Handles @deriving@ clauses on @data@ declarations.
\begin{code}
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+-- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
+-- for details
+
module TcDeriv ( tcDeriving ) where
#include "HsVersions.h"
%************************************************************************
\begin{code}
-tcDeriving :: [LTyClDecl Name] -- All type constructors
+tcDeriving :: [LTyClDecl Name] -- All type constructors
+ -> [LInstDecl Name] -- All instance declarations
-> [LDerivDecl Name] -- All stand-alone deriving declarations
-> TcM ([InstInfo], -- The generated "instance decls"
HsValBinds Name) -- Extra generated top-level bindings
-tcDeriving tycl_decls deriv_decls
+tcDeriving tycl_decls inst_decls deriv_decls
= recoverM (returnM ([], emptyValBindsOut)) $
do { -- Fish the "deriving"-related information out of the TcEnv
-- and make the necessary "equations".
- ; (ordinary_eqns, newtype_inst_info) <- makeDerivEqns tycl_decls deriv_decls
+ ; (ordinary_eqns, newtype_inst_info)
+ <- makeDerivEqns tycl_decls inst_decls deriv_decls
; (ordinary_inst_info, deriv_binds)
<- extendLocalInstEnv (map iSpec newtype_inst_info) $
; gen_binds <- mkGenericBinds tycl_decls
-- Rename these extra bindings, discarding warnings about unused bindings etc
- -- Set -fglasgow exts so that we can have type signatures in patterns,
- -- which is used in the generic binds
+ -- Type signatures in patterns are used in the generic binds
; rn_binds
- <- discardWarnings $ setOptM Opt_GlasgowExts $ do
+ <- discardWarnings $
+ setOptM Opt_PatternSignatures $
+ do
{ (rn_deriv, _dus1) <- rnTopBinds (ValBindsIn deriv_binds [])
; (rn_gen, dus_gen) <- rnTopBinds (ValBindsIn gen_binds [])
; keepAliveSetTc (duDefs dus_gen) -- Mark these guys to
\begin{code}
makeDerivEqns :: [LTyClDecl Name]
+ -> [LInstDecl Name]
-> [LDerivDecl Name]
-> TcM ([DerivEqn], -- Ordinary derivings
[InstInfo]) -- Special newtype derivings
-makeDerivEqns tycl_decls deriv_decls
+makeDerivEqns tycl_decls inst_decls deriv_decls
= do { eqns1 <- mapM deriveTyData $
- [ (p,d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- tycl_decls
- , p <- preds ]
+ extractTyDataPreds tycl_decls ++
+ [ pd -- traverse assoc data families
+ | L _ (InstDecl _ _ _ ats) <- inst_decls
+ , pd <- extractTyDataPreds ats ]
; eqns2 <- mapM deriveStandalone deriv_decls
; return ([eqn | (Just eqn, _) <- eqns1 ++ eqns2],
[inst | (_, Just inst) <- eqns1 ++ eqns2]) }
+ where
+ extractTyDataPreds decls =
+ [(p, d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- decls, p <- preds]
+
------------------------------------------------------------------
deriveStandalone :: LDerivDecl Name -> TcM (Maybe DerivEqn, Maybe InstInfo)
-- Standalone deriving declarations
--- e.g. derive instance Show T
+-- e.g. deriving instance show a => Show (T a)
-- Rather like tcLocalInstDecl
deriveStandalone (L loc (DerivDecl deriv_ty))
= setSrcSpan loc $
addErrCtxt (standaloneCtxt deriv_ty) $
- do { (tvs, theta, tau) <- tcHsInstHead deriv_ty
- ; (cls, inst_tys) <- checkValidInstHead tau
- ; let cls_tys = take (length inst_tys - 1) inst_tys
- inst_ty = last inst_tys
-
- ; mkEqnHelp StandAloneDerivOrigin tvs cls cls_tys inst_ty }
+ do { traceTc (text "standalone deriving decl for" <+> ppr deriv_ty)
+ ; (tvs, theta, tau) <- tcHsInstHead deriv_ty
+ ; traceTc (text "standalone deriving;"
+ <+> text "tvs:" <+> ppr tvs
+ <+> text "theta:" <+> ppr theta
+ <+> text "tau:" <+> ppr tau)
+ ; (cls, inst_tys) <- checkValidInstHead tau
+ ; let cls_tys = take (length inst_tys - 1) inst_tys
+ inst_ty = last inst_tys
+
+ ; traceTc (text "standalone deriving;"
+ <+> text "class:" <+> ppr cls
+ <+> text "class types:" <+> ppr cls_tys
+ <+> text "type:" <+> ppr inst_ty)
+ ; mkEqnHelp StandAloneDerivOrigin tvs cls cls_tys inst_ty
+ (Just theta) }
------------------------------------------------------------------
deriveTyData :: (LHsType Name, LTyClDecl Name) -> TcM (Maybe DerivEqn, Maybe InstInfo)
do { (deriv_tvs, cls, cls_tys) <- tcHsDeriv deriv_pred
