; return (map instToId dicts, idHsWrapper, sc_binds) }
+
+    make_wrapper inst_loc tvs theta Nothing    -- Case (b)
+      = do { dicts <- newDictBndrs inst_loc theta
+          ; let dict_ids = map instToId dicts
+          ; return (dict_ids, mkWpTyLams tvs <.> mkWpLams dict_ids, emptyBag) }
+
+      -----------------------
+      --       make_coercion
+      -- The inst_head looks like (C s1 .. sm (T a1 .. ak))
+      -- But we want the coercion (C s1 .. sm (sym (CoT a1 .. ak)))
+      --       with kind (C s1 .. sm (T a1 .. ak)  :=:  C s1 .. sm <rep_ty>)
+      --       where rep_ty is the (eta-reduced) type rep of T
+      -- So we just replace T with CoT, and insert a 'sym'
+      -- NB: we know that k will be >= arity of CoT, because the latter fully eta-reduced
+
+    make_coercion cls_tycon cls_inst_tys
+       | Just (all_tys_but_last, last_ty) <- snocView cls_inst_tys
+       , (tycon, tc_args) <- tcSplitTyConApp last_ty   -- Should not fail
+       , Just co_con <- newTyConCo_maybe tycon
+       , let co = mkSymCoercion (mkTyConApp co_con tc_args)
+        = WpCo (mkTyConApp cls_tycon (all_tys_but_last ++ [co]))
+        | otherwise    -- The newtype is transparent; no need for a cast
+        = idHsWrapper
+
+      -----------------------
+      --       make_body
+      -- Two cases; see Note [Newtype deriving superclasses] in TcDeriv.lhs
+      -- (a) no superclasses; then we can just use the coerced dict
+      -- (b) one or more superclasses; then new need to do the unpack/repack
+       
+    make_body cls_tycon cls_inst_tys sc_dict_ids coerced_rep_dict
+       | null sc_dict_ids              -- Case (a)
+       = return coerced_rep_dict
+       | otherwise                     -- Case (b)
+       = do { op_ids            <- newSysLocalIds FSLIT("op") op_tys
+            ; dummy_sc_dict_ids <- newSysLocalIds FSLIT("sc") (map idType sc_dict_ids)
+            ; let the_pat = ConPatOut { pat_con = noLoc cls_data_con, pat_tvs = [],
+                                        pat_dicts = dummy_sc_dict_ids,
+                                        pat_binds = emptyLHsBinds,
+                                        pat_args = PrefixCon (map nlVarPat op_ids),
+                                        pat_ty = pat_ty} 
+                  the_match = mkSimpleMatch [noLoc the_pat] the_rhs
+                  the_rhs = mkHsConApp cls_data_con cls_inst_tys $
+                            map HsVar (sc_dict_ids ++ op_ids)
+
+               -- Warning: this HsCase scrutinises a value with a PredTy, which is
+               --          never otherwise seen in Haskell source code. It'd be
+               --          nicer to generate Core directly!
+            ; return (HsCase (noLoc coerced_rep_dict) $
+                      MatchGroup [the_match] (mkFunTy pat_ty pat_ty)) }
+       where
+         pat_ty       = mkTyConApp cls_tycon cls_inst_tys
+          cls_data_con = head (tyConDataCons cls_tycon)
+          cls_arg_tys  = dataConInstArgTys cls_data_con cls_inst_tys 
+          op_tys       = dropList sc_dict_ids cls_arg_tys
+
+------------------------
+-- Ordinary instances
+
+tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = VanillaInst monobinds uprags })

   = let 
        dfun_id    = instanceDFunId ispec
   = let 
        dfun_id    = instanceDFunId ispec

-       rigid_info = InstSkol dfun_id
+       rigid_info = InstSkol

        inst_ty    = idType dfun_id
     in
         -- Prime error recovery
        inst_ty    = idType dfun_id
     in
         -- Prime error recovery

@@ -329,9 +603,11 @@ tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = binds })
        origin    = SigOrigin rigid_info
     in
         -- Create dictionary Ids from the specified instance contexts.
        origin    = SigOrigin rigid_info
     in
         -- Create dictionary Ids from the specified instance contexts.

-    newDicts InstScOrigin sc_theta'                    `thenM` \ sc_dicts ->
-    newDicts origin dfun_theta'                                `thenM` \ dfun_arg_dicts ->
-    newDicts origin [mkClassPred clas inst_tys']       `thenM` \ [this_dict] ->
+    getInstLoc InstScOrigin                            `thenM` \ sc_loc -> 
+    newDictBndrs sc_loc sc_theta'                      `thenM` \ sc_dicts ->
+    getInstLoc origin                                  `thenM` \ inst_loc -> 
+    newDictBndrs inst_loc dfun_theta'                  `thenM` \ dfun_arg_dicts ->
+    newDictBndr inst_loc (mkClassPred clas inst_tys')   `thenM` \ this_dict ->

                -- Default-method Ids may be mentioned in synthesised RHSs,
                -- but they'll already be in the environment.
 
                -- Default-method Ids may be mentioned in synthesised RHSs,
                -- but they'll already be in the environment.
 

