Several fixes to 'deriving' including Trac #2378

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

diff --git a/compiler/typecheck/TcInstDcls.lhs b/compiler/typecheck/TcInstDcls.lhs
index 21c8928..1f800d9 100644 (file)
--- a/compiler/typecheck/TcInstDcls.lhs
+++ b/compiler/typecheck/TcInstDcls.lhs
@@ -8,13 +8,11 @@ TcInstDecls: Typechecking instance declarations
 \begin{code}
 module TcInstDcls ( tcInstDecls1, tcInstDecls2 ) where
 
 \begin{code}
 module TcInstDcls ( tcInstDecls1, tcInstDecls2 ) where
 

-#include "HsVersions.h"
-

 import HsSyn
 import TcBinds
 import TcTyClsDecls
 import TcClassDcl
 import HsSyn
 import TcBinds
 import TcTyClsDecls
 import TcClassDcl

-import TcRnMonad       
+import TcRnMonad

 import TcMType
 import TcType
 import Inst
 import TcMType
 import TcType
 import Inst

@@ -47,7 +45,7 @@ import HscTypes
 import FastString
 
 import Data.Maybe
 import FastString
 
 import Data.Maybe

-import Control.Monad hiding (zipWithM_, mapAndUnzipM)
+import Control.Monad

 import Data.List
 \end{code}
 
 import Data.List
 \end{code}
 

@@ -112,12 +110,12 @@ Create final dictionary function from bindings generated already
 \begin{pseudocode}
 df = lambda inst_tyvars
        lambda LIEI
 \begin{pseudocode}
 df = lambda inst_tyvars
        lambda LIEI

-        let Bop1
-            Bop2
-            ...
-            Bopn
-        and dbinds_super
-             in <op1,op2,...,opn,sd1,...,sdm>
+         let Bop1
+             Bop2
+             ...
+             Bopn
+         and dbinds_super
+              in <op1,op2,...,opn,sd1,...,sdm>

 \end{pseudocode}
 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
 \end{pseudocode}
 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.

@@ -125,95 +123,99 @@ and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
 
 
 %************************************************************************
 
 
 %************************************************************************

-%*                                                                     *
+%*                                                                      *

 \subsection{Extracting instance decls}
 \subsection{Extracting instance decls}

-%*                                                                     *
+%*                                                                      *

 %************************************************************************
 
 Gather up the instance declarations from their various sources
 
 \begin{code}
 %************************************************************************
 
 Gather up the instance declarations from their various sources
 
 \begin{code}

-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
+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 Name],     -- Source-code instance decls to process;
+                                -- contains all dfuns for this module
+           HsValBinds Name)     -- Supporting bindings for derived instances

 
 tcInstDecls1 tycl_decls inst_decls deriv_decls
   = checkNoErrs $
     do {        -- Stop if addInstInfos etc discovers any errors
 
 tcInstDecls1 tycl_decls inst_decls deriv_decls
   = checkNoErrs $
     do {        -- Stop if addInstInfos etc discovers any errors

-               -- (they recover, so that we get more than one error each
-               -- round) 
+                -- (they recover, so that we get more than one error each
+                -- round)

 
 

-               -- (1) Do class and family instance declarations
+                -- (1) Do class and family instance declarations

        ; let { idxty_decls = filter (isFamInstDecl . unLoc) tycl_decls }
        ; let { idxty_decls = filter (isFamInstDecl . unLoc) tycl_decls }

-       ; local_info_tycons <- mappM tcLocalInstDecl1  inst_decls
-       ; idx_tycons        <- mappM tcIdxTyInstDeclTL idxty_decls
+       ; local_info_tycons <- mapM tcLocalInstDecl1  inst_decls
+       ; idx_tycons        <- mapM tcIdxTyInstDeclTL idxty_decls

 
        ; let { (local_infos,
 
        ; 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
+                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 {
 
        ; tcExtendGlobalEnv (at_idx_tycon ++ implicit_things) $ do {
 

-               -- (3) Instances from generic class declarations
+                -- (3) Instances from generic class declarations

        ; generic_inst_info <- getGenericInstances clas_decls
 
        ; 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
+                -- 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 {
 
        ; 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
+                -- (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

                 -- NB: class instance declarations can contain derivings as
                 --     part of associated data type declarations
                 -- NB: class instance declarations can contain derivings as
                 --     part of associated data type declarations

-       ; (deriv_inst_info, deriv_binds) <- tcDeriving tycl_decls inst_decls 
+        failIfErrsM            -- If the addInsts stuff gave any errors, don't
+                               -- try the deriving stuff, becuase that may give
+                               -- more errors still
+       ; (deriv_inst_info, deriv_binds) <- tcDeriving tycl_decls inst_decls

                                                       deriv_decls
        ; addInsts deriv_inst_info   $ do {
 
        ; gbl_env <- getGblEnv
                                                       deriv_decls
        ; addInsts deriv_inst_info   $ do {
 
        ; gbl_env <- getGblEnv

-       ; returnM (gbl_env, 
-                 generic_inst_info ++ deriv_inst_info ++ local_info,
-                 deriv_binds) 
+       ; return (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,
     }}}}}}
   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.
+    --          too.

     tcIdxTyInstDeclTL ldecl@(L loc decl) =
       do { tything <- tcFamInstDecl ldecl
     tcIdxTyInstDeclTL ldecl@(L loc decl) =
       do { tything <- tcFamInstDecl ldecl

-        ; setSrcSpan loc $
-            when (isAssocFamily tything) $
-              addErr $ assocInClassErr (tcdName decl)
-        ; return tything
-        }
+         ; 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?!?"
     isAssocFamily (Just (ATyCon tycon)) =
       case tyConFamInst_maybe tycon of
         Nothing       -> panic "isAssocFamily: no family?!?"

