%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1995
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[TcClassDcl]{Typechecking class declarations}
\begin{code}
+module TcClassDcl ( tcClassDecl1, tcClassDecls2,
+ tcMethodBind, badMethodErr
+ ) where
+
#include "HsVersions.h"
-module TcClassDcl (
- tcClassDecl1, tcClassDecls2
- ) where
+import HsSyn ( TyClDecl(..), Sig(..), MonoBinds(..),
+ HsExpr(..), HsLit(..), HsType(..), HsPred(..),
+ mkSimpleMatch, andMonoBinds, andMonoBindList,
+ isClassOpSig, isPragSig,
+ getClassDeclSysNames,
+ )
+import BasicTypes ( TopLevelFlag(..), RecFlag(..) )
+import RnHsSyn ( RenamedTyClDecl,
+ RenamedClassOpSig, RenamedMonoBinds,
+ RenamedContext, RenamedSig,
+ maybeGenericMatch
+ )
+import TcHsSyn ( TcMonoBinds )
+
+import Inst ( InstOrigin(..), LIE, emptyLIE, plusLIE, plusLIEs,
+ newDicts, newMethod )
+import TcEnv ( TcId, TcEnv, RecTcEnv, TyThingDetails(..), tcAddImportedIdInfo,
+ tcLookupClass, tcExtendTyVarEnvForMeths, tcExtendGlobalTyVars,
+ tcExtendLocalValEnv, tcExtendTyVarEnv
+ )
+import TcBinds ( tcBindWithSigs, tcSpecSigs )
+import TcMonoType ( tcHsRecType, tcRecClassContext, checkSigTyVars, checkAmbiguity, sigCtxt, mkTcSig )
+import TcSimplify ( tcSimplifyAndCheck, bindInstsOfLocalFuns )
+import TcType ( TcType, TcTyVar, tcInstTyVars, zonkTcSigTyVars )
+import TcMonad
+import Generics ( mkGenericRhs, validGenericMethodType )
+import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
+import Class ( classTyVars, classBigSig, classTyCon,
+ Class, ClassOpItem, DefMeth (..) )
+import MkId ( mkDictSelId, mkDataConId, mkDataConWrapId, mkDefaultMethodId )
+import DataCon ( mkDataCon, notMarkedStrict )
+import Id ( Id, idType, idName )
+import Module ( Module )
+import Name ( Name, NamedThing(..) )
+import Name ( NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv, nameEnvElts )
+import NameSet ( emptyNameSet )
+import Outputable
+import Type ( Type, ClassContext, mkTyVarTys, mkDictTys, mkClassPred,
+ splitTyConApp_maybe, isTyVarTy
+ )
+import Var ( TyVar )
+import VarSet ( mkVarSet, emptyVarSet )
+import CmdLineOpts
+import ErrUtils ( dumpIfSet )
+import Util ( count )
+import Maybes ( seqMaybe, maybeToBool )
+\end{code}
-import Ubiq
-import HsSyn ( ClassDecl(..), HsBinds(..), Bind(..), MonoBinds(..),
- Match(..), GRHSsAndBinds(..), GRHS(..), HsExpr(..),
- HsLit(..), OutPat(..), Sig(..), PolyType(..), MonoType,
- Stmt, Qual, ArithSeqInfo, InPat, Fake )
-import HsPragmas ( ClassPragmas(..) )
-import RnHsSyn ( RenamedClassDecl(..), RenamedClassPragmas(..),
- RenamedClassOpSig(..), RenamedMonoBinds(..),
- RenamedGenPragmas(..), RenamedContext(..) )
-import TcHsSyn ( TcIdOcc(..), TcHsBinds(..), TcMonoBinds(..), TcExpr(..),
- mkHsTyApp, mkHsTyLam, mkHsDictApp, mkHsDictLam, unZonkId )
-import TcMonad
-import Inst ( Inst, InstOrigin(..), LIE(..), emptyLIE, plusLIE, newDicts )
-import TcEnv ( tcLookupClass, tcLookupTyVar, tcLookupTyCon, newLocalIds)
-import TcInstDcls ( processInstBinds )
-import TcKind ( unifyKind )
-import TcMonoType ( tcMonoType, tcContext )
-import TcType ( TcType(..), TcTyVar(..), tcInstType, tcInstSigTyVars )
-import TcKind ( TcKind )
-
-import Bag ( foldBag )
-import Class ( GenClass, mkClass, mkClassOp, getClassBigSig,
- getClassOps, getClassOpString, getClassOpLocalType )
-import CoreUtils ( escErrorMsg )
-import Id ( mkSuperDictSelId, mkMethodSelId, mkDefaultMethodId,
- idType )
-import IdInfo ( noIdInfo )
-import Name ( Name, getNameFullName, getTagFromClassOpName )
-import PrelVals ( pAT_ERROR_ID )
-import PprStyle
-import Pretty
-import PprType ( GenType, GenTyVar, GenClassOp )
-import SpecEnv ( SpecEnv(..) )
-import SrcLoc ( mkGeneratedSrcLoc )
-import Type ( mkFunTy, mkTyVarTy, mkTyVarTys, mkDictTy,
- mkForAllTy, mkSigmaTy, splitSigmaTy)
-import TysWiredIn ( stringTy )
-import TyVar ( GenTyVar )
