tycon tc_args rep_tc rep_tc_args mtheta }
| otherwise
= baleOut (derivingThingErr cls cls_tys tc_app
- (ptext SLIT("Last argument of the instance must be a type application")))
+ (ptext (sLit "Last argument of the instance must be a type application")))
baleOut :: Message -> TcM (Maybe a)
baleOut err = do { addErrTc err; return Nothing }
\end{code}
-Auxiliary lookup wrapper which requires that looked up family instances are
-not type instances. If called with a vanilla tycon, the old type application
-is simply returned.
+Note [Looking up family instances for deriving]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+tcLookupFamInstExact is an auxiliary lookup wrapper which requires
+that looked-up family instances exist. If called with a vanilla
+tycon, the old type application is simply returned.
+
+If we have
+ data instance F () = ... deriving Eq
+ data instance F () = ... deriving Eq
+then tcLookupFamInstExact will be confused by the two matches;
+but that can't happen because tcInstDecls1 doesn't call tcDeriving
+if there are any overlaps.
+
+There are two other things that might go wrong with the lookup.
+First, we might see a standalone deriving clause
+ deriving Eq (F ())
+when there is no data instance F () in scope.
+
+Note that it's OK to have
+ data instance F [a] = ...
+ deriving Eq (F [(a,b)])
+where the match is not exact; the same holds for ordinary data types
+with standalone deriving declrations.
\begin{code}
tcLookupFamInstExact :: TyCon -> [Type] -> TcM (TyCon, [Type])
| otherwise
= do { maybeFamInst <- tcLookupFamInst tycon tys
; case maybeFamInst of
- Nothing -> famInstNotFound tycon tys False
- Just famInst@(_, rep_tys)
- | not variable_only_subst -> famInstNotFound tycon tys True
- | otherwise -> return famInst
- where
- tvs = map (Type.getTyVar
- "TcDeriv.tcLookupFamInstExact")
- rep_tys
- variable_only_subst = all Type.isTyVarTy rep_tys &&
- sizeVarSet (mkVarSet tvs) == length tvs
- -- renaming may have no repetitions
+ Nothing -> famInstNotFound tycon tys
+ Just famInst -> return famInst
}
+
+famInstNotFound :: TyCon -> [Type] -> TcM a
+famInstNotFound tycon tys
+ = failWithTc (ptext (sLit "No family instance for")
+ <+> quotes (pprTypeApp tycon (ppr tycon) tys))
\end{code}
-- Typeable; it depends on the arity of the type
| isNothing mtheta -- deriving on a data type decl
= do { checkTc (cls `hasKey` typeableClassKey)
- (ptext SLIT("Use deriving( Typeable ) on a data type declaration"))
+ (ptext (sLit "Use deriving( Typeable ) on a data type declaration"))
; real_cls <- tcLookupClass (typeableClassNames !! tyConArity tycon)
; mk_typeable_eqn orig tvs real_cls tycon [] rep_tc [] (Just []) }
| otherwise -- standaone deriving
= do { checkTc (null tc_args)
- (ptext SLIT("Derived typeable instance must be of form (Typeable")
+ (ptext (sLit "Derived typeable instance must be of form (Typeable")
<> int (tyConArity tycon) <+> ppr tycon <> rparen)
; dfun_name <- new_dfun_name cls tycon
; loc <- getSrcSpanM
Just cond -> cond (mayDeriveDataTypeable, rep_tc)
Nothing -> Just non_std_why
where
- ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext SLIT("is not a class")
- non_std_why = quotes (ppr cls) <+> ptext SLIT("is not a derivable class")
+ ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "is not a class")
+ non_std_why = quotes (ppr cls) <+> ptext (sLit "is not a derivable class")
sideConditions :: Class -> Maybe Condition
sideConditions cls
Nothing -> Nothing -- c1 succeeds
Just x -> case c2 tc of -- c1 fails
Nothing -> Nothing
- Just y -> Just (x $$ ptext SLIT(" and") $$ y)
+ Just y -> Just (x $$ ptext (sLit " and") $$ y)
-- Both fail
andCond :: Condition -> Condition -> Condition
where
data_cons = tyConDataCons rep_tc
no_cons_why = quotes (pprSourceTyCon rep_tc) <+>
- ptext SLIT("has no data constructors")
+ ptext (sLit "has no data constructors")
existential_why = quotes (pprSourceTyCon rep_tc) <+>
- ptext SLIT("has non-Haskell-98 constructor(s)")
+ ptext (sLit "has non-Haskell-98 constructor(s)")
cond_isEnumeration :: Condition
cond_isEnumeration (_, rep_tc)
| otherwise = Just why
where
why = quotes (pprSourceTyCon rep_tc) <+>
- ptext SLIT("has non-nullary constructors")
+ ptext (sLit "has non-nullary constructors")
cond_isProduct :: Condition
cond_isProduct (_, rep_tc)
| otherwise = Just why