-       Just (fam, _) -> isTyConAssoc fam
-    isAssocFamily (Just _            ) = panic "isAssocFamily: no tycon?!?"
+        Just (fam, _) -> isTyConAssoc fam
+    isAssocFamily (Just _             ) = panic "isAssocFamily: no tycon?!?"

     isAssocFamily Nothing               = False
 
     isAssocFamily Nothing               = False
 

-assocInClassErr name = 
-  ptext SLIT("Associated type") <+> quotes (ppr name) <+> 
-  ptext SLIT("must be inside a class instance")
+assocInClassErr :: Name -> SDoc
+assocInClassErr name =
+  ptext (sLit "Associated type") <+> quotes (ppr name) <+>
+  ptext (sLit "must be inside a class instance")

 
 

-addInsts :: [InstInfo] -> TcM a -> TcM a
+addInsts :: [InstInfo Name] -> TcM a -> TcM a

 addInsts infos thing_inside
   = tcExtendLocalInstEnv (map iSpec infos) thing_inside
 
 addInsts infos thing_inside
   = tcExtendLocalInstEnv (map iSpec infos) thing_inside
 

@@ -222,554 +224,542 @@ addFamInsts tycons thing_inside
   = tcExtendLocalFamInstEnv (map mkLocalFamInstTyThing tycons) thing_inside
   where
     mkLocalFamInstTyThing (ATyCon tycon) = mkLocalFamInst tycon
   = tcExtendLocalFamInstEnv (map mkLocalFamInstTyThing tycons) thing_inside
   where
     mkLocalFamInstTyThing (ATyCon tycon) = mkLocalFamInst tycon

-    mkLocalFamInstTyThing tything       = pprPanic "TcInstDcls.addFamInsts"
-                                                   (ppr tything)
+    mkLocalFamInstTyThing tything        = pprPanic "TcInstDcls.addFamInsts"
+                                                    (ppr tything)

 \end{code}
 
 \begin{code}
 \end{code}
 
 \begin{code}

-tcLocalInstDecl1 :: LInstDecl Name 
-                -> 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
-tcLocalInstDecl1 decl@(L loc (InstDecl poly_ty binds uprags ats))
-  =    -- Prime error recovery, set source location
-    recoverM (returnM ([], []))                $
-    setSrcSpan loc                     $
-    addErrCtxt (instDeclCtxt1 poly_ty) $
-
-    do { is_boot <- tcIsHsBoot
-       ; checkTc (not is_boot || (isEmptyLHsBinds binds && null uprags))
-                 badBootDeclErr
-
-       ; (tyvars, theta, tau) <- tcHsInstHead poly_ty
-       
-       -- Next, process any associated types.
-       ; idx_tycons <- mappM tcFamInstDecl ats
-
-       -- Now, check the validity of the instance.
-       ; (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 loc
-       ; overlap_flag <- getOverlapFlag
-       ; let (eq_theta,dict_theta) = partition isEqPred theta
+tcLocalInstDecl1 :: LInstDecl Name
+                 -> TcM ([InstInfo Name], [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
+tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats))
+  = -- Prime error recovery, set source location
+    recoverM (return ([], []))          $
+    setSrcSpan loc                     $
+    addErrCtxt (instDeclCtxt1 poly_ty)  $
+
+    do  { is_boot <- tcIsHsBoot
+        ; checkTc (not is_boot || (isEmptyLHsBinds binds && null uprags))
+                  badBootDeclErr
+
+        ; (tyvars, theta, tau) <- tcHsInstHead poly_ty
+
+        -- Next, process any associated types.
+        ; idx_tycons <- mapM tcFamInstDecl ats
+
+        -- Now, check the validity of the instance.
+        ; (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 (getLoc poly_ty)
+               -- Dfun location is that of instance *header*
+        ; overlap_flag <- getOverlapFlag
+        ; let (eq_theta,dict_theta) = partition isEqPred theta

               theta'         = eq_theta ++ dict_theta
               dfun           = mkDictFunId dfun_name tyvars theta' clas inst_tys
               theta'         = eq_theta ++ dict_theta
               dfun           = mkDictFunId dfun_name tyvars theta' clas inst_tys

-             ispec          = mkLocalInstance dfun overlap_flag
+              ispec          = mkLocalInstance dfun overlap_flag

 
 

-       ; return ([InstInfo { iSpec  = ispec, 
-                             iBinds = VanillaInst binds uprags }],
-                 catMaybes idx_tycons)
+        ; 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
         }
   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 ()
+                            -> ([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
     checkValidAndMissingATs clas inst_tys ats
       = do { -- Issue a warning for each class AT that is not defined in this

-            -- instance.
-          ; let class_ats   = map tyConName (classATs clas)
+             -- instance.
+           ; let class_ats   = map tyConName (classATs clas)

                  defined_ats = listToNameSet . map (tcdName.unLoc.fst)  $ ats
                  defined_ats = listToNameSet . map (tcdName.unLoc.fst)  $ ats

-                omitted     = filterOut (`elemNameSet` defined_ats) class_ats
-          ; warn <- doptM Opt_WarnMissingMethods
-          ; mapM_ (warnTc warn . omittedATWarn) 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)) = 
+                 omitted     = filterOut (`elemNameSet` defined_ats) class_ats
+           ; warn <- doptM Opt_WarnMissingMethods
+           ; mapM_ (warnTc warn . omittedATWarn) 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 _    _        (_, 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!
 -- !!!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' 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
     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 
+        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
       | isTyVarTy ty         = return ()
       | otherwise            = addErrTc $ mustBeVarArgErr ty

-    checkIndex ty (Just instTy) 
+    checkIndex ty (Just instTy)

       | ty `tcEqType` instTy = return ()
       | otherwise            = addErrTc $ wrongATArgErr ty instTy
 
       | ty `tcEqType` instTy = return ()
       | otherwise            = addErrTc $ wrongATArgErr ty instTy
 

-    listToNameSet = addListToNameSet emptyNameSet 
+    listToNameSet = addListToNameSet emptyNameSet

 
     substSameTyVar []       _            = emptyTvSubst
 
     substSameTyVar []       _            = emptyTvSubst

-    substSameTyVar (tv:tvs) replacingTvs = 
+    substSameTyVar (tv:tvs) replacingTvs =

       let replacement = case find (tv `sameLexeme`) replacingTvs of
       let replacement = case find (tv `sameLexeme`) replacingTvs of

