%
% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
Handles @deriving@ clauses on @data@ declarations.
\begin{code}
module TcDeriv ( tcDeriving ) where
#include "HsVersions.h"
import HsSyn
import DynFlags
import Generics
import TcRnMonad
import TcEnv
import TcClassDcl( tcAddDeclCtxt )
import TcGenDeriv
import InstEnv
import Inst
import TcHsType
import TcMType
import TcSimplify
import RnBinds
import RnEnv
import HscTypes
import Class
import Type
import Coercion
import ErrUtils
import MkId
import DataCon
import Maybes
import RdrName
import Name
import NameSet
import TyCon
import TcType
import BuildTyCl
import BasicTypes
import Var
import VarSet
import PrelNames
import SrcLoc
import UniqSupply
import Util
import ListSetOps
import Outputable
import FastString
import Bag
import Control.Monad
\end{code}
%************************************************************************
%* *
Overview
%* *
%************************************************************************
Overall plan
~~~~~~~~~~~~
1. Convert the decls (i.e. data/newtype deriving clauses,
plus standalone deriving) to [EarlyDerivSpec]
2. Infer the missing contexts for the Left DerivSpecs
3. Add the derived bindings, generating InstInfos
\begin{code}
data DerivSpec = DS { ds_loc :: SrcSpan
, ds_orig :: CtOrigin
, ds_name :: Name
, ds_tvs :: [TyVar]
, ds_theta :: ThetaType
, ds_cls :: Class
, ds_tys :: [Type]
, ds_tc :: TyCon
, ds_tc_args :: [Type]
, ds_newtype :: Bool }
\end{code}
Example:
newtype instance T [a] = MkT (Tree a) deriving( C s )
==>
axiom T [a] = :RTList a
axiom :RTList a = Tree a
DS { ds_tvs = [a,s], ds_cls = C, ds_tys = [s, T [a]]
, ds_tc = :RTList, ds_tc_args = [a]
, ds_newtype = True }
\begin{code}
type DerivContext = Maybe ThetaType
type EarlyDerivSpec = Either DerivSpec DerivSpec
pprDerivSpec :: DerivSpec -> SDoc
pprDerivSpec (DS { ds_loc = l, ds_name = n, ds_tvs = tvs,
ds_cls = c, ds_tys = tys, ds_theta = rhs })
= parens (hsep [ppr l, ppr n, ppr tvs, ppr c, ppr tys]
<+> equals <+> ppr rhs)
instance Outputable DerivSpec where
ppr = pprDerivSpec
\end{code}
Inferring missing contexts
~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
data T a b = C1 (Foo a) (Bar b)
| C2 Int (T b a)
| C3 (T a a)
deriving (Eq)
[NOTE: See end of these comments for what to do with
data (C a, D b) => T a b = ...
]
We want to come up with an instance declaration of the form
instance (Ping a, Pong b, ...) => Eq (T a b) where
x == y = ...
It is pretty easy, albeit tedious, to fill in the code "...". The
trick is to figure out what the context for the instance decl is,
namely @Ping@, @Pong@ and friends.
Let's call the context reqd for the T instance of class C at types
(a,b, ...) C (T a b). Thus:
Eq (T a b) = (Ping a, Pong b, ...)
Now we can get a (recursive) equation from the @data@ decl:
Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
u Eq (T b a) u Eq Int -- From C2
u Eq (T a a) -- From C3
Foo and Bar may have explicit instances for @Eq@, in which case we can
just substitute for them. Alternatively, either or both may have
their @Eq@ instances given by @deriving@ clauses, in which case they
form part of the system of equations.
Now all we need do is simplify and solve the equations, iterating to
find the least fixpoint. Notice that the order of the arguments can
switch around, as here in the recursive calls to T.
Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
We start with:
Eq (T a b) = {} -- The empty set
Next iteration:
Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
u Eq (T b a) u Eq Int -- From C2
u Eq (T a a) -- From C3
After simplification:
= Eq a u Ping b u {} u {} u {}
= Eq a u Ping b
Next iteration:
Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
u Eq (T b a) u Eq Int -- From C2
u Eq (T a a) -- From C3
After simplification:
= Eq a u Ping b
u (Eq b u Ping a)
u (Eq a u Ping a)
= Eq a u Ping b u Eq b u Ping a
The next iteration gives the same result, so this is the fixpoint. We
need to make a canonical form of the RHS to ensure convergence. We do
this by simplifying the RHS to a form in which
- the classes constrain only tyvars
- the list is sorted by tyvar (major key) and then class (minor key)
- no duplicates, of course
So, here are the synonyms for the ``equation'' structures:
Note [Data decl contexts]
~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
We will need an instance decl like:
instance (Read a, RealFloat a) => Read (Complex a) where
...
The RealFloat in the context is because the read method for Complex is bound
to construct a Complex, and doing that requires that the argument type is
in RealFloat.
But this ain't true for Show, Eq, Ord, etc, since they don't construct
a Complex; they only take them apart.
Our approach: identify the offending classes, and add the data type
context to the instance decl. The "offending classes" are
Read, Enum?
FURTHER NOTE ADDED March 2002. In fact, Haskell98 now requires that
pattern matching against a constructor from a data type with a context
gives rise to the constraints for that context -- or at least the thinned
version. So now all classes are "offending".
Note [Newtype deriving]
~~~~~~~~~~~~~~~~~~~~~~~
Consider this:
class C a b
instance C [a] Char
newtype T = T Char deriving( C [a] )
Notice the free 'a' in the deriving. We have to fill this out to
newtype T = T Char deriving( forall a. C [a] )
And then translate it to:
instance C [a] Char => C [a] T where ...
Note [Newtype deriving superclasses]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
(See also Trac #1220 for an interesting exchange on newtype
deriving and superclasses.)
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 isomorphism; 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 may be a coercion needed which we get from the tycon for the newtype
when the dict is constructed in TcInstDcls.tcInstDecl2
Note [Unused constructors and deriving clauses]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
See Trac #3221. Consider
data T = T1 | T2 deriving( Show )
Are T1 and T2 unused? Well, no: the deriving clause expands to mention
both of them. So we gather defs/uses from deriving just like anything else.