-- 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 } }
+ ; mkEqnHelp DerivOrigin (tvs++deriv_tvs) cls cls_tys tc_app Nothing } }
deriveTyData (deriv_pred, other_decl)
= panic "derivTyData" -- Caller ensures that only TyData can happen
------------------------------------------------------------------
-mkEqnHelp orig tvs cls cls_tys tc_app
+mkEqnHelp :: InstOrigin -> [TyVar] -> Class -> [Type] -> Type
+ -> Maybe DerivRhs
+ -> TcRn (Maybe DerivEqn, Maybe InstInfo)
+mkEqnHelp orig tvs cls cls_tys tc_app mtheta
| Just (tycon, tc_args) <- tcSplitTyConApp_maybe tc_app
= do { -- Make tc_app saturated, because that's what the
-- mkDataTypeEqn things expect
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
+ ; mayDeriveDataTypeable <- doptM Opt_DeriveDataTypeable
+ ; newtype_deriving <- doptM Opt_GeneralizedNewtypeDeriving
; overlap_flag <- getOverlapFlag
- ; if isDataTyCon tycon then
- mkDataTypeEqn orig gla_exts full_tvs cls cls_tys
- tycon full_tc_args rep_tc rep_tc_args
+
+ -- 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 mayDeriveDataTypeable full_tvs cls cls_tys
+ tycon full_tc_args rep_tc rep_tc_args mtheta
else
- mkNewTypeEqn orig gla_exts overlap_flag full_tvs cls cls_tys
- tycon full_tc_args rep_tc rep_tc_args }
+ mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving overlap_flag
+ full_tvs cls cls_tys
+ tycon full_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")))
baleOut err = addErrTc err >> returnM (Nothing, 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.
+
+\begin{code}
+tcLookupFamInstExact :: TyCon -> [Type] -> TcM (TyCon, [Type])
+tcLookupFamInstExact tycon tys
+ | not (isOpenTyCon tycon)
+ = return (tycon, tys)
+ | 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
+ }
+\end{code}
+
%************************************************************************
%* *
%************************************************************************
\begin{code}
-mkDataTypeEqn orig gla_exts tvs cls cls_tys tycon tc_args rep_tc rep_tc_args
- | Just err <- checkSideConditions gla_exts cls cls_tys rep_tc
+mkDataTypeEqn :: InstOrigin -> Bool -> [Var] -> Class -> [Type]
+ -> TyCon -> [Type] -> TyCon -> [Type] -> Maybe DerivRhs
+ -> TcRn (Maybe DerivEqn, Maybe InstInfo)
+mkDataTypeEqn orig mayDeriveDataTypeable tvs cls cls_tys
+ tycon tc_args rep_tc rep_tc_args mtheta
+ | Just err <- checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc
-- NB: pass the *representation* tycon to checkSideConditions
= baleOut (derivingThingErr cls cls_tys (mkTyConApp tycon tc_args) err)
| otherwise
= ASSERT( null cls_tys )
do { loc <- getSrcSpanM
- ; eqn <- mk_data_eqn loc orig tvs cls tycon tc_args rep_tc rep_tc_args
+ ; eqn <- mk_data_eqn loc orig tvs cls tycon tc_args rep_tc
+ rep_tc_args mtheta
; return (Just eqn, Nothing) }
mk_data_eqn :: SrcSpan -> InstOrigin -> [TyVar] -> Class
- -> TyCon -> [TcType] -> TyCon -> [TcType] -> TcM DerivEqn
-mk_data_eqn loc orig tvs cls tycon tc_args rep_tc rep_tc_args
+ -> TyCon -> [TcType] -> TyCon -> [TcType] -> Maybe DerivRhs
+ -> TcM DerivEqn
+mk_data_eqn loc orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
| cls `hasKey` typeableClassKey
= -- The Typeable class is special in several ways
-- data T a b = ... deriving( Typeable )
-- Typeable; it depends on the arity of the type
do { real_clas <- tcLookupClass (typeableClassNames !! tyConArity tycon)
; dfun_name <- new_dfun_name real_clas tycon
- ; return (loc, orig, dfun_name, [], real_clas, mkTyConApp tycon [], []) }
+ ; let theta = fromMaybe [] mtheta
+ ; return (loc, orig, dfun_name, [], real_clas, mkTyConApp tycon [], theta)
+ }
| otherwise
= do { dfun_name <- new_dfun_name cls tycon
; let ordinary_constraints
= [ mkClassPred cls [arg_ty]
| data_con <- tyConDataCons rep_tc,
- arg_ty <- dataConInstOrigArgTys data_con rep_tc_args,
+ arg_ty <- ASSERT( isVanillaDataCon data_con )
+ dataConInstOrigArgTys data_con rep_tc_args,
not (isUnLiftedType arg_ty) ] -- No constraints for unlifted types?