-                         Nothing  -> mkTyVarTy tv
-                         Just rtv -> mkTyVarTy rtv
+                        Nothing  -> mkTyVarTy tv
+                        Just rtv -> mkTyVarTy rtv

           --
           --

-          tv1 `sameLexeme` tv2 = 
-           nameOccName (tyVarName tv1) == nameOccName (tyVarName tv2)
+          tv1 `sameLexeme` tv2 =
+            nameOccName (tyVarName tv1) == nameOccName (tyVarName tv2)

       in
       extendTvSubst (substSameTyVar tvs replacingTvs) tv replacement
 \end{code}
 
 
 %************************************************************************
       in
       extendTvSubst (substSameTyVar tvs replacingTvs) tv replacement
 \end{code}
 
 
 %************************************************************************

-%*                                                                     *
+%*                                                                      *

 \subsection{Type-checking instance declarations, pass 2}
 \subsection{Type-checking instance declarations, pass 2}

-%*                                                                     *
+%*                                                                      *

 %************************************************************************
 
 \begin{code}
 %************************************************************************
 
 \begin{code}

-tcInstDecls2 :: [LTyClDecl Name] -> [InstInfo] 
-            -> TcM (LHsBinds Id, TcLclEnv)
--- (a) From each class declaration, 
---     generate any default-method bindings
+tcInstDecls2 :: [LTyClDecl Name] -> [InstInfo Name]
+             -> TcM (LHsBinds Id, TcLclEnv)
+-- (a) From each class declaration,
+--      generate any default-method bindings

 -- (b) From each instance decl
 -- (b) From each instance decl

---     generate the dfun binding
+--      generate the dfun binding

 
 tcInstDecls2 tycl_decls inst_decls
 
 tcInstDecls2 tycl_decls inst_decls

-  = do {       -- (a) Default methods from class decls
-         (dm_binds_s, dm_ids_s) <- mapAndUnzipM tcClassDecl2 $
-                                   filter (isClassDecl.unLoc) tycl_decls
-       ; tcExtendIdEnv (concat dm_ids_s)       $ do 
-    
-               -- (b) instance declarations
-       ; inst_binds_s <- mappM tcInstDecl2 inst_decls
-
-               -- Done
-       ; let binds = unionManyBags dm_binds_s `unionBags` 
-                     unionManyBags inst_binds_s
-       ; tcl_env <- getLclEnv          -- Default method Ids in here
-       ; returnM (binds, tcl_env) }
+  = do  { -- (a) Default methods from class decls
+          (dm_binds_s, dm_ids_s) <- mapAndUnzipM tcClassDecl2 $
+                                    filter (isClassDecl.unLoc) tycl_decls
+        ; tcExtendIdEnv (concat dm_ids_s) $ do
+
+          -- (b) instance declarations
+        ; inst_binds_s <- mapM tcInstDecl2 inst_decls
+
+          -- Done
+        ; let binds = unionManyBags dm_binds_s `unionBags`
+                      unionManyBags inst_binds_s
+        ; tcl_env <- getLclEnv -- Default method Ids in here
+        ; return (binds, tcl_env) }

 \end{code}
 
 \end{code}
 

-======= New documentation starts here (Sept 92)         ==============
+======= New documentation starts here (Sept 92) ==============

 
 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
 
 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines

-the dictionary function for this instance declaration. For example
-\begin{verbatim}
-       instance Foo a => Foo [a] where
-               op1 x = ...
-               op2 y = ...
-\end{verbatim}
+the dictionary function for this instance declaration. For example
+
+        instance Foo a => Foo [a] where
+                op1 x = ...
+                op2 y = ...
+

 might generate something like
 might generate something like

-\begin{verbatim}
-       dfun.Foo.List dFoo_a = let op1 x = ...
-                                  op2 y = ...
-                              in
-                                  Dict [op1, op2]
-\end{verbatim}
+
+        dfun.Foo.List dFoo_a = let op1 x = ...
+                                   op2 y = ...
+                               in
+                                   Dict [op1, op2]

 
 HOWEVER, if the instance decl has no context, then it returns a
 bigger @HsBinds@ with declarations for each method.  For example
 
 HOWEVER, if the instance decl has no context, then it returns a
 bigger @HsBinds@ with declarations for each method.  For example

-\begin{verbatim}
-       instance Foo [a] where
-               op1 x = ...
-               op2 y = ...
-\end{verbatim}
+
+        instance Foo [a] where
+                op1 x = ...
+                op2 y = ...
+

 might produce
 might produce

-\begin{verbatim}
-       dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
-       const.Foo.op1.List a x = ...
-       const.Foo.op2.List a y = ...
-\end{verbatim}
+
+        dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
+        const.Foo.op1.List a x = ...
+        const.Foo.op2.List a y = ...
+

 This group may be mutually recursive, because (for example) there may
 be no method supplied for op2 in which case we'll get
 This group may be mutually recursive, because (for example) there may
 be no method supplied for op2 in which case we'll get

-\begin{verbatim}
-       const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
-\end{verbatim}
-that is, the default method applied to the dictionary at this type.

 
 

+        const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
+
+that is, the default method applied to the dictionary at this type.

 What we actually produce in either case is:
 
 What we actually produce in either case is:
 

-       AbsBinds [a] [dfun_theta_dicts]
-                [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
-                { d = (sd1,sd2, ..., op1, op2, ...)
-                  op1 = ...
-                  op2 = ...
-                }
+        AbsBinds [a] [dfun_theta_dicts]
+                 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
+                 { d = (sd1,sd2, ..., op1, op2, ...)
+                   op1 = ...
+                   op2 = ...
+                 }

 
 The "maybe" says that we only ask AbsBinds to make global constant methods
 if the dfun_theta is empty.
 
 
 The "maybe" says that we only ask AbsBinds to make global constant methods
 if the dfun_theta is empty.
 

-               

 For an instance declaration, say,
 
 For an instance declaration, say,
 

-       instance (C1 a, C2 b) => C (T a b) where
-               ...
+        instance (C1 a, C2 b) => C (T a b) where
+                ...