where
why = quotes (pprSourceTyCon rep_tc) <+>
- ptext SLIT("has more than one constructor")
+ ptext (sLit "has more than one constructor")
cond_typeableOK :: Condition
-- OK for Typeable class
| otherwise = Nothing
where
too_many = quotes (pprSourceTyCon rep_tc) <+>
- ptext SLIT("has too many arguments")
+ ptext (sLit "has too many arguments")
bad_kind = quotes (pprSourceTyCon rep_tc) <+>
- ptext SLIT("has arguments of kind other than `*'")
+ ptext (sLit "has arguments of kind other than `*'")
fam_inst = quotes (pprSourceTyCon rep_tc) <+>
- ptext SLIT("is a type family")
+ ptext (sLit "is a type family")
cond_mayDeriveDataTypeable :: Condition
cond_mayDeriveDataTypeable (mayDeriveDataTypeable, _)
| mayDeriveDataTypeable = Nothing
| otherwise = Just why
where
- why = ptext SLIT("You need -XDeriveDataTypeable to derive an instance for this class")
+ why = ptext (sLit "You need -XDeriveDataTypeable to derive an instance for this class")
std_class_via_iso :: Class -> Bool
std_class_via_iso clas -- These standard classes can be derived for a newtype
mb_std_err = checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tycon
std_err = derivingThingErr cls cls_tys tc_app $
vcat [fromJust mb_std_err,
- ptext SLIT("Try -XGeneralizedNewtypeDeriving for GHC's newtype-deriving extension")]
+ ptext (sLit "Try -XGeneralizedNewtypeDeriving 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, ...)
-- arguments must be type variables (not more complex indexes)
cant_derive_err = derivingThingErr cls cls_tys tc_app
- (vcat [ptext SLIT("even with cunning newtype deriving:"),
+ (vcat [ptext (sLit "even with cunning newtype deriving:"),
if isRecursiveTyCon tycon then
- ptext SLIT("the newtype may be 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")
+ quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "does not have arity 1")
else empty,
if not (n_tyargs_to_keep >= 0) then
- ptext SLIT("the type constructor has wrong kind")
+ ptext (sLit "the type constructor has wrong kind")
else if not (n_args_to_keep >= 0) then
- ptext SLIT("the representation type has wrong kind")
+ ptext (sLit "the representation type has wrong kind")
else if not eta_ok then
- ptext SLIT("the eta-reduction property does not hold")
+ ptext (sLit "the eta-reduction property does not hold")
else empty
])
\end{code}
\begin{code}
derivingThingErr :: Class -> [Type] -> Type -> Message -> Message
derivingThingErr clas tys ty why
- = sep [hsep [ptext SLIT("Can't make a derived instance of"),
+ = sep [hsep [ptext (sLit "Can't make a derived instance of"),
quotes (ppr pred)],
nest 2 (parens why)]
where
derivingHiddenErr :: TyCon -> SDoc
derivingHiddenErr tc
- = hang (ptext SLIT("The data constructors of") <+> quotes (ppr tc) <+> ptext SLIT("are not all in scope"))
- 2 (ptext SLIT("so you cannot derive an instance for it"))
+ = hang (ptext (sLit "The data constructors of") <+> quotes (ppr tc) <+> ptext (sLit "are not all in scope"))
+ 2 (ptext (sLit "so you cannot derive an instance for it"))
standaloneCtxt :: LHsType Name -> SDoc
-standaloneCtxt ty = hang (ptext SLIT("In the stand-alone deriving instance for"))
+standaloneCtxt ty = hang (ptext (sLit "In the stand-alone deriving instance for"))
2 (quotes (ppr ty))
derivInstCtxt :: Class -> [Type] -> Message
derivInstCtxt clas inst_tys
- = ptext SLIT("When deriving the instance for") <+> parens (pprClassPred clas inst_tys)
+ = ptext (sLit "When deriving the instance for") <+> parens (pprClassPred clas inst_tys)
badDerivedPred :: PredType -> Message
badDerivedPred pred
- = vcat [ptext SLIT("Can't derive instances where the instance context mentions"),
- ptext SLIT("type variables that are not data type parameters"),
- nest 2 (ptext SLIT("Offending constraint:") <+> ppr pred)]
-
-famInstNotFound :: TyCon -> [Type] -> Bool -> TcM a
-famInstNotFound tycon tys notExact
- = failWithTc (msg <+> quotes (pprTypeApp tycon (ppr tycon) tys))
- where
- msg = ptext $ if notExact
- then SLIT("No family instance exactly matching")
- else SLIT("More than one family instance for")
+ = vcat [ptext (sLit "Can't derive instances where the instance context mentions"),
+ ptext (sLit "type variables that are not data type parameters"),
+ nest 2 (ptext (sLit "Offending constraint:") <+> ppr pred)]
\end{code}
projects / ghc-hetmet.git / blobdiff