.
%************************************************************************
%* *
\subsection{Extracting instance decls}
%* *
%************************************************************************
Gather up the instance declarations from their various sources
\begin{code}
tcInstDecls1
:: [LTyClDecl Name]
-> [LInstDecl Name]
-> [LDerivDecl Name]
-> TcM (TcGblEnv,
[InstInfo Name],
HsValBinds Name)
tcInstDecls1 tycl_decls inst_decls deriv_decls
= checkNoErrs $
do {
; env <- getGblEnv
; stuff <- mapAndRecoverM tcLocalInstDecl inst_decls
; let (local_infos_s, fam_insts_s) = unzip stuff
fam_insts = concat fam_insts_s
local_infos' = concat local_infos_s
(typeable_instances, local_infos) = splitTypeable env local_infos'
; addClsInsts local_infos $
addFamInsts fam_insts $
do {
failIfErrsM
; traceTc "tcDeriving" empty
; th_stage <- getStage
; (gbl_env, deriv_inst_info, deriv_binds)
<- if isBrackStage th_stage
then do { gbl_env <- getGblEnv
; return (gbl_env, emptyBag, emptyValBindsOut) }
else tcDeriving tycl_decls inst_decls deriv_decls
; mapM_ (failWithTc . instMsg) typeable_instances
; dflags <- getDynFlags
; when (safeLanguageOn dflags) $
mapM_ (\x -> when (typInstCheck x)
(addErrAt (getSrcSpan $ iSpec x) typInstErr))
local_infos
; when (safeInferOn dflags) $
mapM_ (\x -> when (typInstCheck x) recordUnsafeInfer) local_infos
; return ( gbl_env
, bagToList deriv_inst_info ++ local_infos
, deriv_binds)
}}
where
splitTypeable _ [] = ([],[])
splitTypeable env (i:is) =
let (typeableInsts, otherInsts) = splitTypeable env is
in if
(typeableClassName == is_cls_nm (iSpec i))
&& tcg_mod env /= tYPEABLE_INTERNAL
&& not (isHsBoot (tcg_src env))
then (i:typeableInsts, otherInsts)
else (typeableInsts, i:otherInsts)
typInstCheck ty = is_cls_nm (iSpec ty) `elem` oldTypeableClassNames
typInstErr = ptext $ sLit $ "Can't create hand written instances of Typeable in Safe"
++ " Haskell! Can only derive them"
instMsg i = hang (ptext (sLit $ "Typeable instances can only be derived; replace "
++ "the following instance:"))
2 (pprInstance (iSpec i))
addClsInsts :: [InstInfo Name] -> TcM a -> TcM a
addClsInsts infos thing_inside
= tcExtendLocalInstEnv (map iSpec infos) thing_inside
addFamInsts :: [FamInst] -> TcM a -> TcM a
addFamInsts fam_insts thing_inside
= tcExtendLocalFamInstEnv fam_insts $
tcExtendGlobalEnv things $
do { traceTc "addFamInsts" (pprFamInsts fam_insts)
; tcg_env <- tcAddImplicits things
; setGblEnv tcg_env thing_inside }
where
axioms = map (toBranchedAxiom . famInstAxiom) fam_insts
tycons = famInstsRepTyCons fam_insts
things = map ATyCon tycons ++ map ACoAxiom axioms
\end{code}
Note [Deriving inside TH brackets]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Given a declaration bracket
[d| data T = A | B deriving( Show ) |]
there is really no point in generating the derived code for deriving(
Show) and then type-checking it. This will happen at the call site
anyway, and the type check should never fail! Moreover (Trac #6005)
the scoping of the generated code inside the bracket does not seem to
work out.
The easy solution is simply not to generate the derived instances at
all. (A less brutal solution would be to generate them with no
bindings.) This will become moot when we shift to the new TH plan, so
the brutal solution will do.