 
 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
 function whose type is
 
 
 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
 function whose type is
 

-       (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
+        (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)

 
 Notice that we pass it the superclass dictionaries at the instance type; this
 is the ``Mark Jones optimisation''.  The stuff before the "=>" here
 is the @dfun_theta@ below.
 
 
 Notice that we pass it the superclass dictionaries at the instance type; this
 is the ``Mark Jones optimisation''.  The stuff before the "=>" here
 is the @dfun_theta@ below.
 

-First comes the easy case of a non-local instance decl.
-

 
 \begin{code}
 
 \begin{code}

-tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)
+tcInstDecl2 :: InstInfo Name -> TcM (LHsBinds Id)

 -- Returns a binding for the dfun
 
 ------------------------
 -- Derived newtype instances; surprisingly tricky!
 --
 -- 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 )
+--      class Show a => Foo a b where ...
+--      newtype N a = MkN (Tree [a]) deriving( Foo Int )
+--

 -- The newtype gives an FC axiom looking like
 -- The newtype gives an FC axiom looking like

---     axiom CoT a ::  T a :=: Tree [a]
+--      axiom CoN a ::  N a :=: Tree [a]

 --   (see Note [Newtype coercions] in TyCon for this unusual form of axiom)
 --
 --   (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
+-- So all need is to generate a binding looking like:
+--      dfunFooT :: forall a. (Foo Int (Tree [a], Show (N a)) => Foo Int (N a)
+--      dfunFooT = /\a. \(ds:Show (N a)) (df:Foo (Tree [a])).
+--                case df `cast` (Foo Int (sym (CoN 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
 
 --
 -- 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)
+tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = NewTypeDerived })
+  = 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

 
 

-       ; 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)) }
+        ; let (cls, cls_inst_tys) = tcSplitDFunHead inst_head_ty
+              (class_tyvars, sc_theta, _, _) = classBigSig cls
+              cls_tycon = classTyCon cls
+              sc_theta' = substTheta (zipOpenTvSubst class_tyvars cls_inst_tys) sc_theta
+
+              Just (initial_cls_inst_tys, last_ty) = snocView cls_inst_tys
+              (nt_tycon, tc_args) = tcSplitTyConApp last_ty     -- Can't fail
+              rep_ty              = newTyConInstRhs nt_tycon tc_args
+
+              rep_pred     = mkClassPred cls (initial_cls_inst_tys ++ [rep_ty])
+                                -- In our example, rep_pred is (Foo Int (Tree [a]))
+              the_coercion = make_coercion cls_tycon initial_cls_inst_tys nt_tycon tc_args
+                                -- Coercion of kind (Foo Int (Tree [a]) ~ Foo Int (N a)
+
+        ; inst_loc   <- getInstLoc origin
+        ; sc_loc     <- getInstLoc InstScOrigin
+        ; dfun_dicts <- newDictBndrs inst_loc theta
+        ; sc_dicts   <- newDictBndrs sc_loc sc_theta'
+        ; this_dict  <- newDictBndr inst_loc (mkClassPred cls cls_inst_tys)
+        ; rep_dict   <- newDictBndr inst_loc rep_pred
+
+        -- Figure out bindings for the superclass context from dfun_dicts
+        -- Don't include this_dict in the 'givens', else
+        -- wanted_sc_insts get bound by just selecting from this_dict!!
+        ; sc_binds <- addErrCtxt superClassCtxt $
+                      tcSimplifySuperClasses inst_loc dfun_dicts (rep_dict:sc_dicts)
+
+        ; let coerced_rep_dict = mkHsWrap the_coercion (HsVar (instToId rep_dict))
+
+        ; body <- make_body cls_tycon cls_inst_tys sc_dicts coerced_rep_dict
+        ; let dict_bind = noLoc $ VarBind (instToId this_dict) (noLoc body)
+
+        ; return (unitBag $ noLoc $
+                  AbsBinds  tvs (map instToVar dfun_dicts)
+                            [(tvs, dfun_id, instToId this_dict, [])]
+                            (dict_bind `consBag` sc_binds)) }

   where
   where

-

       -----------------------
       -----------------------

-      --       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
+      --        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)))
       -- 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
+      --        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
 
       -- 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
+    make_coercion cls_tycon initial_cls_inst_tys nt_tycon tc_args
+        | Just co_con <- newTyConCo_maybe nt_tycon
+        , let co = mkSymCoercion (mkTyConApp co_con tc_args)
+        = WpCast (mkTyConApp cls_tycon (initial_cls_inst_tys ++ [co]))
+        | otherwise     -- The newtype is transparent; no need for a cast

         = idHsWrapper
 
       -----------------------
         = 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
+      --     (make_body C tys scs coreced_rep_dict)
+      --                returns
+      --     (case coerced_rep_dict of { C _ ops -> C scs ops })
+      -- But if there are no superclasses, it returns just coerced_rep_dict
+      -- See Note [Newtype deriving superclasses] in TcDeriv.lhs
+
+    make_body cls_tycon cls_inst_tys sc_dicts coerced_rep_dict
+        | null sc_dicts         -- 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
+          sc_dict_ids  = map instToId sc_dicts
+          pat_ty       = mkTyConApp cls_tycon cls_inst_tys

           cls_data_con = head (tyConDataCons cls_tycon)
           cls_data_con = head (tyConDataCons cls_tycon)

-          cls_arg_tys  = dataConInstArgTys cls_data_con cls_inst_tys 
+          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 })
           op_tys       = dropList sc_dict_ids cls_arg_tys
 
 ------------------------
 -- Ordinary instances
 
 tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = VanillaInst monobinds uprags })