%************************************************************************
%* *
\subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
%* *
%************************************************************************
\begin{code}
tcDeriving :: [LTyClDecl Name]
-> [LInstDecl Name]
-> [LDerivDecl Name]
-> TcM ([InstInfo Name]
,HsValBinds Name
,DefUses
,[TyCon]
,[TyCon])
tcDeriving tycl_decls inst_decls deriv_decls
= recoverM (return ([], emptyValBindsOut, emptyDUs, [], [])) $
do {
is_boot <- tcIsHsBoot
; traceTc "tcDeriving" (ppr is_boot)
; (early_specs, genericsExtras)
<- makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls
; let (repMetaTys, repTyCons, metaInsts) = unzip3 genericsExtras
; overlap_flag <- getOverlapFlag
; let (infer_specs, given_specs) = splitEithers early_specs
; insts1 <- mapM (genInst True overlap_flag) given_specs
; final_specs <- extendLocalInstEnv (map (iSpec . fst) insts1) $
inferInstanceContexts overlap_flag infer_specs
; insts2 <- mapM (genInst False overlap_flag) final_specs
; gen_binds <- return emptyBag
; (inst_info, rn_binds, rn_dus)
<- renameDeriv is_boot gen_binds (insts1 ++ insts2 ++ concat metaInsts)
; dflags <- getDOpts
; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
(ddump_deriving inst_info rn_binds repMetaTys repTyCons metaInsts))
; return ( inst_info, rn_binds, rn_dus
, concat (map metaTyCons2TyCons repMetaTys), repTyCons) }
where
ddump_deriving :: [InstInfo Name] -> HsValBinds Name
-> [MetaTyCons]
-> [TyCon]
-> [[(InstInfo RdrName, DerivAuxBinds)]]
-> SDoc
ddump_deriving inst_infos extra_binds repMetaTys repTyCons metaInsts
= hang (ptext (sLit "Derived instances"))
2 (vcat (map (\i -> pprInstInfoDetails i $$ text "") inst_infos)
$$ ppr extra_binds)
$$ hangP "Generic representation" (
hangP "Generated datatypes for meta-information"
(vcat (map ppr repMetaTys))
$$ hangP "Representation types"
(vcat (map ppr repTyCons))
$$ hangP "Meta-information instances"
(vcat (map (pprInstInfoDetails . fst) (concat metaInsts))))
hangP s x = text "" $$ hang (ptext (sLit s)) 2 x
renameDeriv :: Bool -> LHsBinds RdrName
-> [(InstInfo RdrName, DerivAuxBinds)]
-> TcM ([InstInfo Name], HsValBinds Name, DefUses)
renameDeriv is_boot gen_binds insts
| is_boot
= do { (rn_inst_infos, fvs) <- mapAndUnzipM rn_inst_info inst_infos
; return (rn_inst_infos, emptyValBindsOut, usesOnly (plusFVs fvs)) }
| otherwise
= discardWarnings $
do { (rn_gen, dus_gen) <- setXOptM Opt_ScopedTypeVariables $
rnTopBinds (ValBindsIn gen_binds [])
; keepAliveSetTc (duDefs dus_gen)
; loc <- getSrcSpanM
; let (aux_binds, aux_sigs) = unzip $ map (genAuxBind loc) $
rm_dups [] $ concat deriv_aux_binds
aux_val_binds = ValBindsIn (listToBag aux_binds) aux_sigs
; rn_aux_lhs <- rnTopBindsLHS emptyFsEnv aux_val_binds
; bindLocalNames (collectHsValBinders rn_aux_lhs) $
do { (rn_aux, dus_aux) <- rnTopBindsRHS rn_aux_lhs
; (rn_inst_infos, fvs_insts) <- mapAndUnzipM rn_inst_info inst_infos
; return (rn_inst_infos, rn_aux `plusHsValBinds` rn_gen,
dus_gen `plusDU` dus_aux `plusDU` usesOnly (plusFVs fvs_insts)) } }
where
(inst_infos, deriv_aux_binds) = unzip insts
rm_dups acc [] = acc
rm_dups acc (b:bs) | any (isDupAux b) acc = rm_dups acc bs
| otherwise = rm_dups (b:acc) bs
rn_inst_info :: InstInfo RdrName -> TcM (InstInfo Name, FreeVars)
rn_inst_info info@(InstInfo { iBinds = NewTypeDerived coi tc })
= return ( info { iBinds = NewTypeDerived coi tc }
, mkFVs (map dataConName (tyConDataCons tc)))
rn_inst_info inst_info@(InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs standalone_deriv })
=
ASSERT( null sigs )
bindLocalNames (map Var.varName tyvars) $
do { (rn_binds, fvs) <- rnMethodBinds clas_nm (\_ -> []) binds
; let binds' = VanillaInst rn_binds [] standalone_deriv
; return (inst_info { iBinds = binds' }, fvs) }
where
(tyvars,_, clas,_) = instanceHead inst
clas_nm = className clas
\end{code}
Note [Newtype deriving and unused constructors]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this (see Trac #1954):
module Bug(P) where
newtype P a = MkP (IO a) deriving Monad
If you compile with -fwarn-unused-binds you do not expect the warning
"Defined but not used: data consructor MkP". Yet the newtype deriving
code does not explicitly mention MkP, but it should behave as if you
had written
instance Monad P where
return x = MkP (return x)
...etc...
So we want to signal a user of the data constructor 'MkP'. That's
what we do in rn_inst_info, and it's the only reason we have the TyCon
stored in NewTypeDerived.
%************************************************************************
%* *
From HsSyn to DerivSpec
%* *
%************************************************************************
@makeDerivSpecs@ fishes around to find the info about needed derived instances.