+ theta = fromMaybe ordinary_constraints mtheta
tiresome_subst = zipTopTvSubst (tyConTyVars rep_tc) rep_tc_args
stupid_constraints = substTheta tiresome_subst (tyConStupidTheta rep_tc)
-- see note [Data decl contexts] above
; return (loc, orig, dfun_name, tvs, cls, mkTyConApp tycon tc_args,
- stupid_constraints ++ ordinary_constraints)
+ stupid_constraints ++ theta)
}
------------------------------------------------------------------
-- family tycon (with indexes) in error messages.
checkSideConditions :: Bool -> Class -> [TcType] -> TyCon -> Maybe SDoc
-checkSideConditions gla_exts cls cls_tys rep_tc
+checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc
| notNull cls_tys
= Just ty_args_why -- e.g. deriving( Foo s )
| otherwise
= case [cond | (key,cond) <- sideConditions, key == getUnique cls] of
[] -> Just (non_std_why cls)
- [cond] -> cond (gla_exts, rep_tc)
+ [cond] -> cond (mayDeriveDataTypeable, rep_tc)
other -> pprPanic "checkSideConditions" (ppr cls)
where
ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext SLIT("is not a class")
(enumClassKey, cond_std `andCond` cond_isEnumeration),
(ixClassKey, cond_std `andCond` (cond_isEnumeration `orCond` cond_isProduct)),
(boundedClassKey, cond_std `andCond` (cond_isEnumeration `orCond` cond_isProduct)),
- (typeableClassKey, cond_glaExts `andCond` cond_typeableOK),
- (dataClassKey, cond_glaExts `andCond` cond_std)
+ (typeableClassKey, cond_mayDeriveDataTypeable `andCond` cond_typeableOK),
+ (dataClassKey, cond_mayDeriveDataTypeable `andCond` cond_std)
]
type Condition = (Bool, TyCon) -> Maybe SDoc
- -- Bool is gla-exts flag
+ -- Bool is whether or not we are allowed to derive Data and Typeable
-- TyCon is the *representation* tycon if the
-- data type is an indexed one
-- Nothing => OK
Just x -> Just x -- c1 fails
cond_std :: Condition
-cond_std (gla_exts, rep_tc)
+cond_std (_, rep_tc)
| any (not . isVanillaDataCon) data_cons = Just existential_why
| null data_cons = Just no_cons_why
| otherwise = Nothing
ptext SLIT("has non-Haskell-98 constructor(s)")
cond_isEnumeration :: Condition
-cond_isEnumeration (gla_exts, rep_tc)
+cond_isEnumeration (_, rep_tc)
| isEnumerationTyCon rep_tc = Nothing
| otherwise = Just why
where
ptext SLIT("has non-nullary constructors")
cond_isProduct :: Condition
-cond_isProduct (gla_exts, rep_tc)
+cond_isProduct (_, rep_tc)
| isProductTyCon rep_tc = Nothing
| otherwise = Just why
where
-- OK for Typeable class
-- Currently: (a) args all of kind *
-- (b) 7 or fewer args
-cond_typeableOK (gla_exts, rep_tc)
+cond_typeableOK (_, rep_tc)
| tyConArity rep_tc > 7 = Just too_many
| not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars rep_tc))
= Just bad_kind
fam_inst = quotes (pprSourceTyCon rep_tc) <+>
ptext SLIT("is a type family")
-cond_glaExts :: Condition
-cond_glaExts (gla_exts, _rep_tc) | gla_exts = Nothing
- | otherwise = Just why
+cond_mayDeriveDataTypeable :: Condition
+cond_mayDeriveDataTypeable (mayDeriveDataTypeable, _)
+ | mayDeriveDataTypeable = Nothing
+ | otherwise = Just why
where
why = ptext SLIT("You need -fglasgow-exts to derive an instance for this class")
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}
%************************************************************************
\begin{code}
-mkNewTypeEqn orig gla_exts overlap_flag tvs cls cls_tys
- tycon tc_args
- rep_tycon rep_tc_args
- | can_derive_via_isomorphism && (gla_exts || std_class_via_iso cls)
+mkNewTypeEqn :: InstOrigin -> Bool -> Bool -> OverlapFlag -> [Var] -> Class
+ -> [Type] -> TyCon -> [Type] -> TyCon -> [Type]
+ -> Maybe DerivRhs