-  = let 
-       dfun_id    = instanceDFunId ispec
-       rigid_info = InstSkol
-       inst_ty    = idType dfun_id
-       loc        = srcLocSpan (getSrcLoc dfun_id)
+  = let
+        dfun_id    = instanceDFunId ispec
+        rigid_info = InstSkol
+        inst_ty    = idType dfun_id
+        loc        = getSrcSpan dfun_id

     in
     in

-        -- Prime error recovery
-    recoverM (returnM emptyLHsBinds)           $
-    setSrcSpan loc                             $
-    addErrCtxt (instDeclCtxt2 (idType dfun_id))        $
-
-       -- Instantiate the instance decl with skolem constants 
-    tcSkolSigType rigid_info inst_ty   `thenM` \ (inst_tyvars', dfun_theta', inst_head') ->
-               -- These inst_tyvars' scope over the 'where' part
-               -- Those tyvars are inside the dfun_id's type, which is a bit
-               -- bizarre, but OK so long as you realise it!
+         -- Prime error recovery
+    recoverM (return emptyLHsBinds)             $
+    setSrcSpan loc                              $
+    addErrCtxt (instDeclCtxt2 (idType dfun_id)) $ do
+
+        -- Instantiate the instance decl with skolem constants
+    (inst_tyvars', dfun_theta', inst_head') <- tcSkolSigType rigid_info inst_ty
+                -- These inst_tyvars' scope over the 'where' part
+                -- Those tyvars are inside the dfun_id's type, which is a bit
+                -- bizarre, but OK so long as you realise it!

     let
     let

-       (clas, inst_tys') = tcSplitDFunHead inst_head'
+        (clas, inst_tys') = tcSplitDFunHead inst_head'

         (class_tyvars, sc_theta, _, op_items) = classBigSig clas
 
         -- Instantiate the super-class context with inst_tys
         (class_tyvars, sc_theta, _, op_items) = classBigSig clas
 
         -- Instantiate the super-class context with inst_tys

-       sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys') sc_theta
-       (eq_sc_theta',dict_sc_theta')     = partition isEqPred sc_theta'
-       origin    = SigOrigin rigid_info
-       (eq_dfun_theta',dict_dfun_theta') = partition isEqPred dfun_theta'
-    in
-        -- Create dictionary Ids from the specified instance contexts.
-    getInstLoc InstScOrigin                            `thenM` \ sc_loc -> 
-    newDictBndrs sc_loc dict_sc_theta'                 `thenM` \ sc_dicts ->
-    getInstLoc origin                                  `thenM` \ inst_loc -> 
-    mkMetaCoVars eq_sc_theta'                          `thenM` \ sc_covars ->
-    mkEqInsts eq_sc_theta' (map mkWantedCo sc_covars)  `thenM` \ wanted_sc_eqs ->
-    mkCoVars eq_dfun_theta'                            `thenM` \ dfun_covars ->
-    mkEqInsts eq_dfun_theta' (map mkGivenCo $ mkTyVarTys dfun_covars)  `thenM` \ dfun_eqs    ->
-    newDictBndrs inst_loc dict_dfun_theta'             `thenM` \ dfun_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.
-
-       -- Typecheck the methods
-    let                -- These insts are in scope; quite a few, eh?
-       dfun_insts      = dfun_eqs ++ dfun_dicts
-       wanted_sc_insts = wanted_sc_eqs   ++ sc_dicts
-       given_sc_eqs    = map (updateEqInstCoercion (mkGivenCo . TyVarTy . fromWantedCo "tcInstDecl2") ) wanted_sc_eqs
-       given_sc_insts  = given_sc_eqs   ++ sc_dicts
-       avail_insts     = [this_dict] ++ dfun_insts ++ given_sc_insts
-    in
-    tcMethods origin clas inst_tyvars' 
-             dfun_theta' inst_tys' avail_insts 
-             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
-       -- wanted_sc_insts get bound by just selecting  from this_dict!!
-    addErrCtxt superClassCtxt
-       (tcSimplifySuperClasses inst_loc
-                        dfun_insts wanted_sc_insts)    `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 
-    tcPrags dfun_id (filter isSpecInstLSig uprags)     `thenM` \ prags -> 
-    
-       -- Create the result bindings
+        sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys') sc_theta
+        (eq_sc_theta',dict_sc_theta')     = partition isEqPred sc_theta'
+        origin    = SigOrigin rigid_info
+        (eq_dfun_theta',dict_dfun_theta') = partition isEqPred dfun_theta'
+
+         -- Create dictionary Ids from the specified instance contexts.
+    sc_loc        <- getInstLoc InstScOrigin
+    sc_dicts      <- newDictBndrs sc_loc dict_sc_theta'
+    inst_loc      <- getInstLoc origin
+    sc_covars     <- mkMetaCoVars eq_sc_theta'
+    wanted_sc_eqs <- mkEqInsts eq_sc_theta' (map mkWantedCo sc_covars)
+    dfun_covars   <- mkCoVars eq_dfun_theta'
+    dfun_eqs      <- mkEqInsts eq_dfun_theta' (map mkGivenCo $ mkTyVarTys dfun_covars)
+    dfun_dicts    <- newDictBndrs inst_loc dict_dfun_theta'
+    this_dict     <- newDictBndr inst_loc (mkClassPred clas inst_tys')
+                -- Default-method Ids may be mentioned in synthesised RHSs,
+                -- but they'll already be in the environment.
+
+        -- Typecheck the methods
+    let -- These insts are in scope; quite a few, eh?
+        dfun_insts      = dfun_eqs ++ dfun_dicts
+        wanted_sc_insts = wanted_sc_eqs   ++ sc_dicts
+        given_sc_eqs    = map (updateEqInstCoercion (mkGivenCo . TyVarTy . fromWantedCo "tcInstDecl2") ) wanted_sc_eqs
+        given_sc_insts  = given_sc_eqs   ++ sc_dicts
+        avail_insts     = dfun_insts ++ given_sc_insts
+
+    (meth_ids, meth_binds) <- tcMethods origin clas inst_tyvars'
+                                 dfun_theta' inst_tys' this_dict avail_insts
+                                 op_items monobinds uprags
+
+    -- Figure out bindings for the superclass context
+    -- Don't include this_dict in the 'givens', else
+    -- wanted_sc_insts get bound by just selecting  from this_dict!!
+    sc_binds <- addErrCtxt superClassCtxt
+                   (tcSimplifySuperClasses inst_loc dfun_insts wanted_sc_insts)
+
+    -- It's possible that the superclass stuff might unified one
+    -- of the inst_tyavars' with something in the envt
+    checkSigTyVars inst_tyvars'
+
+    -- Deal with 'SPECIALISE instance' pragmas
+    prags <- tcPrags dfun_id (filter isSpecInstLSig uprags)
+
+    -- Create the result bindings

     let
         dict_constr   = classDataCon clas
     let
         dict_constr   = classDataCon clas