\begin{code}
mkGenDerivExtras :: TyCon
-> TcRn (MetaTyCons, TyCon, [(InstInfo RdrName, DerivAuxBinds)])
mkGenDerivExtras tc = do
{ (metaTyCons, rep0TyInst) <- genGenericRepExtras tc
; metaInsts <- genDtMeta (tc, metaTyCons)
; return (metaTyCons, rep0TyInst, metaInsts) }
makeDerivSpecs :: Bool
-> [LTyClDecl Name]
-> [LInstDecl Name]
-> [LDerivDecl Name]
-> TcM ( [EarlyDerivSpec]
, [(MetaTyCons, TyCon, [(InstInfo RdrName, DerivAuxBinds)])])
makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls
| is_boot
= do { mapM_ add_deriv_err deriv_locs
; return ([],[]) }
| otherwise
= do { eqns1 <- mapAndRecoverM deriveTyData all_tydata
; eqns2 <- mapAndRecoverM deriveStandalone deriv_decls
; xDerRep <- getDOpts >>= return . xopt Opt_DeriveGeneric
; generic_extras_deriv <- if not xDerRep
then (return [])
else do {
let allTyNames = [ tcdName d | L _ d <- tycl_decls, isDataDecl d ]
; let sel_tydata = [ tcdName t | (L _ c, L _ t) <- all_tydata
, getClassName c == Just genClassName ]
; let sel_deriv_decls = catMaybes [ getTypeName t
| L _ (DerivDecl (L _ t)) <- deriv_decls
, getClassName t == Just genClassName ]
; derTyDecls <- mapM tcLookupTyCon $
filter (needsExtras xDerRep
(sel_tydata ++ sel_deriv_decls)) allTyNames
;
mapM mkGenDerivExtras derTyDecls }
; return ( eqns1 ++ eqns2, generic_extras_deriv) }
where
needsExtras xDerRep tydata tc_name = xDerRep && tc_name `elem` tydata
getClassName :: HsType Name -> Maybe Name
getClassName (HsForAllTy _ _ _ (L _ n)) = getClassName n
getClassName (HsPredTy (HsClassP n _)) = Just n
getClassName _ = Nothing
getTypeName :: HsType Name -> Maybe Name
getTypeName (HsForAllTy _ _ _ (L _ n)) = getTypeName n
getTypeName (HsTyVar n) = Just n
getTypeName (HsOpTy _ (L _ n) _) = Just n
getTypeName (HsPredTy (HsClassP _ [L _ n])) = getTypeName n
getTypeName (HsAppTy (L _ n) _) = getTypeName n
getTypeName (HsParTy (L _ n)) = getTypeName n
getTypeName (HsKindSig (L _ n) _) = getTypeName n
getTypeName _ = Nothing
extractTyDataPreds decls
= [(p, d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- decls, p <- preds]
all_tydata :: [(LHsType Name, LTyClDecl Name)]
all_tydata = extractTyDataPreds (instDeclATs inst_decls ++ tycl_decls)
deriv_locs = map (getLoc . snd) all_tydata
++ map getLoc deriv_decls
add_deriv_err loc = setSrcSpan loc $
addErr (hang (ptext (sLit "Deriving not permitted in hs-boot file"))
2 (ptext (sLit "Use an instance declaration instead")))
deriveStandalone :: LDerivDecl Name -> TcM EarlyDerivSpec
deriveStandalone (L loc (DerivDecl deriv_ty))
= setSrcSpan loc $
addErrCtxt (standaloneCtxt deriv_ty) $
do { traceTc "Standalone deriving decl for" (ppr deriv_ty)
; (tvs, theta, cls, inst_tys) <- tcHsInstHead deriv_ty
; traceTc "Standalone deriving;" $ vcat
[ text "tvs:" <+> ppr tvs
, text "theta:" <+> ppr theta
, text "cls:" <+> ppr cls
, text "tys:" <+> ppr inst_tys ]
; checkValidInstance deriv_ty tvs theta cls inst_tys
; let cls_tys = take (length inst_tys 1) inst_tys
inst_ty = last inst_tys
; traceTc "Standalone deriving:" $ vcat
[ 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 EarlyDerivSpec
deriveTyData (L loc deriv_pred, L _ decl@(TyData { tcdLName = L _ tycon_name,
tcdTyVars = tv_names,
tcdTyPats = ty_pats }))
= setSrcSpan loc $
tcAddDeclCtxt decl $
do { (tvs, tc, tc_args) <- get_lhs ty_pats
; tcExtendTyVarEnv tvs $
do { (deriv_tvs, cls, cls_tys) <- tcHsDeriv deriv_pred
; let cls_tyvars = classTyVars cls
kind = tyVarKind (last cls_tyvars)
(arg_kinds, _) = splitKindFunTys kind
n_args_to_drop = length arg_kinds
n_args_to_keep = tyConArity tc n_args_to_drop
args_to_drop = drop n_args_to_keep tc_args
inst_ty = mkTyConApp tc (take n_args_to_keep tc_args)
inst_ty_kind = typeKind inst_ty
dropped_tvs = mkVarSet (mapCatMaybes getTyVar_maybe args_to_drop)
univ_tvs = (mkVarSet tvs `extendVarSetList` deriv_tvs)
`minusVarSet` dropped_tvs
; checkTc (n_args_to_keep >= 0 && (inst_ty_kind `eqKind` kind))
(derivingKindErr tc cls cls_tys kind)
; checkTc (sizeVarSet dropped_tvs == n_args_to_drop &&
tyVarsOfTypes (inst_ty:cls_tys) `subVarSet` univ_tvs)
(derivingEtaErr cls cls_tys inst_ty)
; checkTc (not (isFamilyTyCon tc) || n_args_to_drop == 0)
(typeFamilyPapErr tc cls cls_tys inst_ty)
; mkEqnHelp DerivOrigin (varSetElems univ_tvs) cls cls_tys inst_ty Nothing } }
where
get_lhs Nothing = do { tc <- tcLookupTyCon tycon_name
; let tvs = tyConTyVars tc
; return (tvs, tc, mkTyVarTys tvs) }
get_lhs (Just pats) = do { let hs_app = nlHsTyConApp tycon_name pats
; (tvs, tc_app) <- tcHsQuantifiedType tv_names hs_app
; let (tc, tc_args) = tcSplitTyConApp tc_app
; return (tvs, tc, tc_args) }
deriveTyData _other
= panic "derivTyData"
\end{code}
Note [Deriving, type families, and partial applications]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When there are no type families, it's quite easy:
newtype S a = MkS [a]
-- :CoS :: S ~ [] -- Eta-reduced
instance Eq [a] => Eq (S a) -- by coercion sym (Eq (:CoS a)) : Eq [a] ~ Eq (S a)
instance Monad [] => Monad S -- by coercion sym (Monad :CoS) : Monad [] ~ Monad S
When type familes are involved it's trickier:
data family T a b
newtype instance T Int a = MkT [a] deriving( Eq, Monad )
-- :RT is the representation type for (T Int a)
-- :CoF:R1T a :: T Int a ~ :RT a -- Not eta reduced
-- :Co:R1T :: :RT ~ [] -- Eta-reduced
instance Eq [a] => Eq (T Int a) -- easy by coercion
instance Monad [] => Monad (T Int) -- only if we can eta reduce???
The "???" bit is that we don't build the :CoF thing in eta-reduced form
Henc the current typeFamilyPapErr, even though the instance makes sense.