@@ -341,27 +617,21 @@ tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = binds })
     in
     tcMethods origin clas inst_tyvars' 
              dfun_theta' inst_tys' avail_insts 
     in
     tcMethods origin clas inst_tyvars' 
              dfun_theta' inst_tys' avail_insts 

-             op_items binds            `thenM` \ (meth_ids, meth_binds) ->
+             op_items monobinds uprags         `thenM` \ (meth_ids, meth_binds) ->

 
        -- Figure out bindings for the superclass context
        -- Don't include this_dict in the 'givens', else
        -- sc_dicts get bound by just selecting  from this_dict!!
     addErrCtxt superClassCtxt
 
        -- Figure out bindings for the superclass context
        -- Don't include this_dict in the 'givens', else
        -- sc_dicts get bound by just selecting  from this_dict!!
     addErrCtxt superClassCtxt

-       (tcSimplifySuperClasses inst_tyvars'
-                        dfun_arg_dicts
-                        sc_dicts)      `thenM` \ sc_binds ->
+       (tcSimplifySuperClasses inst_loc
+                        dfun_arg_dicts sc_dicts)       `thenM` \ sc_binds ->

 
        -- It's possible that the superclass stuff might unified one
        -- of the inst_tyavars' with something in the envt
     checkSigTyVars inst_tyvars'        `thenM_`
 
        -- Deal with 'SPECIALISE instance' pragmas 
 
        -- It's possible that the superclass stuff might unified one
        -- of the inst_tyavars' with something in the envt
     checkSigTyVars inst_tyvars'        `thenM_`
 
        -- Deal with 'SPECIALISE instance' pragmas 

-    let
-       specs = case binds of
-                 VanillaInst _ prags -> filter isSpecInstLSig prags
-                 other               -> []
-    in
-    tcPrags dfun_id specs                      `thenM` \ prags -> 
+    tcPrags dfun_id (filter isSpecInstLSig uprags)     `thenM` \ prags -> 

     
        -- Create the result bindings
     let
     
        -- Create the result bindings
     let

@@ -405,7 +675,7 @@ tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = binds })
 
 
 tcMethods origin clas inst_tyvars' dfun_theta' inst_tys' 
 
 
 tcMethods origin clas inst_tyvars' dfun_theta' inst_tys' 

-         avail_insts op_items (VanillaInst monobinds uprags)
+         avail_insts op_items monobinds uprags

   =    -- Check that all the method bindings come from this class
     let
        sel_names = [idName sel_id | (sel_id, _) <- op_items]
   =    -- Check that all the method bindings come from this class
     let
        sel_names = [idName sel_id | (sel_id, _) <- op_items]

@@ -461,41 +731,6 @@ tcMethods origin clas inst_tyvars' dfun_theta' inst_tys'
     mapM tc_method_bind meth_infos             `thenM` \ meth_binds_s ->
    
     returnM (meth_ids, unionManyBags meth_binds_s)
     mapM tc_method_bind meth_infos             `thenM` \ meth_binds_s ->
    
     returnM (meth_ids, unionManyBags meth_binds_s)

-
-
--- Derived newtype instances
-tcMethods origin clas inst_tyvars' dfun_theta' inst_tys' 
-         avail_insts op_items (NewTypeDerived rep_tys)
-  = getInstLoc origin                          `thenM` \ inst_loc ->
-    mapAndUnzip3M (do_one inst_loc) op_items   `thenM` \ (meth_ids, meth_binds, rhs_insts) ->
-    
-    tcSimplifyCheck
-        (ptext SLIT("newtype derived instance"))
-        inst_tyvars' avail_insts rhs_insts     `thenM` \ lie_binds ->
-
-       -- I don't think we have to do the checkSigTyVars thing
-
-    returnM (meth_ids, lie_binds `unionBags` listToBag meth_binds)
-
-  where
-    do_one inst_loc (sel_id, _)
-       = -- The binding is like "op @ NewTy = op @ RepTy"
-               -- Make the *binder*, like in mkMethodBind
-         tcInstClassOp inst_loc sel_id inst_tys'       `thenM` \ meth_inst ->
-
-               -- Make the *occurrence on the rhs*
-         tcInstClassOp inst_loc sel_id rep_tys'        `thenM` \ rhs_inst ->
-         let
-            meth_id = instToId meth_inst
-         in
-         return (meth_id, noLoc (VarBind meth_id (nlHsVar (instToId rhs_inst))), rhs_inst)
-
-       -- Instantiate rep_tys with the relevant type variables
-       -- This looks a bit odd, because inst_tyvars' are the skolemised version
-       -- of the type variables in the instance declaration; but rep_tys doesn't
-       -- have the skolemised version, so we substitute them in here
-    rep_tys' = substTys subst rep_tys
-    subst    = zipOpenTvSubst inst_tyvars' (mkTyVarTys inst_tyvars')

 \end{code}
 
 
 \end{code}
 
 

@@ -610,4 +845,19 @@ instDeclCtxt2 dfun_ty
 inst_decl_ctxt doc = ptext SLIT("In the instance declaration for") <+> quotes doc
 
 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")
 inst_decl_ctxt doc = ptext SLIT("In the instance declaration for") <+> quotes doc
 
 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")

+
+atInstCtxt name = ptext SLIT("In the associated type instance for") <+> 
+                 quotes (ppr name)
+
+mustBeVarArgErr ty = 
+  sep [ ptext SLIT("Arguments that do not correspond to a class parameter") <+>
+        ptext SLIT("must be variables")
+      , ptext SLIT("Instead of a variable, found") <+> ppr ty
+      ]
+
+wrongATArgErr ty instTy =
+  sep [ ptext SLIT("Type indexes must match class instance head")
+      , ptext SLIT("Found") <+> ppr ty <+> ptext SLIT("but expected") <+>
+         ppr instTy
+      ]

 \end{code}
 \end{code}