import ListSetOps
import Outputable
import Bag
+
+import Monad (unless)
\end{code}
%************************************************************************
-- The "deriv_pred" is a LHsType to take account of the fact that for
-- newtype deriving we allow deriving (forall a. C [a]).
; mkEqnHelp DerivOrigin (tvs++deriv_tvs) cls cls_tys tc_app } }
+deriveTyData (deriv_pred, other_decl)
+ = panic "derivTyData" -- Caller ensures that only TyData can happen
------------------------------------------------------------------
mkEqnHelp orig tvs cls cls_tys tc_app
full_tc_args = tc_args ++ mkTyVarTys extra_tvs
full_tvs = tvs ++ extra_tvs
- ; (rep_tc, rep_tc_args) <- tcLookupFamInst tycon full_tc_args
+ ; (rep_tc, rep_tc_args) <- tcLookupFamInstExact tycon full_tc_args
; gla_exts <- doptM Opt_GlasgowExts
; overlap_flag <- getOverlapFlag
- ; if isDataTyCon tycon then
+
+ -- Be careful to test rep_tc here: in the case of families, we want
+ -- to check the instance tycon, not the family tycon
+ ; if isDataTyCon rep_tc then
mkDataTypeEqn orig gla_exts full_tvs cls cls_tys
tycon full_tc_args rep_tc rep_tc_args
else
baleOut err = addErrTc err >> returnM (Nothing, Nothing)
\end{code}
+Auxiliary lookup wrapper which requires that looked up family instances are
+not type instances.
+
+\begin{code}
+tcLookupFamInstExact :: TyCon -> [Type] -> TcM (TyCon, [Type])
+tcLookupFamInstExact tycon tys
+ = do { result@(rep_tycon, rep_tys) <- tcLookupFamInst tycon tys
+ ; let { tvs = map (Type.getTyVar
+ "TcDeriv.tcLookupFamInstExact")
+ tys
+ ; variable_only_subst = all Type.isTyVarTy rep_tys &&
+ sizeVarSet (mkVarSet tvs) == length tvs
+ -- renaming may have no repetitions
+ }
+ ; unless variable_only_subst $
+ famInstNotFound tycon tys [result]
+ ; return result
+ }
+
+\end{code}
+
%************************************************************************
%* *
| isProductTyCon rep_tc = Nothing
| otherwise = Just why
where
- why = (pprSourceTyCon rep_tc) <+>
+ why = quotes (pprSourceTyCon rep_tc) <+>
ptext SLIT("has more than one constructor")
cond_typeableOK :: Condition
where
why = ptext SLIT("You need -fglasgow-exts to derive an instance for this class")
-std_class gla_exts clas
- = key `elem` derivableClassKeys
- || (gla_exts && (key == typeableClassKey || key == dataClassKey))
- where
- key = classKey clas
-
std_class_via_iso clas -- These standard classes can be derived for a newtype
-- using the isomorphism trick *even if no -fglasgow-exts*
= classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey]
new_dfun_name clas tycon -- Just a simple wrapper
- = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
+ = newDFunName clas [mkTyConApp tycon []] (getSrcSpan tycon)
-- The type passed to newDFunName is only used to generate
-- a suitable string; hence the empty type arg list
\end{code}
tycon tc_args
rep_tycon rep_tc_args
| can_derive_via_isomorphism && (gla_exts || std_class_via_iso cls)
- = do { traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys)
- ; -- Go ahead and use the isomorphism
- dfun_name <- new_dfun_name cls tycon
- ; return (Nothing, Just (InstInfo { iSpec = mk_inst_spec dfun_name,
- iBinds = NewTypeDerived ntd_info })) }
- | std_class gla_exts cls
- = mkDataTypeEqn orig gla_exts tvs cls cls_tys tycon tc_args rep_tycon rep_tc_args -- Go via bale-out route
-
- -- Otherwise its a non-standard instance
+ = do { traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys)
+ ; -- Go ahead and use the isomorphism
+ dfun_name <- new_dfun_name cls tycon
+ ; return (Nothing, Just (InstInfo { iSpec = mk_inst_spec dfun_name,
+ iBinds = NewTypeDerived ntd_info })) }
+
+ | isNothing mb_std_err -- Use the standard H98 method
+ = do { loc <- getSrcSpanM
+ ; eqn <- mk_data_eqn loc orig tvs cls tycon tc_args rep_tycon rep_tc_args
+ ; return (Just eqn, Nothing) }
+
+ -- Otherwise we can't derive
| gla_exts = baleOut cant_derive_err -- Too hard
- | otherwise = baleOut non_std_err -- Just complain about being a non-std instance
+ | otherwise = baleOut std_err -- Just complain about being a non-std instance
where
+ mb_std_err = checkSideConditions gla_exts cls cls_tys rep_tycon
+ std_err = derivingThingErr cls cls_tys tc_app $
+ vcat [fromJust mb_std_err,
+ ptext SLIT("Try -fglasgow-exts for GHC's newtype-deriving extension")]
+
-- Here is the plan for newtype derivings. We see
-- newtype T a1...an = MkT (t ak+1...an) deriving (.., C s1 .. sm, ...)
-- where t is a type,
cant_derive_err = derivingThingErr cls cls_tys tc_app
(vcat [ptext SLIT("even with cunning newtype deriving:"),
if isRecursiveTyCon tycon then
- ptext SLIT("the newtype is recursive")
+ ptext SLIT("the newtype may be recursive")
else empty,
if not right_arity then
quotes (ppr (mkClassPred cls cls_tys)) <+> ptext SLIT("does not have arity 1")
ptext SLIT("the eta-reduction property does not hold")
else empty
])
-
- non_std_err = derivingThingErr cls cls_tys tc_app
- (vcat [non_std_why cls,
- ptext SLIT("Try -fglasgow-exts for GHC's newtype-deriving extension")])
\end{code}
-- In case of a family instance, we need to use the representation
-- tycon (after all, it has the data constructors)
- ; (tycon, _) <- tcLookupFamInst visible_tycon tyArgs
+ ; (tycon, _) <- tcLookupFamInstExact visible_tycon tyArgs
; let (meth_binds, aux_binds) = genDerivBinds clas fix_env tycon
-- Bring the right type variables into
nest 2 (ptext SLIT("Offending constraint:") <+> ppr pred)]
\end{code}
+
projects / ghc-hetmet.git / blobdiff