After all, we can write it out
instance Monad [] => Monad (T Int) -- only if we can eta reduce???
return x = MkT [x]
... etc ...
\begin{code}
mkEqnHelp :: CtOrigin -> [TyVar] -> Class -> [Type] -> Type
-> DerivContext
-> TcRn EarlyDerivSpec
mkEqnHelp orig tvs cls cls_tys tc_app mtheta
| Just (tycon, tc_args) <- tcSplitTyConApp_maybe tc_app
, isAlgTyCon tycon
= mk_alg_eqn tycon tc_args
| otherwise
= failWithTc (derivingThingErr False cls cls_tys tc_app
(ptext (sLit "The last argument of the instance must be a data or newtype application")))
where
bale_out msg = failWithTc (derivingThingErr False cls cls_tys tc_app msg)
mk_alg_eqn tycon tc_args
| className cls `elem` typeableClassNames
= do { dflags <- getDOpts
; case checkTypeableConditions (dflags, tycon) of
Just err -> bale_out err
Nothing -> mk_typeable_eqn orig tvs cls tycon tc_args mtheta }
| isDataFamilyTyCon tycon
, length tc_args /= tyConArity tycon
= bale_out (ptext (sLit "Unsaturated data family application"))
| otherwise
= do { (rep_tc, rep_tc_args) <- tcLookupDataFamInst tycon tc_args
; rdr_env <- getGlobalRdrEnv
; let hidden_data_cons = isAbstractTyCon rep_tc ||
any not_in_scope (tyConDataCons rep_tc)
not_in_scope dc = null (lookupGRE_Name rdr_env (dataConName dc))
; unless (isNothing mtheta || not hidden_data_cons)
(bale_out (derivingHiddenErr tycon))
; dflags <- getDOpts
; if isDataTyCon rep_tc then
mkDataTypeEqn orig dflags tvs cls cls_tys
tycon tc_args rep_tc rep_tc_args mtheta
else
mkNewTypeEqn orig dflags tvs cls cls_tys
tycon tc_args rep_tc rep_tc_args mtheta }
\end{code}
%************************************************************************
%* *
Deriving data types
%* *
%************************************************************************
\begin{code}
mkDataTypeEqn :: CtOrigin
-> DynFlags
-> [Var]
-> Class
-> [Type]
-> TyCon
-> [Type]
-> TyCon
-> [Type]
-> DerivContext
-> TcRn EarlyDerivSpec
mkDataTypeEqn orig dflags tvs cls cls_tys
tycon tc_args rep_tc rep_tc_args mtheta
= case checkSideConditions dflags mtheta cls cls_tys rep_tc of
CanDerive -> go_for_it
NonDerivableClass -> bale_out (nonStdErr cls)
DerivableClassError msg -> bale_out msg
where
go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
bale_out msg = failWithTc (derivingThingErr False cls cls_tys (mkTyConApp tycon tc_args) msg)
mk_data_eqn :: CtOrigin -> [TyVar] -> Class
-> TyCon -> [TcType] -> TyCon -> [TcType] -> DerivContext
-> TcM EarlyDerivSpec
mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
= do { dfun_name <- new_dfun_name cls tycon
; loc <- getSrcSpanM
; let inst_tys = [mkTyConApp tycon tc_args]
inferred_constraints = inferConstraints tvs cls inst_tys rep_tc rep_tc_args
spec = DS { ds_loc = loc, ds_orig = orig
, ds_name = dfun_name, ds_tvs = tvs
, ds_cls = cls, ds_tys = inst_tys
, ds_tc = rep_tc, ds_tc_args = rep_tc_args
, ds_theta = mtheta `orElse` inferred_constraints
, ds_newtype = False }
; return (if isJust mtheta then Right spec
else Left spec) }
mk_typeable_eqn :: CtOrigin -> [TyVar] -> Class
-> TyCon -> [TcType] -> DerivContext
-> TcM EarlyDerivSpec
mk_typeable_eqn orig tvs cls tycon tc_args mtheta
| isNothing mtheta
= do { checkTc (cls `hasKey` typeableClassKey)
(ptext (sLit "Use deriving( Typeable ) on a data type declaration"))
; real_cls <- tcLookupClass (typeableClassNames !! tyConArity tycon)
; mk_typeable_eqn orig tvs real_cls tycon [] (Just []) }
| otherwise
= do { checkTc (null tc_args)
(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
; return (Right $
DS { ds_loc = loc, ds_orig = orig, ds_name = dfun_name, ds_tvs = []
, ds_cls = cls, ds_tys = [mkTyConApp tycon []]
, ds_tc = tycon, ds_tc_args = []
, ds_theta = mtheta `orElse` [], ds_newtype = False }) }
inferConstraints :: [TyVar] -> Class -> [TcType] -> TyCon -> [TcType] -> ThetaType
inferConstraints _ cls inst_tys rep_tc rep_tc_args
| cls `hasKey` genClassKey
= []
| otherwise
= ASSERT2( equalLength rep_tc_tvs all_rep_tc_args, ppr cls <+> ppr rep_tc )
stupid_constraints ++ extra_constraints
++ sc_constraints ++ con_arg_constraints
where
con_arg_constraints
= [ mkClassPred cls [arg_ty]
| data_con <- tyConDataCons rep_tc,
arg_ty <- ASSERT( isVanillaDataCon data_con )
get_constrained_tys $
dataConInstOrigArgTys data_con all_rep_tc_args,
not (isUnLiftedType arg_ty) ]
is_functor_like = getUnique cls `elem` functorLikeClassKeys
get_constrained_tys :: [Type] -> [Type]
get_constrained_tys tys
| is_functor_like = concatMap (deepSubtypesContaining last_tv) tys
| otherwise = tys
rep_tc_tvs = tyConTyVars rep_tc
last_tv = last rep_tc_tvs
all_rep_tc_args | is_functor_like = rep_tc_args ++ [mkTyVarTy last_tv]
| otherwise = rep_tc_args
sc_constraints = substTheta (zipOpenTvSubst (classTyVars cls) inst_tys)
(classSCTheta cls)
stupid_constraints = substTheta subst (tyConStupidTheta rep_tc)
subst = zipTopTvSubst rep_tc_tvs all_rep_tc_args
extra_constraints
| cls `hasKey` dataClassKey
, all (isLiftedTypeKind . typeKind) rep_tc_args
= [mkClassPred cls [ty] | ty <- rep_tc_args]
| otherwise
= []
data DerivStatus = CanDerive
| DerivableClassError SDoc
| NonDerivableClass
checkSideConditions :: DynFlags -> DerivContext -> Class -> [TcType] -> TyCon -> DerivStatus
checkSideConditions dflags mtheta cls cls_tys rep_tc
| Just cond <- sideConditions mtheta cls
= case (cond (dflags, rep_tc)) of
Just err -> DerivableClassError err
Nothing | null cls_tys -> CanDerive
| otherwise -> DerivableClassError ty_args_why
| otherwise = NonDerivableClass
where
ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "is not a class")
checkTypeableConditions :: Condition
checkTypeableConditions = checkFlag Opt_DeriveDataTypeable `andCond` cond_typeableOK
nonStdErr :: Class -> SDoc
nonStdErr cls = quotes (ppr cls) <+> ptext (sLit "is not a derivable class")
sideConditions :: DerivContext -> Class -> Maybe Condition
sideConditions mtheta cls
| cls_key == eqClassKey = Just cond_std
| cls_key == ordClassKey = Just cond_std
| cls_key == showClassKey = Just cond_std
| cls_key == readClassKey = Just (cond_std `andCond` cond_noUnliftedArgs)
| cls_key == enumClassKey = Just (cond_std `andCond` cond_isEnumeration)
| cls_key == ixClassKey = Just (cond_std `andCond` cond_enumOrProduct)
| cls_key == boundedClassKey = Just (cond_std `andCond` cond_enumOrProduct)
| cls_key == dataClassKey = Just (checkFlag Opt_DeriveDataTypeable `andCond`