-import Unique ( Unique )
-import Util
-
--- import TcPragmas ( tcGenPragmas, tcClassOpPragmas )
-tcGenPragmas ty id ps = returnNF_Tc noIdInfo
-tcClassOpPragmas ty sel def spec ps = returnNF_Tc (noIdInfo, noIdInfo)
+Dictionary handling
+~~~~~~~~~~~~~~~~~~~
+Every class implicitly declares a new data type, corresponding to dictionaries
+of that class. So, for example:
-\end{code}
+ class (D a) => C a where
+ op1 :: a -> a
+ op2 :: forall b. Ord b => a -> b -> b
-\begin{code}
-tcClassDecl1 rec_inst_mapper
- (ClassDecl context class_name
- tyvar_name class_sigs def_methods pragmas src_loc)
- = tcAddSrcLoc src_loc $
- tcAddErrCtxt (classDeclCtxt class_name) $
+would implicitly declare
- -- LOOK THINGS UP IN THE ENVIRONMENT
- tcLookupClass class_name `thenNF_Tc` \ (class_kind, rec_class) ->
- tcLookupTyVar tyvar_name `thenNF_Tc` \ (tyvar_kind, rec_tyvar) ->
- let
- (rec_class_inst_env, rec_class_op_inst_fn) = rec_inst_mapper rec_class
- in
+ data CDict a = CDict (D a)
+ (a -> a)
+ (forall b. Ord b => a -> b -> b)
- -- FORCE THE CLASS AND ITS TYVAR TO HAVE SAME KIND
- unifyKind class_kind tyvar_kind `thenTc_`
+(We could use a record decl, but that means changing more of the existing apparatus.
+One step at at time!)
- -- CHECK THE CONTEXT
- tcClassContext rec_class rec_tyvar context pragmas
- `thenTc` \ (scs, sc_sel_ids) ->
+For classes with just one superclass+method, we use a newtype decl instead:
- -- CHECK THE CLASS SIGNATURES,
- mapTc (tcClassSig rec_class rec_tyvar rec_class_op_inst_fn) class_sigs
- `thenTc` \ sig_stuff ->
+ class C a where
+ op :: forallb. a -> b -> b
- -- MAKE THE CLASS OBJECT ITSELF
- tcGetUnique `thenNF_Tc` \ uniq ->
- let
- (ops, op_sel_ids, defm_ids) = unzip3 sig_stuff
- clas = mkClass uniq (getNameFullName class_name) rec_tyvar
- scs sc_sel_ids ops op_sel_ids defm_ids
- rec_class_inst_env
- in
- returnTc clas
-\end{code}
+generates
+ newtype CDict a = CDict (forall b. a -> b -> b)
-\begin{code}
-tcClassContext :: Class -> TyVar
- -> RenamedContext -- class context
- -> RenamedClassPragmas -- pragmas for superclasses
- -> TcM s ([Class], -- the superclasses
- [Id]) -- superclass selector Ids
+Now DictTy in Type is just a form of type synomym:
+ DictTy c t = TyConTy CDict `AppTy` t
-tcClassContext rec_class rec_tyvar context pragmas
- = -- Check the context.
- -- The renamer has already checked that the context mentions
- -- only the type variable of the class decl.
- tcContext context `thenTc` \ theta ->
- let
- super_classes = [ supers | (supers, _) <- theta ]
- in
+Death to "ExpandingDicts".
- -- Make super-class selector ids
- mapTc (mk_super_id rec_class)
- (super_classes `zip` maybe_pragmas) `thenTc` \ sc_sel_ids ->
- -- Done
- returnTc (super_classes, sc_sel_ids)
+%************************************************************************
+%* *
+\subsection{Type checking}
+%* *
+%************************************************************************
- where
- mk_super_id rec_class (super_class, maybe_pragma)
- = fixTc ( \ rec_super_id ->
- tcGetUnique `thenNF_Tc` \ uniq ->
-
- -- GET THE PRAGMA INFO FOR THE SUPERCLASS
- (case maybe_pragma of
- Nothing -> returnNF_Tc noIdInfo
- Just prag -> tcGenPragmas Nothing{-ty unknown-} rec_super_id prag
- ) `thenNF_Tc` \ id_info ->
- let
- ty = mkForAllTy rec_tyvar (
- mkFunTy (mkDictTy rec_class (mkTyVarTy rec_tyvar))
- (mkDictTy super_class (mkTyVarTy rec_tyvar))
- )
- in
- -- BUILD THE SUPERCLASS ID
- returnTc (mkSuperDictSelId uniq rec_class super_class ty id_info)
- )
-
- maybe_pragmas :: [Maybe RenamedGenPragmas]
- maybe_pragmas = case pragmas of
- NoClassPragmas -> repeat Nothing
- SuperDictPragmas prags -> ASSERT(length prags == length context)
- map Just prags
- -- If there are any pragmas there should
- -- be one for each superclass
-
-
-
-tcClassSig :: Class -- Knot tying only!
