- (case maybe_dfun_name of
- Nothing -> -- A source-file instance declaration
- -- Check for respectable instance type, and context
- -- but only do this for non-imported instance decls.
- -- Imported ones should have been checked already, and may indeed
- -- contain something illegal in normal Haskell, notably
- -- instance CCallable [Char]
- checkValidTheta InstThetaCtxt theta `thenTc_`
- checkValidInstHead tau `thenTc_`
- checkTc (checkInstFDs theta clas inst_tys)
- (instTypeErr (pprClassPred clas inst_tys) msg) `thenTc_`
- newDFunName clas inst_tys src_loc `thenTc` \ dfun_name ->
- returnTc (mkDictFunId dfun_name clas tyvars inst_tys theta)
-
- Just dfun_name -> -- An interface-file instance declaration
- -- Should be in scope by now, because we should
- -- have sucked in its interface-file definition
- -- So it will be replete with its unfolding etc
- tcLookupId dfun_name
- ) `thenNF_Tc` \ dfun_id ->
- returnTc [InstInfo { iDFunId = dfun_id, iBinds = binds, iPrags = uprags }]
- where
- msg = parens (ptext SLIT("the instance types do not agree with the functional dependencies of the class"))
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection{Extracting generic instance declaration from class declarations}
-%* *
-%************************************************************************
-
-@getGenericInstances@ extracts the generic instance declarations from a class
-declaration. For exmaple
-
- class C a where
- op :: a -> a
-
- op{ x+y } (Inl v) = ...
- op{ x+y } (Inr v) = ...
- op{ x*y } (v :*: w) = ...
- op{ 1 } Unit = ...
-
-gives rise to the instance declarations
-
- instance C (x+y) where
- op (Inl v) = ...
- op (Inr v) = ...
-
- instance C (x*y) where
- op (v :*: w) = ...
-
- instance C 1 where
- op Unit = ...
-
-
-\begin{code}
-getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
-getGenericInstances class_decls
- = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
- let
- gen_inst_info = concat gen_inst_infos
- in
- if null gen_inst_info then
- returnTc []
- else
- getDOptsTc `thenTc` \ dflags ->
- ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
- (vcat (map pprInstInfo gen_inst_info)))
- `thenNF_Tc_`
- returnTc gen_inst_info
-
-get_generics decl@(ClassDecl {tcdMeths = Nothing})
- = returnTc [] -- Imported class decls
-
-get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
- | null groups
- = returnTc [] -- The comon case: no generic default methods
-
- | otherwise -- A source class decl with generic default methods
- = recoverNF_Tc (returnNF_Tc []) $
- tcAddDeclCtxt decl $
- tcLookupClass class_name `thenTc` \ clas ->
-
- -- Make an InstInfo out of each group
- mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
-
- -- Check that there is only one InstInfo for each type constructor
- -- The main way this can fail is if you write
- -- f {| a+b |} ... = ...
- -- f {| x+y |} ... = ...
- -- Then at this point we'll have an InstInfo for each
- let
- tc_inst_infos :: [(TyCon, InstInfo)]
- tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
-
- bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
- group `lengthExceeds` 1]
- get_uniq (tc,_) = getUnique tc