cond_std `andCond` cond_noUnliftedArgs)
| cls_key == functorClassKey = Just (checkFlag Opt_DeriveFunctor `andCond`
cond_functorOK True)
| cls_key == foldableClassKey = Just (checkFlag Opt_DeriveFoldable `andCond`
cond_functorOK False)
| cls_key == traversableClassKey = Just (checkFlag Opt_DeriveTraversable `andCond`
cond_functorOK False)
| cls_key == genClassKey = Just (cond_RepresentableOk `andCond`
checkFlag Opt_DeriveGeneric)
| otherwise = Nothing
where
cls_key = getUnique cls
cond_std = cond_stdOK mtheta
type Condition = (DynFlags, TyCon) -> Maybe SDoc
orCond :: Condition -> Condition -> Condition
orCond c1 c2 tc
= case c1 tc of
Nothing -> Nothing
Just x -> case c2 tc of
Nothing -> Nothing
Just y -> Just (x $$ ptext (sLit " or") $$ y)
andCond :: Condition -> Condition -> Condition
andCond c1 c2 tc = case c1 tc of
Nothing -> c2 tc
Just x -> Just x
cond_stdOK :: DerivContext -> Condition
cond_stdOK (Just _) _
= Nothing
cond_stdOK Nothing (_, rep_tc)
| null data_cons = Just (no_cons_why rep_tc $$ suggestion)
| not (null con_whys) = Just (vcat con_whys $$ suggestion)
| otherwise = Nothing
where
suggestion = ptext (sLit "Possible fix: use a standalone deriving declaration instead")
data_cons = tyConDataCons rep_tc
con_whys = mapCatMaybes check_con data_cons
check_con :: DataCon -> Maybe SDoc
check_con con
| isVanillaDataCon con
, all isTauTy (dataConOrigArgTys con) = Nothing
| otherwise = Just (badCon con (ptext (sLit "must have a Haskell-98 type")))
no_cons_why :: TyCon -> SDoc
no_cons_why rep_tc = quotes (pprSourceTyCon rep_tc) <+>
ptext (sLit "must have at least one data constructor")
cond_RepresentableOk :: Condition
cond_RepresentableOk (_,t) = canDoGenerics t
cond_enumOrProduct :: Condition
cond_enumOrProduct = cond_isEnumeration `orCond`
(cond_isProduct `andCond` cond_noUnliftedArgs)
cond_noUnliftedArgs :: Condition
cond_noUnliftedArgs (_, tc)
| null bad_cons = Nothing
| otherwise = Just why
where
bad_cons = [ con | con <- tyConDataCons tc
, any isUnLiftedType (dataConOrigArgTys con) ]
why = badCon (head bad_cons) (ptext (sLit "must have only arguments of lifted type"))
cond_isEnumeration :: Condition
cond_isEnumeration (_, rep_tc)
| isEnumerationTyCon rep_tc = Nothing
| otherwise = Just why
where
why = sep [ quotes (pprSourceTyCon rep_tc) <+>
ptext (sLit "must be an enumeration type")
, ptext (sLit "(an enumeration consists of one or more nullary, non-GADT constructors)") ]
cond_isProduct :: Condition
cond_isProduct (_, rep_tc)
| isProductTyCon rep_tc = Nothing
| otherwise = Just why
where
why = quotes (pprSourceTyCon rep_tc) <+>
ptext (sLit "must have precisely one constructor")
cond_typeableOK :: Condition
cond_typeableOK (_, tc)
| tyConArity tc > 7 = Just too_many
| not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars tc))
= Just bad_kind
| otherwise = Nothing
where
too_many = quotes (pprSourceTyCon tc) <+>
ptext (sLit "must have 7 or fewer arguments")
bad_kind = quotes (pprSourceTyCon tc) <+>
ptext (sLit "must only have arguments of kind `*'")
functorLikeClassKeys :: [Unique]
functorLikeClassKeys = [functorClassKey, foldableClassKey, traversableClassKey]
cond_functorOK :: Bool -> Condition
cond_functorOK allowFunctions (_, rep_tc)
| null tc_tvs
= Just (ptext (sLit "Data type") <+> quotes (ppr rep_tc)
<+> ptext (sLit "must have some type parameters"))
| not (null bad_stupid_theta)
= Just (ptext (sLit "Data type") <+> quotes (ppr rep_tc)
<+> ptext (sLit "must not have a class context") <+> pprTheta bad_stupid_theta)
| otherwise
= msum (map check_con data_cons)
where
tc_tvs = tyConTyVars rep_tc
Just (_, last_tv) = snocView tc_tvs
bad_stupid_theta = filter is_bad (tyConStupidTheta rep_tc)
is_bad pred = last_tv `elemVarSet` tyVarsOfPred pred
data_cons = tyConDataCons rep_tc
check_con con = msum (check_vanilla con : foldDataConArgs (ft_check con) con)
check_vanilla :: DataCon -> Maybe SDoc
check_vanilla con | isVanillaDataCon con = Nothing
| otherwise = Just (badCon con existential)
ft_check :: DataCon -> FFoldType (Maybe SDoc)
ft_check con = FT { ft_triv = Nothing, ft_var = Nothing
, ft_co_var = Just (badCon con covariant)
, ft_fun = \x y -> if allowFunctions then x `mplus` y
else Just (badCon con functions)
, ft_tup = \_ xs -> msum xs
, ft_ty_app = \_ x -> x
, ft_bad_app = Just (badCon con wrong_arg)
, ft_forall = \_ x -> x }
existential = ptext (sLit "must not have existential arguments")
covariant = ptext (sLit "must not use the type variable in a function argument")
functions = ptext (sLit "must not contain function types")
wrong_arg = ptext (sLit "must not use the type variable in an argument other than the last")
checkFlag :: ExtensionFlag -> Condition
checkFlag flag (dflags, _)
| xopt flag dflags = Nothing
| otherwise = Just why
where
why = ptext (sLit "You need -X") <> text flag_str
<+> ptext (sLit "to derive an instance for this class")
flag_str = case [ s | (s, _, f, _) <- xFlags, f==flag ] of
[s] -> s
other -> pprPanic "checkFlag" (ppr other)
std_class_via_iso :: Class -> Bool
std_class_via_iso clas
= classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey]
non_iso_class :: Class -> Bool
non_iso_class cls
= classKey cls `elem` ([ readClassKey, showClassKey, dataClassKey
, genClassKey] ++ typeableClassKeys)
typeableClassKeys :: [Unique]
typeableClassKeys = map getUnique typeableClassNames
new_dfun_name :: Class -> TyCon -> TcM Name
new_dfun_name clas tycon
= do { loc <- getSrcSpanM
; newDFunName clas [mkTyConApp tycon []] loc }
badCon :: DataCon -> SDoc -> SDoc
badCon con msg = ptext (sLit "Constructor") <+> quotes (ppr con) <+> msg
\end{code}
Note [Superclasses of derived instance]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In general, a derived instance decl needs the superclasses of the derived
class too. So if we have
data T a = ...deriving( Ord )
then the initial context for Ord (T a) should include Eq (T a). Often this is
redundant; we'll also generate an Ord constraint for each constructor argument,
and that will probably generate enough constraints to make the Eq (T a) constraint
be satisfied too. But not always; consider:
data S a = S
instance Eq (S a)
instance Ord (S a)
data T a = MkT (S a) deriving( Ord )
instance Num a => Eq (T a)
The derived instance for (Ord (T a)) must have a (Num a) constraint!