- -> TyVar -- The class type variable, used for error check only
- -> (ClassOp -> SpecEnv) -- Ditto; the spec info for the class ops
- -> RenamedClassOpSig
- -> TcM s (ClassOp, -- class op
- Id, -- selector id
- Id) -- default-method ids
-
-tcClassSig rec_clas rec_clas_tyvar rec_classop_spec_fn
- (ClassOpSig op_name
- (HsForAllTy tyvar_names context monotype)
- pragmas src_loc)
- = tcAddSrcLoc src_loc $
- fixTc ( \ ~(_, rec_sel_id, rec_defm_id) -> -- Knot for pragmas
+\begin{code}
- -- Check the type signature. NB that the envt *already has*
- -- bindings for the type variables; see comments in TcTyAndClassDcls.
- tcContext context `thenTc` \ theta ->
- tcMonoType monotype `thenTc` \ tau ->
- mapAndUnzipNF_Tc tcLookupTyVar tyvar_names `thenNF_Tc` \ (_,tyvars) ->
+tcClassDecl1 :: RecFlag -> RecTcEnv -> RenamedTyClDecl -> TcM (Name, TyThingDetails)
+tcClassDecl1 is_rec rec_env
+ (ClassDecl {tcdCtxt = context, tcdName = class_name,
+ tcdTyVars = tyvar_names, tcdFDs = fundeps,
+ tcdSigs = class_sigs, tcdMeths = def_methods,
+ tcdSysNames = sys_names, tcdLoc = src_loc})
+ = -- CHECK ARITY 1 FOR HASKELL 1.4
+ doptsTc Opt_GlasgowExts `thenTc` \ gla_ext_opt ->
+ let
+ gla_exts = gla_ext_opt || not (maybeToBool def_methods)
+ -- Accept extensions if gla_exts is on,
+ -- or if we're looking at an interface file decl
+ in -- (in which case def_methods = Nothing
+
+ checkTc (gla_exts || length tyvar_names == 1)
+ (classArityErr class_name) `thenTc_`
+
+ -- LOOK THINGS UP IN THE ENVIRONMENT
+ tcLookupClass class_name `thenTc` \ clas ->
let
- full_tyvars = rec_clas_tyvar : tyvars
- full_theta = (rec_clas, mkTyVarTy rec_clas_tyvar) : theta
- global_ty = mkSigmaTy full_tyvars full_theta tau
- local_ty = mkSigmaTy tyvars theta tau
- class_op = mkClassOp (getOccurrenceName op_name)
- (getTagFromClassOpName op_name)
- local_ty
+ tyvars = classTyVars clas
+ op_sigs = filter isClassOpSig class_sigs
+ op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
+ (_, datacon_name, datacon_wkr_name, sc_sel_names) = getClassDeclSysNames sys_names
in
+ tcExtendTyVarEnv tyvars $
+
+ -- SOURCE-CODE CONSISTENCY CHECKS
+ (case def_methods of
+ Nothing -> returnTc Nothing -- Not source
+ Just dms -> checkDefaultBinds clas op_names dms `thenTc` \ dm_env ->
+ checkGenericClassIsUnary clas dm_env `thenTc_`
+ returnTc (Just dm_env)
+ ) `thenTc` \ mb_dm_env ->
+
+ -- CHECK THE CONTEXT
+ tcSuperClasses is_rec gla_exts clas context sc_sel_names `thenTc` \ (sc_theta, sc_sel_ids) ->
- -- Munch the pragmas
- tcClassOpPragmas
- global_ty
- rec_sel_id rec_defm_id
- (rec_classop_spec_fn class_op)
- pragmas `thenNF_Tc` \ (op_info, defm_info) ->
+ -- CHECK THE CLASS SIGNATURES,
+ mapTc (tcClassSig is_rec rec_env clas tyvars mb_dm_env) op_sigs `thenTc` \ sig_stuff ->
- -- Build the selector id and default method id
- tcGetUnique `thenNF_Tc` \ d_uniq ->
+ -- MAKE THE CLASS DETAILS
let
- op_uniq = getItsUnique op_name
- sel_id = mkMethodSelId op_uniq rec_clas class_op global_ty op_info
- defm_id = mkDefaultMethodId d_uniq rec_clas class_op False global_ty defm_info
- -- ToDo: improve the "False"
+ (op_tys, op_items) = unzip sig_stuff
+ sc_tys = mkDictTys sc_theta
+ dict_component_tys = sc_tys ++ op_tys
+
+ dict_con = mkDataCon datacon_name
+ [notMarkedStrict | _ <- dict_component_tys]
+ [{- No labelled fields -}]
+ tyvars
+ [{-No context-}]
+ [{-No existential tyvars-}] [{-Or context-}]
+ dict_component_tys
+ (classTyCon clas)
+ dict_con_id dict_wrap_id
+
+ dict_con_id = mkDataConId datacon_wkr_name dict_con
+ dict_wrap_id = mkDataConWrapId dict_con
in
- returnTc (class_op, sel_id, defm_id)
- )
+ returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
\end{code}
+\begin{code}
+checkDefaultBinds :: Class -> [Name] -> RenamedMonoBinds
+ -> TcM (NameEnv Bool)
+ -- The returned environment says
+ -- x not in env => no default method
+ -- x -> True => generic default method
+ -- x -> False => polymorphic default method
-%************************************************************************
-%* *
-\subsection[ClassDcl-pass2]{Class decls pass 2: default methods}
-%* *
-%************************************************************************
+ -- Check default bindings
+ -- a) must be for a class op for this class
+ -- b) must be all generic or all non-generic
+ -- and return a mapping from class-op to DefMeth info
-The purpose of pass 2 is
-\begin{enumerate}
-\item
-to beat on the explicitly-provided default-method decls (if any),
-using them to produce a complete set of default-method decls.