-       scs_and_meths = map instToId sc_dicts ++ meth_ids
-       this_dict_id  = instToId this_dict
-       inline_prag | null dfun_insts  = []
-                   | otherwise        = [L loc (InlinePrag (Inline AlwaysActive True))]
-               -- Always inline the dfun; this is an experimental decision
-               -- because it makes a big performance difference sometimes.
-               -- Often it means we can do the method selection, and then
-               -- inline the method as well.  Marcin's idea; see comments below.
-               --
-               -- BUT: don't inline it if it's a constant dictionary;
-               -- we'll get all the benefit without inlining, and we get
-               -- a **lot** of code duplication if we inline it
-               --
-               --      See Note [Inline dfuns] below
-
-       dict_rhs
-         = mkHsConApp dict_constr (inst_tys' ++ mkTyVarTys sc_covars)  (map HsVar scs_and_meths)
-               -- We don't produce a binding for the dict_constr; instead we
-               -- rely on the simplifier to unfold this saturated application
-               -- We do this rather than generate an HsCon directly, because
-               -- it means that the special cases (e.g. dictionary with only one
-               -- member) are dealt with by the common MkId.mkDataConWrapId code rather
-               -- than needing to be repeated here.
-
-       dict_bind  = noLoc (VarBind this_dict_id dict_rhs)
-       all_binds  = dict_bind `consBag` (sc_binds `unionBags` meth_binds)
-
-       main_bind = noLoc $ AbsBinds
-                           (inst_tyvars' ++ dfun_covars)
-                           (map instToId dfun_dicts)
-                           [(inst_tyvars' ++ dfun_covars, dfun_id, this_dict_id, inline_prag ++ prags)] 
-                           all_binds
-    in
-    showLIE (text "instance")          `thenM_`
-    returnM (unitBag main_bind)
+        scs_and_meths = map instToId sc_dicts ++ meth_ids
+        this_dict_id  = instToId this_dict
+        inline_prag | null dfun_insts  = []
+                    | otherwise        = [L loc (InlinePrag (Inline AlwaysActive True))]
+                -- Always inline the dfun; this is an experimental decision
+                -- because it makes a big performance difference sometimes.
+                -- Often it means we can do the method selection, and then
+                -- inline the method as well.  Marcin's idea; see comments below.
+                --
+                -- BUT: don't inline it if it's a constant dictionary;
+                -- we'll get all the benefit without inlining, and we get
+                -- a **lot** of code duplication if we inline it
+                --
+                --      See Note [Inline dfuns] below
+
+        dict_rhs = mkHsConApp dict_constr (inst_tys' ++ mkTyVarTys sc_covars)
+                                          (map HsVar scs_and_meths)
+                -- We don't produce a binding for the dict_constr; instead we
+                -- rely on the simplifier to unfold this saturated application
+                -- We do this rather than generate an HsCon directly, because
+                -- it means that the special cases (e.g. dictionary with only one
+                -- member) are dealt with by the common MkId.mkDataConWrapId code rather
+                -- than needing to be repeated here.
+
+        dict_bind  = noLoc (VarBind this_dict_id dict_rhs)
+        all_binds  = dict_bind `consBag` (sc_binds `unionBags` meth_binds)
+
+        main_bind = noLoc $ AbsBinds
+                            (inst_tyvars' ++ dfun_covars)
+                            (map instToId dfun_dicts)
+                            [(inst_tyvars' ++ dfun_covars, dfun_id, this_dict_id, inline_prag ++ prags)]
+                            all_binds
+
+    showLIE (text "instance")
+    return (unitBag main_bind)

 
 mkCoVars :: [PredType] -> TcM [TyVar]
 
 mkCoVars :: [PredType] -> TcM [TyVar]

-mkCoVars [] = return []
-mkCoVars (pred:preds) = 
-       do { uniq <- newUnique
-          ; let name = mkSysTvName uniq FSLIT("mkCoVars")
-          ; let tv = mkCoVar name (PredTy pred)
-          ; tvs <- mkCoVars preds
-          ; return (tv:tvs)
-          }
+mkCoVars = newCoVars . map unEqPred
+  where
+    unEqPred (EqPred ty1 ty2) = (ty1, ty2)
+    unEqPred _                = panic "TcInstDcls.mkCoVars"

 
 mkMetaCoVars :: [PredType] -> TcM [TyVar]
 
 mkMetaCoVars :: [PredType] -> TcM [TyVar]

-mkMetaCoVars [] = return []
-mkMetaCoVars (EqPred ty1 ty2:preds) = 
-       do { tv <- newMetaTyVar TauTv (mkCoKind ty1 ty2)          
-          ; tvs <- mkMetaCoVars preds
-          ; return (tv:tvs)
-          }
-
-
-tcMethods origin clas inst_tyvars' dfun_theta' inst_tys' 
-         avail_insts op_items monobinds uprags
-  =    -- Check that all the method bindings come from this class
+mkMetaCoVars = mapM eqPredToCoVar
+  where
+    eqPredToCoVar (EqPred ty1 ty2) = newMetaCoVar ty1 ty2
+    eqPredToCoVar _                = panic "TcInstDcls.mkMetaCoVars"
+
+tcMethods :: InstOrigin -> Class -> [TcTyVar] -> TcThetaType -> [TcType]
+          -> Inst -> [Inst] -> [(Id, DefMeth)] -> LHsBindsLR Name Name
+          -> [LSig Name]
+          -> TcM ([Id], Bag (LHsBind Id))
+tcMethods origin clas inst_tyvars' dfun_theta' inst_tys'
+          this_dict extra_insts op_items monobinds uprags = do
+    -- Check that all the method bindings come from this class

     let
     let

-       sel_names = [idName sel_id | (sel_id, _) <- op_items]
-       bad_bndrs = collectHsBindBinders monobinds `minusList` sel_names
-    in
-    mappM (addErrTc . badMethodErr clas) bad_bndrs     `thenM_`
+        sel_names = [idName sel_id | (sel_id, _) <- op_items]
+        bad_bndrs = collectHsBindBinders monobinds `minusList` sel_names
+
+    mapM (addErrTc . badMethodErr clas) bad_bndrs

