--
-- We check for respectable instance type, and context
tcLocalInstDecl1 decl@(L loc (InstDecl poly_ty binds uprags ats))
+ -- !!!TODO: Handle the `ats' parameter!!! -=chak
= -- Prime error recovery, set source location
- ASSERT( null ats )
- -- !!!TODO: Handle the `ats' parameter!!! -=chak
recoverM (returnM Nothing) $
setSrcSpan loc $
addErrCtxt (instDeclCtxt1 poly_ty) $
\begin{code}
tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)
+-- Returns a binding for the dfun
-tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = binds })
+--
+-- Derived newtype instances
+--
+-- We need to make a copy of the dictionary we are deriving from
+-- because we may need to change some of the superclass dictionaries
+-- see Note [Newtype deriving superclasses] in TcDeriv.lhs
+--
+-- 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 :: Tree [a] = T a
+--
+-- So all need is to generate a binding looking like
+-- dfunFooT :: forall a. (Show (T a), Foo Int (Tree [a]) => Foo Int (T a)
+-- dfunFooT = /\a. \(ds:Show (T a)) (df:Foo (Tree [a])).
+-- case df `cast` (Foo Int (CoT a)) of
+-- Foo _ op1 .. opn -> Foo ds op1 .. opn
+
+tcInstDecl2 (InstInfo { iSpec = ispec,
+ iBinds = NewTypeDerived tycon rep_tys })
+ = do { let dfun_id = instanceDFunId ispec
+ rigid_info = InstSkol dfun_id
+ origin = SigOrigin rigid_info
+ inst_ty = idType dfun_id
+ maybe_co_con = newTyConCo tycon
+ ; (tvs, theta, inst_head) <- tcSkolSigType rigid_info inst_ty
+ ; rep_dict <- newDict origin (head theta)
+ ; if isSingleton theta then
+ return (unitBag (VarBind dfun_id $
+ case maybe_co_con of
+ Nothing -> rep_dict
+ Just co_con -> mkCoerce rep_dict $
+ mkAppCoercion (mkAppsCoercion tycon rep_tys)
+ (mkTyConApp co_con tvs)))
+ else do
+ let rep_dict_id = instToId rep_dict
+ coerced_dict = case maybe_co_con of
+ Nothing -> rep_dict_id
+ Just co_con -> mkCoerce rep_dict_id $
+ mkAppCoercion (mkAppsCoercion tycon rep_tys)
+ (mkTyConApp co_con tvs)
+ ; return (unitBag (VarBind dfun_id
+ co_fn = CoTyLams tvs <.> CoLams [rep_dict_id] <.> ExprCoFn cast
+
+ ; return (unitBag (VarBind dfun_id (HsCoerce co_fn (HsVar rep_dict_id))))
+
+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')
+
+
+
+tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = VanillaInst monobinds uprags })
= let
dfun_id = instanceDFunId ispec
rigid_info = InstSkol dfun_id
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
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 prags) `thenM` \ prags ->
-- Create the result bindings
let
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]
mapM tc_method_bind meth_infos `thenM` \ meth_binds_s ->
returnM (meth_ids, unionManyBags meth_binds_s)
+v v v v v v v
+*************
-- Derived newtype instances
tcMethods origin clas inst_tyvars' dfun_theta' inst_tys'
- avail_insts op_items (NewTypeDerived rep_tys)
+ avail_insts op_items (NewTypeDerived maybe_co rep_tys)
= getInstLoc origin `thenM` \ inst_loc ->
mapAndUnzip3M (do_one inst_loc) op_items `thenM` \ (meth_ids, meth_binds, rhs_insts) ->
-- 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}
projects / ghc-hetmet.git / blobdiff