-(Omitted ones elicit an error message.)
-\item
-to produce a definition for the selector function for each method
-and superclass dictionary.
-\end{enumerate}
+ -- But do all this only for source binds
-Pass~2 only applies to locally-defined class declarations.
+checkDefaultBinds clas ops EmptyMonoBinds = returnTc emptyNameEnv
-The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
-each local class decl.
+checkDefaultBinds clas ops (AndMonoBinds b1 b2)
+ = checkDefaultBinds clas ops b1 `thenTc` \ dm_info1 ->
+ checkDefaultBinds clas ops b2 `thenTc` \ dm_info2 ->
+ returnTc (dm_info1 `plusNameEnv` dm_info2)
-\begin{code}
-tcClassDecls2 :: Bag RenamedClassDecl
- -> NF_TcM s (LIE s, TcHsBinds s)
-
-tcClassDecls2 decls
- = foldBag combine
- tcClassDecl2
- (returnNF_Tc (emptyLIE, EmptyBinds))
- decls
+checkDefaultBinds clas ops (FunMonoBind op _ matches loc)
+ = tcAddSrcLoc loc $
+
+ -- Check that the op is from this class
+ checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
+
+ -- Check that all the defns ar generic, or none are
+ checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
+
+ returnTc (unitNameEnv op all_generic)
where
- combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
- tc2 `thenNF_Tc` \ (lie2, binds2) ->
- returnNF_Tc (lie1 `plusLIE` lie2,
- binds1 `ThenBinds` binds2)
+ n_generic = count (maybeToBool . maybeGenericMatch) matches
+ none_generic = n_generic == 0
+ all_generic = n_generic == length matches
+
+checkGenericClassIsUnary clas dm_env
+ = -- Check that if the class has generic methods, then the
+ -- class has only one parameter. We can't do generic
+ -- multi-parameter type classes!
+ checkTc (unary || no_generics) (genericMultiParamErr clas)
+ where
+ unary = length (classTyVars clas) == 1
+ no_generics = not (or (nameEnvElts dm_env))
\end{code}
-@tcClassDecl2@ is the business end of things.
\begin{code}
-tcClassDecl2 :: RenamedClassDecl -- The class declaration
- -> NF_TcM s (LIE s, TcHsBinds s)
-
-tcClassDecl2 (ClassDecl context class_name
- tyvar_name class_sigs default_binds pragmas src_loc)
+tcSuperClasses :: RecFlag -> Bool -> Class
+ -> RenamedContext -- class context
+ -> [Name] -- Names for superclass selectors
+ -> TcM (ClassContext, -- the superclass context
+ [Id]) -- superclass selector Ids
- | not (isLocallyDefined class_name)
- = returnNF_Tc (emptyLIE, EmptyBinds)
+tcSuperClasses is_rec gla_exts clas context sc_sel_names
+ = -- Check the context.
+ -- The renamer has already checked that the context mentions
+ -- only the type variable of the class decl.
- | otherwise -- It is locally defined
- = recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyBinds)) $
- tcAddSrcLoc src_loc $
+ -- For std Haskell check that the context constrains only tyvars
+ (if gla_exts then
+ returnTc ()
+ else
+ mapTc_ check_constraint context
+ ) `thenTc_`
- -- Get the relevant class
- tcLookupClass class_name `thenNF_Tc` \ (_, clas) ->
+ -- Context is already kind-checked
+ tcRecClassContext is_rec context `thenTc` \ sc_theta ->
let
- (tyvar, scs, sc_sel_ids, ops, op_sel_ids, defm_ids)
- = getClassBigSig clas
+ sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
in
- tcInstSigTyVars [tyvar] `thenNF_Tc` \ ([clas_tyvar], _, _) ->
-
- -- Generate bindings for the selector functions
- buildSelectors clas tyvar clas_tyvar scs sc_sel_ids ops op_sel_ids
- `thenNF_Tc` \ sel_binds ->
- -- Ditto for the methods
- buildDefaultMethodBinds clas clas_tyvar defm_ids default_binds
- `thenTc` \ (const_insts, meth_binds) ->
-
- returnTc (const_insts, sel_binds `ThenBinds` meth_binds)
-\end{code}
-
-%************************************************************************
-%* *
-\subsection[ClassDcl-bld-sels]{Building the selector functions for methods and superclasses}
-%* *
-%************************************************************************
+ -- Done
+ returnTc (sc_theta, sc_sel_ids)
-\begin{code}
-buildSelectors :: Class -- The class object
- -> TyVar -- Class type variable
- -> TcTyVar s -- Instantiated class type variable (TyVarTy)
- -> [Class] -> [Id] -- Superclasses and selectors
- -> [ClassOp] -> [Id] -- Class ops and selectors
- -> NF_TcM s (TcHsBinds s)
-
