import CmdLineOpts ( DynFlag(..) )
import TcRnMonad
-import TcEnv ( tcGetInstEnv, tcSetInstEnv, newDFunName, InstInfo(..), pprInstInfo,
+import TcEnv ( tcGetInstEnv, tcSetInstEnv, newDFunName,
+ InstInfo(..), pprInstInfo, InstBindings(..),
pprInstInfoDetails, tcLookupTyCon, tcExtendTyVarEnv
)
import TcGenDeriv -- Deriv stuff
import HscTypes ( DFunId )
import BasicTypes ( NewOrData(..) )
-import Class ( className, classKey, classTyVars, Class )
+import Class ( className, classArity, classKey, classTyVars, classSCTheta, Class )
+import Subst ( mkTyVarSubst, substTheta )
import ErrUtils ( dumpIfSet_dyn )
import MkId ( mkDictFunId )
-import DataCon ( dataConRepArgTys, isNullaryDataCon, isExistentialDataCon )
+import DataCon ( dataConRepArgTys, dataConOrigArgTys, isNullaryDataCon, isExistentialDataCon )
import Maybes ( maybeToBool, catMaybes )
import Name ( Name, getSrcLoc, nameUnique )
import NameSet
import RdrName ( RdrName )
-import TyCon ( tyConTyVars, tyConDataCons, tyConArity, newTyConRep,
+import TyCon ( tyConTyVars, tyConDataCons, tyConArity,
tyConTheta, maybeTyConSingleCon, isDataTyCon,
isEnumerationTyCon, isRecursiveTyCon, TyCon
)
import TcType ( TcType, ThetaType, mkTyVarTys, mkTyConApp, getClassPredTys_maybe,
isUnLiftedType, mkClassPred, tyVarsOfTypes, tcSplitFunTys,
- tcSplitTyConApp_maybe, tcEqTypes )
+ tcEqTypes, tcSplitAppTys, mkAppTys )
import Var ( TyVar, tyVarKind )
import VarSet ( mkVarSet, subVarSet )
import PrelNames
import Util ( zipWithEqual, sortLt, notNull )
import ListSetOps ( removeDups, assoc )
import Outputable
-import Maybe ( isJust )
\end{code}
%************************************************************************
\end{code}
-A note about contexts on data decls
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+[Data decl contexts] A note about contexts on data decls
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
-- Make a Real dfun instead of the dummy one we have so far
gen_inst_info :: DFunId -> RenamedMonoBinds -> InstInfo
gen_inst_info dfun binds
- = InstInfo { iDFunId = dfun, iBinds = binds, iPrags = [] }
+ = InstInfo { iDFunId = dfun, iBinds = VanillaInst binds [] }
rn_meths (cls, meths) = rnMethodBinds cls [] meths
\end{code}
constraints = extra_constraints ++
[ mkClassPred clas [arg_ty]
| data_con <- tyConDataCons tycon,
- arg_ty <- dataConRepArgTys data_con,
+ arg_ty <- dataConRepArgTys data_con, -- dataConOrigArgTys???
-- Use the same type variables
-- as the type constructor,
-- hence no need to instantiate
not (isUnLiftedType arg_ty) -- No constraints for unlifted types?
]
- -- "extra_constraints": see notes above about contexts on data decls
+ -- "extra_constraints": see note [Data decl contexts] above
extra_constraints = tyConTheta tycon
- -- | offensive_class = tyConTheta tycon
- -- | otherwise = []
- -- offensive_class = classKey clas `elem` PrelInfo.needsDataDeclCtxtClassKeys
-
-
mk_eqn_help NewType tycon clas tys
= doptM Opt_GlasgowExts `thenM` \ gla_exts ->
if can_derive_via_isomorphism && (gla_exts || standard_instance) then
-- Go ahead and use the isomorphism
+ traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys) `thenM_`
new_dfun_name clas tycon `thenM` \ dfun_name ->
- returnM (Nothing, Just (NewTypeDerived (mk_dfun dfun_name)))
+ returnM (Nothing, Just (InstInfo { iDFunId = mk_dfun dfun_name,
+ iBinds = NewTypeDerived rep_tys }))
else
if standard_instance then
mk_eqn_help DataType tycon clas [] -- Go via bale-out route
bale_out cant_derive_err
where
-- Here is the plan for newtype derivings. We see
- -- newtype T a1...an = T (t ak...an) deriving (C1...Cm)
- -- where aj...an do not occur free in t, and the Ci are *partial applications* of
- -- classes with the last parameter missing
+ -- newtype T a1...an = T (t ak...an) deriving (.., C s1 .. sm, ...)