+ -> TcRn (Maybe DerivEqn, Maybe InstInfo)
+mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving overlap_flag tvs
+ cls cls_tys tycon tc_args rep_tycon rep_tc_args mtheta
+ | can_derive_via_isomorphism && (newtype_deriving || 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
| 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
+ ; eqn <- mk_data_eqn loc orig tvs cls tycon tc_args rep_tycon
+ rep_tc_args mtheta
; return (Just eqn, Nothing) }
-- Otherwise we can't derive
- | gla_exts = baleOut cant_derive_err -- Too hard
+ | newtype_deriving = baleOut cant_derive_err -- Too hard
| otherwise = baleOut std_err -- Just complain about being a non-std instance
where
- mb_std_err = checkSideConditions gla_exts cls cls_tys rep_tycon
+ 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 -fglasgow-exts 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, ...)
gen_soln :: DerivEqn -> TcM [PredType]
gen_soln (loc, orig, _, tyvars, clas, inst_ty, deriv_rhs)
= setSrcSpan loc $
+ addErrCtxt (derivInstCtxt clas [inst_ty]) $
do { theta <- tcSimplifyDeriv orig tyvars deriv_rhs
- ; addErrCtxt (derivInstCtxt theta clas [inst_ty]) $
- do { checkNoErrs (checkValidInstance tyvars theta clas [inst_ty])
- -- See Note [Deriving context]
- -- If this fails, don't continue
+ -- checkValidInstance tyvars theta clas [inst_ty]
+ -- Not necessary; see Note [Exotic derived instance contexts]
+ -- in TcSimplify
-- Check for a bizarre corner case, when the derived instance decl should
-- have form instance C a b => D (T a) where ...
-- Claim: the result instance declaration is guaranteed valid
-- Hence no need to call:
-- checkValidInstance tyvars theta clas inst_tys
- ; return (sortLe (<=) theta) } } -- Canonicalise before returning the solution
+ ; return (sortLe (<=) theta) } -- Canonicalise before returning the solution
------------------------------------------------------------------
mk_inst_spec :: DerivEqn -> DerivSoln -> Instance
; setGblEnv env' thing_inside }
\end{code}
-Note [Deriving context]
-~~~~~~~~~~~~~~~~~~~~~~~
-With -fglasgow-exts, we allow things like (C Int a) in the simplified
-context for a derived instance declaration, because at a use of this
-instance, we might know that a=Bool, and have an instance for (C Int
-Bool)
-
-We nevertheless insist that each predicate meets the termination
-conditions. If not, the deriving mechanism generates larger and larger
-constraints. Example:
- data Succ a = S a
- data Seq a = Cons a (Seq (Succ a)) | Nil deriving Show
-
-Note the lack of a Show instance for Succ. First we'll generate
- instance (Show (Succ a), Show a) => Show (Seq a)
-and then
- instance (Show (Succ (Succ a)), Show (Succ a), Show a) => Show (Seq a)
-and so on. Instead we want to complain of no instance for (Show (Succ a)).
-
%************************************************************************
%* *
-- 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
standaloneCtxt :: LHsType Name -> SDoc
standaloneCtxt ty = ptext SLIT("In the stand-alone deriving instance for") <+> quotes (ppr ty)
-derivInstCtxt theta clas inst_tys
- = hang (ptext SLIT("In the derived instance:"))
- 2 (pprThetaArrow theta <+> pprClassPred clas inst_tys)
--- Used for the ...Thetas variants; all top level
+derivInstCtxt clas inst_tys
+ = ptext SLIT("When deriving the instance for") <+> parens (pprClassPred clas inst_tys)
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)]
-\end{code}
-
\ No newline at end of file
+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")
+\end{code}
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