-buildSelectors clas clas_tyvar clas_tc_tyvar scs sc_sel_ids ops op_sel_ids
- =
- -- Make new Ids for the components of the dictionary
- let
- clas_tyvar_ty = mkTyVarTy clas_tc_tyvar
- mk_op_ty = tcInstType [(clas_tyvar, clas_tyvar_ty)] . getClassOpLocalType
- in
- mapNF_Tc mk_op_ty ops `thenNF_Tc` \ op_tys ->
- newLocalIds (map getClassOpString ops) op_tys `thenNF_Tc` \ method_ids ->
+ where
+ check_constraint sc@(HsPClass c tys)
+ = checkTc (all is_tyvar tys) (superClassErr clas sc)
- newDicts ClassDeclOrigin
- [ (super_clas, clas_tyvar_ty)
- | super_clas <- scs ] `thenNF_Tc` \ (_,dict_ids) ->
+ is_tyvar (HsTyVar _) = True
+ is_tyvar other = False
- newDicts ClassDeclOrigin
- [ (clas, clas_tyvar_ty) ] `thenNF_Tc` \ (_,[clas_dict]) ->
- -- Make suitable bindings for the selectors
- let
- mk_sel sel_id method_or_dict
- = mkSelBind sel_id clas_tc_tyvar clas_dict dict_ids method_ids method_or_dict
- in
- listNF_Tc (zipWithEqual mk_sel op_sel_ids method_ids) `thenNF_Tc` \ op_sel_binds ->
- listNF_Tc (zipWithEqual mk_sel sc_sel_ids dict_ids) `thenNF_Tc` \ sc_sel_binds ->
-
- returnNF_Tc (SingleBind (
- NonRecBind (
- foldr AndMonoBinds
- (foldr AndMonoBinds EmptyMonoBinds op_sel_binds)
- sc_sel_binds
- )))
-\end{code}
+tcClassSig :: RecFlag -> RecTcEnv -- Knot tying only!
+ -> Class -- ...ditto...
+ -> [TyVar] -- The class type variable, used for error check only
+ -> Maybe (NameEnv Bool) -- Info about default methods
+ -> RenamedClassOpSig
+ -> TcM (Type, -- Type of the method
+ ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
-%************************************************************************
-%* *
-\subsection[ClassDcl-misc]{Miscellaneous}
-%* *
-%************************************************************************
+-- This warrants an explanation: we need to separate generic
+-- default methods and default methods later on in the compiler
+-- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
+-- Class.DefMeth data structure.
-Make a selector expression for @sel_id@ from a dictionary @clas_dict@
-consisting of @dicts@ and @methods@.
+tcClassSig is_rec unf_env clas clas_tyvars maybe_dm_env
+ (ClassOpSig op_name sig_dm op_ty src_loc)
+ = tcAddSrcLoc src_loc $
-We have to do a bit of jiggery pokery to get the type variables right.
-Suppose we have the class decl:
-\begin{verbatim}
- class Foo a where
- op1 :: Ord b => a -> b -> a
- op2 :: ...
-\end{verbatim}
-Then the method selector for \tr{op1} is like this:
-\begin{verbatim}
- op1_sel = /\a b -> \dFoo dOrd -> case dFoo of
- (op1_method,op2_method) -> op1_method b dOrd
-\end{verbatim}
-Note that the type variable for \tr{b} and the (Ord b) dictionary
-are lifted to the top lambda, and
-\tr{op1_method} is applied to them. This is preferable to the alternative:
-\begin{verbatim}
- op1_sel' = /\a -> \dFoo -> case dFoo of
- (op1_method,op2_method) -> op1_method
-\end{verbatim}
-because \tr{op1_sel'} then has the rather strange type
-\begin{verbatim}
- op1_sel' :: forall a. Foo a -> forall b. Ord b -> a -> b -> a
-\end{verbatim}
-whereas \tr{op1_sel} (the one we use) has the decent type
-\begin{verbatim}
- op1_sel :: forall a b. Foo a -> Ord b -> a -> b -> a
-\end{verbatim}
+ -- Check the type signature. NB that the envt *already has*
+ -- bindings for the type variables; see comments in TcTyAndClassDcls.
-NOTE that we return a TcMonoBinds (which is later zonked) even though
-there's no real back-substitution to do. It's just simpler this way!
+ tcHsRecType is_rec op_ty `thenTc` \ local_ty ->
-NOTE ALSO that the selector has no free type variables, so we
-don't bother to instantiate the class-op's local type; instead
-we just use the variables inside it.
+ -- Check for ambiguous class op types
+ let
+ theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
+ in
+ checkAmbiguity is_rec True clas_tyvars theta local_ty `thenTc` \ global_ty ->
+ -- The default method's type should really come from the
+ -- iface file, since it could be usage-generalised, but this
+ -- requires altering the mess of knots in TcModule and I'm
+ -- too scared to do that. Instead, I have disabled generalisation
+ -- of types of default methods (and dict funs) by annotating them
+ -- TyGenNever (in MkId). Ugh! KSW 1999-09.