+ -- where aj...an do not occur free in t, and the (C s1 ... sm) is a
+ -- *partial applications* of class C with the last parameter missing
--
-- We generate the instances
- -- instance Ci (t ak...aj) => Ci (T a1...aj)
+ -- instance C s1 .. sm (t ak...aj) => C s1 .. sm (T a1...aj)
-- where T a1...aj is the partial application of the LHS of the correct kind
--
-- Running example: newtype T s a = MkT (ST s a) deriving( Monad )
+ -- instance Monad (ST s) => Monad (T s) where
+ -- fail = coerce ... (fail @ ST s)
- kind = tyVarKind (last (classTyVars clas))
+ clas_tyvars = classTyVars clas
+ kind = tyVarKind (last clas_tyvars)
-- Kind of the thing we want to instance
-- e.g. argument kind of Monad, *->*
-- Want to drop 1 arg from (T s a) and (ST s a)
-- to get instance Monad (ST s) => Monad (T s)
- (tyvars, rep_ty) = newTyConRep tycon
- maybe_rep_app = tcSplitTyConApp_maybe rep_ty
- Just (rep_tc, rep_ty_args) = maybe_rep_app
+ -- Note [newtype representation]
+ -- We must not use newTyConRep to get the representation
+ -- type, because that looks through all intermediate newtypes
+ -- To get the RHS of *this* newtype, just look at the data
+ -- constructor. For example
+ -- newtype B = MkB Int
+ -- newtype A = MkA B deriving( Num )
+ -- We want the Num instance of B, *not* the Num instance of Int,
+ -- when making the Num instance of A!
+ tyvars = tyConTyVars tycon
+ rep_ty = head (dataConOrigArgTys (head (tyConDataCons tycon)))
+ (rep_fn, rep_ty_args) = tcSplitAppTys rep_ty
n_tyvars_to_keep = tyConArity tycon - n_args_to_drop
tyvars_to_drop = drop n_tyvars_to_keep tyvars
tyvars_to_keep = take n_tyvars_to_keep tyvars
- n_args_to_keep = tyConArity rep_tc - n_args_to_drop
+ n_args_to_keep = length rep_ty_args - n_args_to_drop
args_to_drop = drop n_args_to_keep rep_ty_args
args_to_keep = take n_args_to_keep rep_ty_args
- ctxt_pred = mkClassPred clas (tys ++ [mkTyConApp rep_tc args_to_keep])
+ rep_tys = tys ++ [mkAppTys rep_fn args_to_keep]
+ rep_pred = mkClassPred clas rep_tys
+ -- rep_pred is the representation dictionary, from where
+ -- we are gong to get all the methods for the newtype dictionary
+
+ inst_tys = (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)])
+ -- The 'tys' here come from the partial application
+ -- in the deriving clause. The last arg is the new
+ -- instance type.
+
+ -- We must pass the superclasses; the newtype might be an instance
+ -- of them in a different way than the representation type
+ -- E.g. newtype Foo a = Foo a deriving( Show, Num, Eq )
+ -- Then the Show instance is not done via isomprphism; it shows
+ -- Foo 3 as "Foo 3"
+ -- The Num instance is derived via isomorphism, but the Show superclass
+ -- dictionary must the Show instance for Foo, *not* the Show dictionary
+ -- gotten from the Num dictionary. So we must build a whole new dictionary
+ -- not just use the Num one. The instance we want is something like:
+ -- instance (Num a, Show (Foo a), Eq (Foo a)) => Num (Foo a) where
+ -- (+) = ((+)@a)
+ -- ...etc...
+ -- There's no 'corece' needed because after the type checker newtypes
+ -- are transparent.