 
 

-       -- Make the method bindings
+    -- Make the method bindings

     let
     let

-       mk_method_bind = mkMethodBind origin clas inst_tys' monobinds
-    in
-    mapAndUnzipM mk_method_bind op_items       `thenM` \ (meth_insts, meth_infos) ->
-
-       -- And type check them
-       -- It's really worth making meth_insts available to the tcMethodBind
-       -- Consider     instance Monad (ST s) where
-       --                {-# INLINE (>>) #-}
-       --                (>>) = ...(>>=)...
-       -- If we don't include meth_insts, we end up with bindings like this:
-       --      rec { dict = MkD then bind ...
-       --            then = inline_me (... (GHC.Base.>>= dict) ...)
-       --            bind = ... }
-       -- The trouble is that (a) 'then' and 'dict' are mutually recursive, 
-       -- and (b) the inline_me prevents us inlining the >>= selector, which
-       -- would unravel the loop.  Result: (>>) ends up as a loop breaker, and
-       -- is not inlined across modules. Rather ironic since this does not
-       -- happen without the INLINE pragma!  
-       --
-       -- Solution: make meth_insts available, so that 'then' refers directly
-       --           to the local 'bind' rather than going via the dictionary.
-       --
-       -- BUT WATCH OUT!  If the method type mentions the class variable, then
-       -- this optimisation is not right.  Consider
-       --      class C a where
-       --        op :: Eq a => a
-       --
-       --      instance C Int where
-       --        op = op
-       -- The occurrence of 'op' on the rhs gives rise to a constraint
-       --      op at Int
-       -- The trouble is that the 'meth_inst' for op, which is 'available', also
-       -- looks like 'op at Int'.  But they are not the same.
+        mk_method_id (sel_id, _) = mkMethId origin clas sel_id inst_tys'
+
+    (meth_insts, meth_ids) <- mapAndUnzipM mk_method_id op_items
+
+        -- And type check them
+        -- It's really worth making meth_insts available to the tcMethodBind
+        -- Consider     instance Monad (ST s) where
+        --                {-# INLINE (>>) #-}
+        --                (>>) = ...(>>=)...
+        -- If we don't include meth_insts, we end up with bindings like this:
+        --      rec { dict = MkD then bind ...
+        --            then = inline_me (... (GHC.Base.>>= dict) ...)
+        --            bind = ... }
+        -- The trouble is that (a) 'then' and 'dict' are mutually recursive,
+        -- and (b) the inline_me prevents us inlining the >>= selector, which
+        -- would unravel the loop.  Result: (>>) ends up as a loop breaker, and
+        -- is not inlined across modules. Rather ironic since this does not
+        -- happen without the INLINE pragma!
+        --
+        -- Solution: make meth_insts available, so that 'then' refers directly
+        --           to the local 'bind' rather than going via the dictionary.
+        --
+        -- BUT WATCH OUT!  If the method type mentions the class variable, then
+        -- this optimisation is not right.  Consider
+        --      class C a where
+        --        op :: Eq a => a
+        --
+        --      instance C Int where
+        --        op = op
+        -- The occurrence of 'op' on the rhs gives rise to a constraint
+        --      op at Int
+        -- The trouble is that the 'meth_inst' for op, which is 'available', also
+        -- looks like 'op at Int'.  But they are not the same.

     let
     let

-       prag_fn        = mkPragFun uprags
-       all_insts      = avail_insts ++ catMaybes meth_insts
-       sig_fn n       = Just []        -- No scoped type variables, but every method has
-                                       -- a type signature, in effect, so that we check
-                                       -- the method has the right type
-       tc_method_bind = tcMethodBind inst_tyvars' dfun_theta' all_insts sig_fn prag_fn
-       meth_ids       = [meth_id | (_,meth_id,_) <- meth_infos]
-    in
+        prag_fn        = mkPragFun uprags
+        all_insts      = extra_insts ++ catMaybes meth_insts
+        sig_fn _       = Just []        -- No scoped type variables, but every method has
+                                        -- a type signature, in effect, so that we check
+                                        -- the method has the right type
+        tc_method_bind = tcMethodBind origin inst_tyvars' dfun_theta' this_dict 
+                                     all_insts sig_fn prag_fn monobinds

 
 

-    mapM tc_method_bind meth_infos             `thenM` \ meth_binds_s ->
-   
-    returnM (meth_ids, unionManyBags meth_binds_s)
+    meth_binds_s <- zipWithM tc_method_bind op_items meth_ids
+
+    return (meth_ids, unionManyBags meth_binds_s)

 \end{code}
 
 
 \end{code}
 
 

-               ------------------------------
-       [Inline dfuns] Inlining dfuns unconditionally
-               ------------------------------
+                ------------------------------
+        [Inline dfuns] Inlining dfuns unconditionally
+                ------------------------------

 
 The code above unconditionally inlines dict funs.  Here's why.
 Consider this program:
 
 The code above unconditionally inlines dict funs.  Here's why.
 Consider this program:

@@ -782,49 +772,49 @@ This needs the (Eq (Int,Int)) instance.  If we inline that dfun
 the code we end up with is good:
 
     Test.$wtest =
 the code we end up with is good:
 
     Test.$wtest =

-       \r -> case ==# [ww ww1] of wild {
-               PrelBase.False -> Test.$wtest ww1 ww;
-               PrelBase.True ->
-                 case ==# [ww1 ww] of wild1 {
-                   PrelBase.False -> Test.$wtest ww1 ww;
-                   PrelBase.True -> PrelBase.True [];
-                 };
-           };
+        \r -> case ==# [ww ww1] of wild {
+                PrelBase.False -> Test.$wtest ww1 ww;
+                PrelBase.True ->
+                  case ==# [ww1 ww] of wild1 {
+                    PrelBase.False -> Test.$wtest ww1 ww;
+                    PrelBase.True -> PrelBase.True [];
+                  };
+            };