-\begin{code}
-mkSelBind :: Id -- the selector id
- -> TcTyVar s -> TcIdOcc s -- class tyvar and dict
- -> [TcIdOcc s] -> [TcIdOcc s] -- superclasses and methods in class dict
- -> TcIdOcc s -- the superclass/method being slected
- -> NF_TcM s (TcMonoBinds s)
-
-mkSelBind sel_id clas_tyvar clas_dict dicts methods method_or_dict@(TcId op)
- = let
- (op_tyvars,op_theta,op_tau) = splitSigmaTy (idType op)
- op_tys = mkTyVarTys op_tyvars
+ let
+ -- Build the selector id and default method id
+ sel_id = mkDictSelId op_name clas
+ dm_id = mkDefaultMethodId dm_name clas global_ty
+ DefMeth dm_name = sig_dm
+
+ dm_info = case maybe_dm_env of
+ Nothing -> iface_dm_info
+ Just dm_env -> mk_src_dm_info dm_env
+
+ iface_dm_info = case sig_dm of
+ NoDefMeth -> NoDefMeth
+ GenDefMeth -> GenDefMeth
+ DefMeth dm_name -> DefMeth (tcAddImportedIdInfo unf_env dm_id)
+
+ mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
+ Nothing -> NoDefMeth
+ Just True -> GenDefMeth
+ Just False -> DefMeth dm_id
in
- newDicts ClassDeclOrigin op_theta `thenNF_Tc` \ (_, op_dicts) ->
-
- -- sel_id = /\ clas_tyvar op_tyvars -> \ clas_dict op_dicts ->
- -- case clas_dict of
- -- <dicts..methods> -> method_or_dict op_tyvars op_dicts
-
- returnNF_Tc (VarMonoBind (RealId sel_id) (
- TyLam (clas_tyvar:op_tyvars) (
- DictLam (clas_dict:op_dicts) (
- HsCase
- (HsVar clas_dict)
- ([PatMatch (DictPat dicts methods) (
- GRHSMatch (GRHSsAndBindsOut
- [OtherwiseGRHS
- (mkHsDictApp (mkHsTyApp (HsVar method_or_dict) op_tys) op_dicts)
- mkGeneratedSrcLoc]
- EmptyBinds
- op_tau))])
- mkGeneratedSrcLoc
- ))))
+ -- Check that for a generic method, the type of
+ -- the method is sufficiently simple
+ checkTc (dm_info /= GenDefMeth || validGenericMethodType local_ty)
+ (badGenericMethodType op_name op_ty) `thenTc_`
+
+ returnTc (local_ty, (sel_id, dm_info))
\end{code}
defm.Foo.op1 :: forall a. Foo a => a -> Bool
defm.Foo.op1 = /\a -> \dfoo -> \x -> True
-defm.Foo.op2 :: forall a, b. (Foo a, Ord b) => a -> b -> b -> b
-defm.Foo.op2 = /\ a b -> \ dfoo dord -> \x y z ->
+defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
+defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
if (op1 a dfoo x) && (< b dord y z) then y else z
\end{verbatim}
-Notice that, like all ids, the foralls of defm.Foo.op2 are at the top.
When we come across an instance decl, we may need to use the default
methods:
const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
-const.Foo.Int.op2 = /\b -> defm.Foo.op2 Int b dfun.Foo.Int
+const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
dfun.Foo.Int :: Foo Int
dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
\end{verbatim}
Notice that, as with method selectors above, we assume that dictionary
application is curried, so there's no need to mention the Ord dictionary
-in const.Foo.Int.op2
+in const.Foo.Int.op2 (or the type variable).
+
\begin{verbatim}
instance Foo a => Foo [a] where {}
= /\ a -> \ dfoo_a ->
let rec
op1 = defm.Foo.op1 [a] dfoo_list
- op2 = /\b -> \dord -> defm.Foo.op2 [a] b dfoo_list dord
+ op2 = defm.Foo.op2 [a] dfoo_list
dfoo_list = (op1, op2)
in
dfoo_list
\end{verbatim}
+The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
+each local class decl.
+
\begin{code}
-buildDefaultMethodBinds
- :: Class
- -> TcTyVar s
- -> [Id]
- -> RenamedMonoBinds
- -> TcM s (LIE s, TcHsBinds s)
-
-buildDefaultMethodBinds clas clas_tyvar
- default_method_ids default_binds
- = -- Deal with the method declarations themselves
- mapNF_Tc unZonkId default_method_ids `thenNF_Tc` \ tc_defm_ids ->
- processInstBinds
- (makeClassDeclDefaultMethodRhs clas default_method_ids)
- [] -- No tyvars in scope for "this inst decl"
- emptyLIE -- No insts available
- (map TcId tc_defm_ids)
- default_binds `thenTc` \ (dicts_needed, default_binds') ->
-
- returnTc (dicts_needed, SingleBind (NonRecBind default_binds'))
+tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds)
+
+tcClassDecls2 this_mod decls
+ = foldr combine
+ (returnNF_Tc (emptyLIE, EmptyMonoBinds))
+ [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
+ -- The 'Just' picks out source ClassDecls
+ where
+ combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
+ tc2 `thenNF_Tc` \ (lie2, binds2) ->
+ returnNF_Tc (lie1 `plusLIE` lie2,
+ binds1 `AndMonoBinds` binds2)
\end{code}
-@makeClassDeclDefaultMethodRhs@ builds the default method for a
-class declaration when no explicit default method is given.