Similarly consider:
data T a = MkT deriving( Data, Typeable )
Here there *is* no argument field, but we must nevertheless generate
a context for the Data instances:
instance Typable a => Data (T a) where ...
%************************************************************************
%* *
Deriving newtypes
%* *
%************************************************************************
\begin{code}
mkNewTypeEqn :: CtOrigin -> DynFlags -> [Var] -> Class
-> [Type] -> TyCon -> [Type] -> TyCon -> [Type]
-> DerivContext
-> TcRn EarlyDerivSpec
mkNewTypeEqn orig dflags 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 "newtype deriving:" (ppr tycon <+> ppr rep_tys <+> ppr all_preds)
; dfun_name <- new_dfun_name cls tycon
; loc <- getSrcSpanM
; let spec = DS { ds_loc = loc, ds_orig = orig
, ds_name = dfun_name, ds_tvs = varSetElems dfun_tvs
, ds_cls = cls, ds_tys = inst_tys
, ds_tc = rep_tycon, ds_tc_args = rep_tc_args
, ds_theta = mtheta `orElse` all_preds
, ds_newtype = True }
; return (if isJust mtheta then Right spec
else Left spec) }
| otherwise
= case checkSideConditions dflags mtheta cls cls_tys rep_tycon of
CanDerive -> go_for_it
DerivableClassError msg
| can_derive_via_isomorphism -> bale_out (msg $$ suggest_nd)
| otherwise -> bale_out msg
NonDerivableClass
| newtype_deriving -> bale_out cant_derive_err
| can_derive_via_isomorphism -> bale_out (non_std $$ suggest_nd)
| otherwise -> bale_out non_std
where
newtype_deriving = xopt Opt_GeneralizedNewtypeDeriving dflags
go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tycon rep_tc_args mtheta
bale_out msg = failWithTc (derivingThingErr newtype_deriving cls cls_tys inst_ty msg)
non_std = nonStdErr cls
suggest_nd = ptext (sLit "Try -XGeneralizedNewtypeDeriving for GHC's newtype-deriving extension")
nt_eta_arity = length (fst (newTyConEtadRhs rep_tycon))
rep_inst_ty = newTyConInstRhs rep_tycon rep_tc_args
rep_tys = cls_tys ++ [rep_inst_ty]
rep_pred = mkClassPred cls rep_tys
cls_tyvars = classTyVars cls
dfun_tvs = tyVarsOfTypes inst_tys
inst_ty = mkTyConApp tycon tc_args
inst_tys = cls_tys ++ [inst_ty]
sc_theta = substTheta (zipOpenTvSubst cls_tyvars inst_tys)
(classSCTheta cls)
all_preds = rep_pred : sc_theta
can_derive_via_isomorphism
= not (non_iso_class cls)
&& arity_ok
&& eta_ok
&& ats_ok
arity_ok = length cls_tys + 1 == classArity cls
eta_ok = nt_eta_arity <= length rep_tc_args
ats_ok = null (classATs cls)
cant_derive_err
= vcat [ ppUnless arity_ok arity_msg
, ppUnless eta_ok eta_msg
, ppUnless ats_ok ats_msg ]
arity_msg = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "does not have arity 1")
eta_msg = ptext (sLit "cannot eta-reduce the representation type enough")
ats_msg = ptext (sLit "the class has associated types")
\end{code}
Note [Recursive newtypes]
~~~~~~~~~~~~~~~~~~~~~~~~~
Newtype deriving works fine, even if the newtype is recursive.
e.g. newtype S1 = S1 [T1 ()]
newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad )
Remember, too, that type families are curretly (conservatively) given
a recursive flag, so this also allows newtype deriving to work
for type famillies.
We used to exclude recursive types, because we had a rather simple
minded way of generating the instance decl:
newtype A = MkA [A]
instance Eq [A] => Eq A -- Makes typechecker loop!
But now we require a simple context, so it's ok.
%************************************************************************
%* *
\subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
%* *
%************************************************************************
A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
terms, which is the final correct RHS for the corresponding original
equation.
\begin{itemize}
\item
Each (k,TyVarTy tv) in a solution constrains only a type
variable, tv.