+
+ sc_theta = substTheta (mkTyVarSubst clas_tyvars inst_tys)
+ (classSCTheta clas)
+
+ -- If there are no tyvars, there's no need
+ -- to abstract over the dictionaries we need
+ dict_args | null tyvars = []
+ | otherwise = rep_pred : sc_theta
+
+ -- Finally! Here's where we build the dictionary Id
+ mk_dfun dfun_name = mkDictFunId dfun_name tyvars dict_args clas inst_tys
+
+ -------------------------------------------------------------------
+ -- Figuring out whether we can only do this newtype-deriving thing
- mk_dfun dfun_name = mkDictFunId dfun_name clas tyvars
- (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)] )
- [ctxt_pred]
-
- -- We can only do this newtype deriving thing if:
standard_instance = null tys && classKey clas `elem` derivableClassKeys
can_derive_via_isomorphism
= not (clas `hasKey` readClassKey) -- Never derive Read,Show this way
&& not (clas `hasKey` showClassKey)
+ && length tys + 1 == classArity clas -- Well kinded;
+ -- eg not: newtype T ... deriving( ST )
+ -- because ST needs *2* type params
&& n_tyvars_to_keep >= 0 -- Well kinded;
-- eg not: newtype T = T Int deriving( Monad )
- && isJust maybe_rep_app -- The rep type is a type constructor app
&& n_args_to_keep >= 0 -- Well kinded:
-- eg not: newtype T a = T Int deriving( Monad )
&& eta_ok -- Eta reduction works
&& (tyVarsOfTypes args_to_keep `subVarSet` mkVarSet tyvars_to_keep)
cant_derive_err = derivingThingErr clas tys tycon tyvars_to_keep
- (ptext SLIT("too hard for cunning newtype deriving"))
+ (vcat [ptext SLIT("too hard for cunning newtype deriving"),
+ ptext SLIT("debug info:") <+> ppr n_tyvars_to_keep <+>
+ ppr n_args_to_keep <+> ppr eta_ok <+>
+ ppr (isRecursiveTyCon tycon)
+ ])
bale_out err = addErrTc err `thenM_` returnM (Nothing, Nothing)
------------------------------------------------------------------
chk_out :: Class -> TyCon -> [TcType] -> Maybe SDoc
chk_out clas tycon tys
- | notNull tys = Just non_std_why
+ | notNull tys = Just ty_args_why
| not (getUnique clas `elem` derivableClassKeys) = Just non_std_why
| clas `hasKey` enumClassKey && not is_enumeration = Just nullary_why
| clas `hasKey` boundedClassKey && not is_enumeration_or_single = Just single_nullary_why
is_single_con = maybeToBool (maybeTyConSingleCon tycon)
is_enumeration_or_single = is_enumeration || is_single_con
- single_nullary_why = ptext SLIT("one constructor data type or type with all nullary constructors expected")
- nullary_why = ptext SLIT("data type with all nullary constructors expected")
- no_cons_why = ptext SLIT("type has no data constructors")
- non_std_why = ptext SLIT("not a derivable class")
- existential_why = ptext SLIT("it has existentially-quantified constructor(s)")
+ single_nullary_why = ptext SLIT("one constructor data type or type with all nullary constructors expected")
+ nullary_why = quotes (ppr tycon) <+> ptext SLIT("has non-nullary constructors")
+ no_cons_why = quotes (ppr tycon) <+> ptext SLIT("has no data constructors")
+ ty_args_why = quotes (ppr pred) <+> ptext SLIT("is not a class")
+ non_std_why = quotes (ppr clas) <+> ptext SLIT("is not a derivable class")
+ existential_why = quotes (ppr tycon) <+> ptext SLIT("has existentially-quantified constructor(s)")
+
+ pred = mkClassPred clas tys
new_dfun_name clas tycon -- Just a simple wrapper
= newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
-- They'll appear later, when we do the top-level extendInstEnvs
mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
- = mkDictFunId dfun_name clas tyvars
- [mkTyConApp tycon (mkTyVarTys tyvars)]
- theta
+ = mkDictFunId dfun_name tyvars theta
+ clas [mkTyConApp tycon (mkTyVarTys tyvars)]
\end{code}
%************************************************************************