+@tcClassDecl2@ generates bindings for polymorphic default methods
+(generic default methods have by now turned into instance declarations)
\begin{code}
-makeClassDeclDefaultMethodRhs
- :: Class
- -> [Id]
- -> Int
- -> NF_TcM s (TcExpr s)
-
-makeClassDeclDefaultMethodRhs clas method_ids tag
- = tcInstType [] (idType method_id) `thenNF_Tc` \ method_ty ->
- let
- (tyvars, theta, tau) = splitSigmaTy method_ty
- in
- newDicts ClassDeclOrigin theta `thenNF_Tc` \ (lie, dict_ids) ->
-
- returnNF_Tc (mkHsTyLam tyvars (
- mkHsDictLam dict_ids (
- HsApp (mkHsTyApp (HsVar (RealId pAT_ERROR_ID)) [tau])
- (HsLitOut (HsString (_PK_ error_msg)) stringTy))))
+tcClassDecl2 :: RenamedTyClDecl -- The class declaration
+ -> NF_TcM (LIE, TcMonoBinds)
+
+tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
+ tcdMeths = Just default_binds, tcdLoc = src_loc})
+ = -- The 'Just' picks out source ClassDecls
+ recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
+ tcAddSrcLoc src_loc $
+ tcLookupClass class_name `thenNF_Tc` \ clas ->
+
+ -- We make a separate binding for each default method.
+ -- At one time I used a single AbsBinds for all of them, thus
+ -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
+ -- But that desugars into
+ -- ds = \d -> (..., ..., ...)
+ -- dm1 = \d -> case ds d of (a,b,c) -> a
+ -- And since ds is big, it doesn't get inlined, so we don't get good
+ -- default methods. Better to make separate AbsBinds for each
+ let
+ (tyvars, _, _, op_items) = classBigSig clas
+ prags = filter isPragSig sigs
+ tc_dm = tcDefMeth clas tyvars default_binds prags
+ in
+ mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
+
+ returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
+
+
+tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
+tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
+ -- Generate code for polymorphic default methods only
+ -- (Generic default methods have turned into instance decls by now.)
+ -- This is incompatible with Hugs, which expects a polymorphic
+ -- default method for every class op, regardless of whether or not
+ -- the programmer supplied an explicit default decl for the class.
+ -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
+
+tcDefMeth clas tyvars binds_in prags op_item@(_, DefMeth dm_id)
+ = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
+ let
+ theta = [(mkClassPred clas inst_tys)]
+ in
+ newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
+
+ tcExtendTyVarEnvForMeths tyvars clas_tyvars (
+ tcMethodBind clas origin clas_tyvars inst_tys theta
+ binds_in prags False op_item
+ ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
+
+ tcAddErrCtxt (defltMethCtxt clas) $
+
+ -- tcMethodBind has checked that the class_tyvars havn't
+ -- been unified with each other or another type, but we must
+ -- still zonk them before passing them to tcSimplifyAndCheck
+ zonkTcSigTyVars clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
+
+ -- Check the context
+ tcSimplifyAndCheck
+ (ptext SLIT("class") <+> ppr clas)
+ (mkVarSet clas_tyvars')
+ this_dict
+ insts_needed `thenTc` \ (const_lie, dict_binds) ->
+
+ let
+ full_bind = AbsBinds
+ clas_tyvars'
+ [this_dict_id]
+ [(clas_tyvars', dm_id, local_dm_id)]
+ emptyNameSet -- No inlines (yet)
+ (dict_binds `andMonoBinds` defm_bind)
+ in
+ returnTc (full_bind, const_lie)
where
- (clas_mod, clas_name) = getOrigName clas
+ origin = ClassDeclOrigin
+\end{code}
- method_id = method_ids !! (tag-1)
- class_op = (getClassOps clas) !! (tag-1)
+
- error_msg = "%D" -- => No default method for \"
- ++ unencoded_part_of_msg
+%************************************************************************
+%* *
+\subsection{Typechecking a method}
+%* *
+%************************************************************************
+
+@tcMethodBind@ is used to type-check both default-method and
+instance-decl method declarations. We must type-check methods one at a
+time, because their signatures may have different contexts and
+tyvar sets.
- unencoded_part_of_msg = escErrorMsg (
- _UNPK_ clas_mod ++ "." ++ _UNPK_ clas_name ++ "."
- ++ (ppShow 80 (ppr PprForUser class_op))
- ++ "\"" )
+\begin{code}
+tcMethodBind
+ :: Class
+ -> InstOrigin
+ -> [TcTyVar] -- Instantiated type variables for the
+ -- enclosing class/instance decl.
+ -- They'll be signature tyvars, and we
+ -- want to check that they don't get bound
+ -> [TcType] -- Instance types
+ -> TcThetaType -- Available theta; this could be used to check
+ -- the method signature, but actually that's done by
+ -- the caller; here, it's just used for the error message
+ -> RenamedMonoBinds -- Method binding (pick the right one from in here)
+ -> [RenamedSig] -- Pramgas (just for this one)
+ -> Bool -- True <=> This method is from an instance declaration
+ -> ClassOpItem -- The method selector and default-method Id
+ -> TcM (TcMonoBinds, LIE, (LIE, TcId))
+
+tcMethodBind clas origin inst_tyvars inst_tys inst_theta
+ meth_binds prags is_inst_decl (sel_id, dm_info)
+ = tcGetSrcLoc `thenNF_Tc` \ loc ->
+ newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
+ mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
+ let
+ meth_name = idName meth_id
+ sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_id
+ meth_prags = find_prags (idName sel_id) meth_name prags
+ in
+ -- Figure out what method binding to use
+ -- If the user suppplied one, use it, else construct a default one
+ (case find_bind (idName sel_id) meth_name meth_binds of
+ Just user_bind -> returnTc user_bind
+ Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
+ returnTc (FunMonoBind meth_name False -- Not infix decl
+ [mkSimpleMatch [] rhs Nothing loc] loc)
+ ) `thenTc` \ meth_bind ->
+ -- Check the bindings; first add inst_tyvars to the envt
+ -- so that we don't quantify over them in nested places
+ -- The *caller* put the class/inst decl tyvars into the envt
+ tcExtendGlobalTyVars (mkVarSet inst_tyvars)
+ (tcAddErrCtxt (methodCtxt sel_id) $
+ tcBindWithSigs NotTopLevel meth_bind
+ [sig_info] meth_prags NonRecursive
+ ) `thenTc` \ (binds, insts, _) ->
+
+ tcExtendLocalValEnv [(meth_name, meth_id)]
+ (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
+
+ -- The prag_lie for a SPECIALISE pragma will mention the function
+ -- itself, so we have to simplify them away right now lest they float
+ -- outwards!
+ bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
+
+ -- Now check that the instance type variables
+ -- (or, in the case of a class decl, the class tyvars)
+ -- have not been unified with anything in the environment
+ --
+ -- We do this for each method independently to localise error messages
+ -- ...and this is why the call to tcExtendGlobalTyVars must be here
+ -- rather than in the caller
+ tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
+ checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
+
+ returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
+ insts `plusLIE` prag_lie',
+ meth)
+
+ -- The user didn't supply a method binding,
+ -- so we have to make up a default binding
+ -- The RHS of a default method depends on the default-method info
+mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
+ = -- An polymorphic default method
+ returnTc (HsVar (idName dm_id))
+
+mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
+ = -- No default method
+ -- Warn only if -fwarn-missing-methods
+ doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
+ warnTc (is_inst_decl && warn)
+ (omittedMethodWarn sel_id clas) `thenNF_Tc_`
+ returnTc error_rhs
+ where
+ error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
+ (HsLit (HsString (_PK_ error_msg)))
+ error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
+
+
+mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
+ = -- A generic default method
+ -- If the method is defined generically, we can only do the job if the
+ -- instance declaration is for a single-parameter type class with
+ -- a type constructor applied to type arguments in the instance decl
+ -- (checkTc, so False provokes the error)
+ checkTc (not is_inst_decl || simple_inst)
+ (badGenericInstance sel_id clas) `thenTc_`
+
+ ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
+ returnTc rhs
+ where
+ rhs = mkGenericRhs sel_id clas_tyvar tycon
+
+ stuff = vcat [ppr clas <+> ppr inst_tys,
+ nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
+
+ -- The tycon is only used in the generic case, and in that
+ -- case we require that the instance decl is for a single-parameter
+ -- type class with type variable arguments:
+ -- instance (...) => C (T a b)
+ simple_inst = maybeToBool maybe_tycon
+ clas_tyvar = head (classTyVars clas)
+ Just tycon = maybe_tycon
+ maybe_tycon = case inst_tys of
+ [ty] -> case splitTyConApp_maybe ty of
+ Just (tycon, arg_tys) | all isTyVarTy arg_tys -> Just tycon
+ other -> Nothing
+ other -> Nothing
\end{code}
-Contexts
-~~~~~~~~
\begin{code}
-classDeclCtxt class_name sty
- = ppCat [ppStr "In the class declaration for", ppr sty class_name]
+-- The renamer just puts the selector ID as the binder in the method binding
+-- but we must use the method name; so we substitute it here. Crude but simple.
+find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
+ | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
+find_bind sel_name meth_name (AndMonoBinds b1 b2)
+ = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
+find_bind sel_name meth_name other = Nothing -- Default case
+
+ -- Find the prags for this method, and replace the
+ -- selector name with the method name
+find_prags sel_name meth_name [] = []
+find_prags sel_name meth_name (SpecSig name ty loc : prags)
+ | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
+find_prags sel_name meth_name (InlineSig name phase loc : prags)
+ | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
+find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
+ | name == sel_name = NoInlineSig meth_name phase loc : find_prags sel_name meth_name prags
+find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
+\end{code}
+
+
+Contexts and errors
+~~~~~~~~~~~~~~~~~~~
+\begin{code}
+classArityErr class_name
+ = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
+
+superClassErr clas sc
+ = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
+ <+> ptext SLIT("in declaration for class") <+> quotes (ppr clas)
+
+defltMethCtxt clas
+ = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
+
+methodCtxt sel_id
+ = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
+
+badMethodErr clas op
+ = hsep [ptext SLIT("Class"), quotes (ppr clas),
+ ptext SLIT("does not have a method"), quotes (ppr op)]
+
+omittedMethodWarn sel_id clas
+ = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
+ ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
+
+badGenericMethodType op op_ty
+ = hang (ptext SLIT("Generic method type is too complex"))
+ 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
+ ptext SLIT("You can only use type variables, arrows, and tuples")])
+
+badGenericInstance sel_id clas
+ = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
+ ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
+ ptext SLIT("(where T is a derivable type constructor)"),
+ ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
+
+mixedGenericErr op
+ = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
+
+genericMultiParamErr clas
+ = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
+ ptext SLIT("cannot have generic methods")
\end{code}