\item
The (k,TyVarTy tv) pairs in a solution are canonically
ordered by sorting on type varible, tv, (major key) and then class, k,
(minor key)
\end{itemize}
\begin{code}
inferInstanceContexts :: OverlapFlag -> [DerivSpec] -> TcM [DerivSpec]
inferInstanceContexts _ [] = return []
inferInstanceContexts oflag infer_specs
= do { traceTc "inferInstanceContexts" $ vcat (map pprDerivSpec infer_specs)
; iterate_deriv 1 initial_solutions }
where
initial_solutions :: [ThetaType]
initial_solutions = [ [] | _ <- infer_specs ]
iterate_deriv :: Int -> [ThetaType] -> TcM [DerivSpec]
iterate_deriv n current_solns
| n > 20
= pprPanic "solveDerivEqns: probable loop"
(vcat (map pprDerivSpec infer_specs) $$ ppr current_solns)
| otherwise
= do {
let inst_specs = zipWithEqual "add_solns" (mkInstance oflag)
current_solns infer_specs
; new_solns <- checkNoErrs $
extendLocalInstEnv inst_specs $
mapM gen_soln infer_specs
; if (current_solns == new_solns) then
return [ spec { ds_theta = soln }
| (spec, soln) <- zip infer_specs current_solns ]
else
iterate_deriv (n+1) new_solns }
gen_soln :: DerivSpec -> TcM [PredType]
gen_soln (DS { ds_loc = loc, ds_orig = orig, ds_tvs = tyvars
, ds_cls = clas, ds_tys = inst_tys, ds_theta = deriv_rhs })
= setSrcSpan loc $
addErrCtxt (derivInstCtxt the_pred) $
do {
; let tv_set = mkVarSet tyvars
weird_preds = [pred | pred <- deriv_rhs
, not (tyVarsOfPred pred `subVarSet` tv_set)]
; mapM_ (addErrTc . badDerivedPred) weird_preds
; theta <- simplifyDeriv orig the_pred tyvars deriv_rhs
; traceTc "TcDeriv" (ppr deriv_rhs $$ ppr theta)
; return (sortLe (<=) theta) }
where
the_pred = mkClassPred clas inst_tys
mkInstance :: OverlapFlag -> ThetaType -> DerivSpec -> Instance
mkInstance overlap_flag theta
(DS { ds_name = dfun_name
, ds_tvs = tyvars, ds_cls = clas, ds_tys = tys })
= mkLocalInstance dfun overlap_flag
where
dfun = mkDictFunId dfun_name tyvars theta clas tys
extendLocalInstEnv :: [Instance] -> TcM a -> TcM a
extendLocalInstEnv dfuns thing_inside
= do { env <- getGblEnv
; let inst_env' = extendInstEnvList (tcg_inst_env env) dfuns
env' = env { tcg_inst_env = inst_env' }
; setGblEnv env' thing_inside }
\end{code}
%************************************************************************
%* *
\subsection[TcDeriv-normal-binds]{Bindings for the various classes}
%* *
%************************************************************************
After all the trouble to figure out the required context for the
derived instance declarations, all that's left is to chug along to
produce them. They will then be shoved into @tcInstDecls2@, which
will do all its usual business.
There are lots of possibilities for code to generate. Here are
various general remarks.
PRINCIPLES:
\begin{itemize}
\item
We want derived instances of @Eq@ and @Ord@ (both v common) to be
``you-couldn't-do-better-by-hand'' efficient.
\item
Deriving @Show@---also pretty common--- should also be reasonable good code.
\item
Deriving for the other classes isn't that common or that big a deal.
\end{itemize}
PRAGMATICS:
\begin{itemize}
\item
Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
\item
Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
\item
We {\em normally} generate code only for the non-defaulted methods;
there are some exceptions for @Eq@ and (especially) @Ord@...
\item
Sometimes we use a @_con2tag_@ function, which returns a data
constructor's numeric (@Int#@) tag. These are generated by
@gen_tag_n_con_binds@, and the heuristic for deciding if one of
these is around is given by @hasCon2TagFun@.
The examples under the different sections below will make this
clearer.
\item
Much less often (really just for deriving @Ix@), we use a
@_tag2con_@ function. See the examples.
\item
We use the renamer!!! Reason: we're supposed to be
producing @LHsBinds Name@ for the methods, but that means
producing correctly-uniquified code on the fly. This is entirely
possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
So, instead, we produce @MonoBinds RdrName@ then heave 'em through
the renamer. What a great hack!
\end{itemize}
\begin{code}
genInst :: Bool
-> OverlapFlag
-> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds)
genInst standalone_deriv oflag
spec@(DS { ds_tc = rep_tycon, ds_tc_args = rep_tc_args
, ds_theta = theta, ds_newtype = is_newtype
, ds_name = name, ds_cls = clas })
| is_newtype
= return (InstInfo { iSpec = inst_spec
, iBinds = NewTypeDerived co rep_tycon }, [])
| otherwise
= do { fix_env <- getFixityEnv
; let loc = getSrcSpan name
(meth_binds, aux_binds) = genDerivBinds loc fix_env clas rep_tycon
; return (InstInfo { iSpec = inst_spec
, iBinds = VanillaInst meth_binds [] standalone_deriv }
, aux_binds) }
where
inst_spec = mkInstance oflag theta spec
co1 = case tyConFamilyCoercion_maybe rep_tycon of
Just co_con -> mkAxInstCo co_con rep_tc_args
Nothing -> id_co
co2 = mkAxInstCo (newTyConCo rep_tycon) rep_tc_args
co = co1 `mkTransCo` co2
id_co = mkReflCo (mkTyConApp rep_tycon rep_tc_args)
genDerivBinds :: SrcSpan -> FixityEnv -> Class -> TyCon -> (LHsBinds RdrName, DerivAuxBinds)
genDerivBinds loc fix_env clas tycon
| className clas `elem` typeableClassNames
= (gen_Typeable_binds loc tycon, [])
| otherwise
= case assocMaybe gen_list (getUnique clas) of
Just gen_fn -> gen_fn loc tycon
Nothing -> pprPanic "genDerivBinds: bad derived class" (ppr clas)
where
gen_list :: [(Unique, SrcSpan -> TyCon -> (LHsBinds RdrName, DerivAuxBinds))]
gen_list = [(eqClassKey, gen_Eq_binds)
,(ordClassKey, gen_Ord_binds)
,(enumClassKey, gen_Enum_binds)
,(boundedClassKey, gen_Bounded_binds)
,(ixClassKey, gen_Ix_binds)
,(showClassKey, gen_Show_binds fix_env)
,(readClassKey, gen_Read_binds fix_env)
,(dataClassKey, gen_Data_binds)
,(functorClassKey, gen_Functor_binds)
,(foldableClassKey, gen_Foldable_binds)
,(traversableClassKey, gen_Traversable_binds)