     Test.test = \r [w w1]
     Test.test = \r [w w1]

-           case w of w2 {
-             PrelBase.I# ww ->
-                 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
-           };
+            case w of w2 {
+              PrelBase.I# ww ->
+                  case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
+            };

 
 If we don't inline the dfun, the code is not nearly as good:
 
     (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
 
 If we don't inline the dfun, the code is not nearly as good:
 
     (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {

-             PrelBase.:DEq tpl1 tpl2 -> tpl2;
-           };
-    
+              PrelBase.:DEq tpl1 tpl2 -> tpl2;
+            };
+

     Test.$wtest =
     Test.$wtest =

-       \r [ww ww1]
-           let { y = PrelBase.I#! [ww1]; } in
-           let { x = PrelBase.I#! [ww]; } in
-           let { sat_slx = PrelTup.(,)! [y x]; } in
-           let { sat_sly = PrelTup.(,)! [x y];
-           } in
-             case == sat_sly sat_slx of wild {
-               PrelBase.False -> Test.$wtest ww1 ww;
-               PrelBase.True -> PrelBase.True [];
-             };
-    
+        \r [ww ww1]
+            let { y = PrelBase.I#! [ww1]; } in
+            let { x = PrelBase.I#! [ww]; } in
+            let { sat_slx = PrelTup.(,)! [y x]; } in
+            let { sat_sly = PrelTup.(,)! [x y];
+            } in
+              case == sat_sly sat_slx of wild {
+                PrelBase.False -> Test.$wtest ww1 ww;
+                PrelBase.True -> PrelBase.True [];
+              };
+

     Test.test =
     Test.test =

-       \r [w w1]
-           case w of w2 {
-             PrelBase.I# ww ->
-                 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
-           };
+        \r [w w1]
+            case w of w2 {
+              PrelBase.I# ww ->
+                  case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
+            };

 
 Why doesn't GHC inline $fEq?  Because it looks big:
 
     PrelTup.zdfEqZ1T{-rcX-}
 
 Why doesn't GHC inline $fEq?  Because it looks big:
 
     PrelTup.zdfEqZ1T{-rcX-}

-       = \ @ a{-reT-} :: * @ b{-reS-} :: *
+        = \ @ a{-reT-} :: * @ b{-reS-} :: *

             zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
             zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
             let {
             zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
             zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
             let {

@@ -836,21 +826,21 @@ Why doesn't GHC inline $fEq?  Because it looks big:
             let {
               zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
               zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
             let {
               zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
               zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})

-                              ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
-                            case ds{-rf5-}
-                            of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
-                            case ds1{-rf4-}
-                            of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
-                            PrelBase.zaza{-r4e-}
-                              (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
-                              (zeze{-rf0-} a2{-reZ-} b2{-reY-})
-                            }
-                            } } in     
+                               ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
+                             case ds{-rf5-}
+                             of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
+                             case ds1{-rf4-}
+                             of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
+                             PrelBase.zaza{-r4e-}
+                               (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
+                               (zeze{-rf0-} a2{-reZ-} b2{-reY-})
+                             }
+                             } } in

             let {
               a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
               a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
             let {
               a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
               a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})

-                           b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
-                         PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
+                            b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
+                          PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})

             } in
               PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
 
             } in
               PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
 

@@ -859,38 +849,45 @@ simplified: only zeze2 is extracted and its body is simplified.
 
 
 %************************************************************************
 
 
 %************************************************************************

-%*                                                                     *
+%*                                                                      *

 \subsection{Error messages}
 \subsection{Error messages}

-%*                                                                     *
+%*                                                                      *

 %************************************************************************
 
 \begin{code}
 %************************************************************************
 
 \begin{code}

-instDeclCtxt1 hs_inst_ty 
+instDeclCtxt1 :: LHsType Name -> SDoc
+instDeclCtxt1 hs_inst_ty

   = inst_decl_ctxt (case unLoc hs_inst_ty of
   = inst_decl_ctxt (case unLoc hs_inst_ty of

-                       HsForAllTy _ _ _ (L _ (HsPredTy pred)) -> ppr pred
-                       HsPredTy pred                    -> ppr pred
-                       other                            -> ppr hs_inst_ty)     -- Don't expect this
+                        HsForAllTy _ _ _ (L _ (HsPredTy pred)) -> ppr pred
+                        HsPredTy pred                    -> ppr pred
+                        _                                -> ppr hs_inst_ty)     -- Don't expect this
+instDeclCtxt2 :: Type -> SDoc

 instDeclCtxt2 dfun_ty
   = inst_decl_ctxt (ppr (mkClassPred cls tys))
   where
     (_,_,cls,tys) = tcSplitDFunTy dfun_ty
 
 instDeclCtxt2 dfun_ty
   = inst_decl_ctxt (ppr (mkClassPred cls tys))
   where
     (_,_,cls,tys) = tcSplitDFunTy dfun_ty
 

-inst_decl_ctxt doc = ptext SLIT("In the instance declaration for") <+> quotes doc
+inst_decl_ctxt :: SDoc -> SDoc
+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")
+superClassCtxt :: SDoc
+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)
+atInstCtxt :: Name -> SDoc
+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
+mustBeVarArgErr :: Type -> SDoc
+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 :: Type -> Type -> SDoc

 wrongATArgErr ty instTy =
 wrongATArgErr ty instTy =

-  sep [ ptext SLIT("Type indexes must match class instance head")
-      , ptext SLIT("Found") <+> ppr ty <+> ptext SLIT("but expected") <+>
+  sep [ ptext (sLit "Type indexes must match class instance head")
+      , ptext (sLit "Found") <+> ppr ty <+> ptext (sLit "but expected") <+>

          ppr instTy
       ]
 \end{code}
          ppr instTy
       ]
 \end{code}