,(genClassKey, genGenericBinds)
]
\end{code}
%************************************************************************
%* *
\subsection[TcDeriv-generic-binds]{Bindings for the new generic deriving mechanism}
%* *
%************************************************************************
For the generic representation we need to generate:
\begin{itemize}
\item A Generic instance
\item A Rep type instance
\item Many auxiliary datatypes and instances for them (for the meta-information)
\end{itemize}
@genGenericBinds@ does (1)
@genGenericRepExtras@ does (2) and (3)
@genGenericAll@ does all of them
\begin{code}
genGenericBinds :: SrcSpan -> TyCon -> (LHsBinds RdrName, DerivAuxBinds)
genGenericBinds _ tc = (mkBindsRep tc, [ ])
genGenericRepExtras :: TyCon -> TcM (MetaTyCons, TyCon)
genGenericRepExtras tc =
do uniqS <- newUniqueSupply
let
(uniqD:uniqs) = uniqsFromSupply uniqS
(uniqsC,us) = splitAt (length tc_cons) uniqs
uniqsS :: [[Unique]]
uniqsS = mkUniqsS tc_arits us
mkUniqsS [] _ = []
mkUniqsS (n:t) us = case splitAt n us of
(us1,us2) -> us1 : mkUniqsS t us2
tc_name = tyConName tc
tc_cons = tyConDataCons tc
tc_arits = map dataConSourceArity tc_cons
tc_occ = nameOccName tc_name
d_occ = mkGenD tc_occ
c_occ m = mkGenC tc_occ m
s_occ m n = mkGenS tc_occ m n
mod_name = nameModule (tyConName tc)
d_name = mkExternalName uniqD mod_name d_occ wiredInSrcSpan
c_names = [ mkExternalName u mod_name (c_occ m) wiredInSrcSpan
| (u,m) <- zip uniqsC [0..] ]
s_names = [ [ mkExternalName u mod_name (s_occ m n) wiredInSrcSpan
| (u,n) <- zip us [0..] ] | (us,m) <- zip uniqsS [0..] ]
mkTyCon name = ASSERT( isExternalName name )
buildAlgTyCon name [] [] mkAbstractTyConRhs
NonRecursive False NoParentTyCon Nothing
metaDTyCon <- mkTyCon d_name
metaCTyCons <- sequence [ mkTyCon c_name | c_name <- c_names ]
metaSTyCons <- mapM sequence
[ [ mkTyCon s_name
| s_name <- s_namesC ] | s_namesC <- s_names ]
let metaDts = MetaTyCons metaDTyCon metaCTyCons metaSTyCons
rep0_tycon <- tc_mkRepTyCon tc metaDts
return (metaDts, rep0_tycon)
genDtMeta :: (TyCon, MetaTyCons) -> TcM [(InstInfo RdrName, DerivAuxBinds)]
genDtMeta (tc,metaDts) =
do dflags <- getDOpts
dClas <- tcLookupClass datatypeClassName
d_dfun_name <- new_dfun_name dClas tc
cClas <- tcLookupClass constructorClassName
c_dfun_names <- sequence [ new_dfun_name cClas tc | _ <- metaC metaDts ]
sClas <- tcLookupClass selectorClassName
s_dfun_names <- sequence (map sequence [ [ new_dfun_name sClas tc
| _ <- x ]
| x <- metaS metaDts ])
fix_env <- getFixityEnv
let
safeOverlap = safeLanguageOn dflags
(dBinds,cBinds,sBinds) = mkBindsMetaD fix_env tc
d_metaTycon = metaD metaDts
d_inst = mkLocalInstance d_dfun $ NoOverlap safeOverlap
d_binds = VanillaInst dBinds [] False
d_dfun = mkDictFunId d_dfun_name (tyConTyVars tc) [] dClas
[ mkTyConTy d_metaTycon ]
d_mkInst = (InstInfo { iSpec = d_inst, iBinds = d_binds }, [])
c_metaTycons = metaC metaDts
c_insts = [ mkLocalInstance (c_dfun c ds) $ NoOverlap safeOverlap
| (c, ds) <- myZip1 c_metaTycons c_dfun_names ]
c_binds = [ VanillaInst c [] False | c <- cBinds ]
c_dfun c dfun_name = mkDictFunId dfun_name (tyConTyVars tc) [] cClas
[ mkTyConTy c ]
c_mkInst = [ (InstInfo { iSpec = is, iBinds = bs }, [])
| (is,bs) <- myZip1 c_insts c_binds ]
s_metaTycons = metaS metaDts
s_insts = map (map (\(s,ds) -> mkLocalInstance (s_dfun s ds) $
NoOverlap safeOverlap))
(myZip2 s_metaTycons s_dfun_names)
s_binds = [ [ VanillaInst s [] False | s <- ss ] | ss <- sBinds ]
s_dfun s dfun_name = mkDictFunId dfun_name (tyConTyVars tc) [] sClas
[ mkTyConTy s ]
s_mkInst = map (map (\(is,bs) -> (InstInfo {iSpec=is, iBinds=bs}, [])))
(myZip2 s_insts s_binds)
myZip1 :: [a] -> [b] -> [(a,b)]
myZip1 l1 l2 = ASSERT (length l1 == length l2) zip l1 l2
myZip2 :: [[a]] -> [[b]] -> [[(a,b)]]
myZip2 l1 l2 =
ASSERT (and (zipWith (>=) (map length l1) (map length l2)))
[ zip x1 x2 | (x1,x2) <- zip l1 l2 ]
return (d_mkInst : c_mkInst ++ concat s_mkInst)
\end{code}
%************************************************************************
%* *
\subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
%* *
%************************************************************************
\begin{code}
derivingKindErr :: TyCon -> Class -> [Type] -> Kind -> Message
derivingKindErr tc cls cls_tys cls_kind
= hang (ptext (sLit "Cannot derive well-kinded instance of form")
<+> quotes (pprClassPred cls cls_tys <+> parens (ppr tc <+> ptext (sLit "..."))))
2 (ptext (sLit "Class") <+> quotes (ppr cls)
<+> ptext (sLit "expects an argument of kind") <+> quotes (pprKind cls_kind))
derivingEtaErr :: Class -> [Type] -> Type -> Message
derivingEtaErr cls cls_tys inst_ty
= sep [ptext (sLit "Cannot eta-reduce to an instance of form"),
nest 2 (ptext (sLit "instance (...) =>")
<+> pprClassPred cls (cls_tys ++ [inst_ty]))]
typeFamilyPapErr :: TyCon -> Class -> [Type] -> Type -> Message
typeFamilyPapErr tc cls cls_tys inst_ty
= hang (ptext (sLit "Derived instance") <+> quotes (pprClassPred cls (cls_tys ++ [inst_ty])))
2 (ptext (sLit "requires illegal partial application of data type family") <+> ppr tc)
derivingThingErr :: Bool -> Class -> [Type] -> Type -> Message -> Message
derivingThingErr newtype_deriving clas tys ty why
= sep [(hang (ptext (sLit "Can't make a derived instance of"))
2 (quotes (ppr pred))
$$ nest 2 extra) <> colon,
nest 2 why]
where
extra | newtype_deriving = ptext (sLit "(even with cunning newtype deriving)")
| otherwise = empty
pred = mkClassPred clas (tys ++ [ty])
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"))
standaloneCtxt :: LHsType Name -> SDoc
standaloneCtxt ty = hang (ptext (sLit "In the stand-alone deriving instance for"))
2 (quotes (ppr ty))
derivInstCtxt :: PredType -> Message
derivInstCtxt pred
= ptext (sLit "When deriving the instance for") <+> parens (ppr pred)
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)]
\end{code}