\begin{code}
tcLocalInstDecl :: LInstDecl Name
-> TcM ([InstInfo Name], [FamInst])
tcLocalInstDecl (L loc (TyFamInstD { tfid_inst = decl }))
= do { fam_inst <- tcTyFamInstDecl Nothing (L loc decl)
; return ([], [fam_inst]) }
tcLocalInstDecl (L loc (DataFamInstD { dfid_inst = decl }))
= do { fam_inst <- tcDataFamInstDecl Nothing (L loc decl)
; return ([], [fam_inst]) }
tcLocalInstDecl (L loc (ClsInstD { cid_inst = decl }))
= do { (insts, fam_insts) <- tcClsInstDecl (L loc decl)
; return (insts, fam_insts) }
tcClsInstDecl :: LClsInstDecl Name -> TcM ([InstInfo Name], [FamInst])
tcClsInstDecl (L loc (ClsInstDecl { cid_poly_ty = poly_ty, cid_binds = binds
, cid_sigs = uprags, cid_tyfam_insts = ats
, cid_datafam_insts = adts }))
= setSrcSpan loc $
addErrCtxt (instDeclCtxt1 poly_ty) $
do { is_boot <- tcIsHsBoot
; checkTc (not is_boot || (isEmptyLHsBinds binds && null uprags))
badBootDeclErr
; (tyvars, theta, clas, inst_tys) <- tcHsInstHead InstDeclCtxt poly_ty
; let mini_env = mkVarEnv (classTyVars clas `zip` inst_tys)
mini_subst = mkTvSubst (mkInScopeSet (mkVarSet tyvars)) mini_env
mb_info = Just (clas, mini_env)
; traceTc "tcLocalInstDecl" (ppr poly_ty)
; tyfam_insts0 <- tcExtendTyVarEnv tyvars $
mapAndRecoverM (tcAssocTyDecl clas mini_env) ats
; datafam_insts <- tcExtendTyVarEnv tyvars $
mapAndRecoverM (tcDataFamInstDecl mb_info) adts
; let defined_ats = mkNameSet $ map (tyFamInstDeclName . unLoc) ats
defined_adts = mkNameSet $ map (unLoc . dfid_tycon . unLoc) adts
mk_deflt_at_instances :: ClassATItem -> TcM [FamInst]
mk_deflt_at_instances (fam_tc, defs)
| tyConName fam_tc `elemNameSet` defined_ats
|| tyConName fam_tc `elemNameSet` defined_adts
= return []
| null defs
= do { warnMissingMethodOrAT "associated type" (tyConName fam_tc)
; return [] }
| otherwise
= forM defs $ \(CoAxBranch { cab_lhs = pat_tys, cab_rhs = rhs }) ->
do { let pat_tys' = substTys mini_subst pat_tys
rhs' = substTy mini_subst rhs
tv_set' = tyVarsOfTypes pat_tys'
tvs' = varSetElems tv_set'
; rep_tc_name <- newFamInstTyConName (noLoc (tyConName fam_tc)) pat_tys'
; let axiom = mkSingleCoAxiom rep_tc_name tvs' fam_tc pat_tys' rhs'
; ASSERT( tyVarsOfType rhs' `subVarSet` tv_set' )
newFamInst SynFamilyInst axiom }
; tyfam_insts1 <- mapM mk_deflt_at_instances (classATItems clas)
; dfun_name <- newDFunName clas inst_tys (getLoc poly_ty)
; overlap_flag <- getOverlapFlag
; (subst, tyvars') <- tcInstSkolTyVars tyvars
; let dfun = mkDictFunId dfun_name tyvars theta clas inst_tys
ispec = mkLocalInstance dfun overlap_flag tyvars' clas (substTys subst inst_tys)
inst_info = InstInfo { iSpec = ispec
, iBinds = InstBindings
{ ib_binds = binds
, ib_pragmas = uprags
, ib_standalone_deriving = False } }
; return ( [inst_info], tyfam_insts0 ++ concat tyfam_insts1 ++ datafam_insts) }
tcAssocTyDecl :: Class
-> VarEnv Type
-> LTyFamInstDecl Name
-> TcM (FamInst)
tcAssocTyDecl clas mini_env ldecl
= do { fam_inst <- tcTyFamInstDecl (Just (clas, mini_env)) ldecl
; return fam_inst }
\end{code}
%************************************************************************
%* *
Type checking family instances
%* *
%************************************************************************
Family instances are somewhat of a hybrid. They are processed together with
class instance heads, but can contain data constructors and hence they share a
lot of kinding and type checking code with ordinary algebraic data types (and
GADTs).
\begin{code}
tcFamInstDeclCombined :: Maybe (Class, VarEnv Type)
-> Located Name -> TcM TyCon
tcFamInstDeclCombined mb_clsinfo fam_tc_lname
= do {
; traceTc "tcFamInstDecl" (ppr fam_tc_lname)
; type_families <- xoptM Opt_TypeFamilies
; is_boot <- tcIsHsBoot
; checkTc type_families $ badFamInstDecl fam_tc_lname
; checkTc (not is_boot) $ badBootFamInstDeclErr
; fam_tc <- tcLookupLocatedTyCon fam_tc_lname
; when (isNothing mb_clsinfo &&
isTyConAssoc fam_tc)
(addErr $ assocInClassErr fam_tc_lname)
; return fam_tc }
tcTyFamInstDecl :: Maybe (Class, VarEnv Type)
-> LTyFamInstDecl Name -> TcM FamInst
tcTyFamInstDecl mb_clsinfo (L loc decl@(TyFamInstDecl { tfid_eqn = eqn }))
= setSrcSpan loc $
tcAddTyFamInstCtxt decl $
do { let fam_lname = tfie_tycon (unLoc eqn)
; fam_tc <- tcFamInstDeclCombined mb_clsinfo fam_lname
; checkTc (isFamilyTyCon fam_tc) (notFamily fam_tc)
; checkTc (isSynTyCon fam_tc) (wrongKindOfFamily fam_tc)
; checkTc (isOpenSynFamilyTyCon fam_tc)
(notOpenFamily fam_tc)
; co_ax_branch <- tcSynFamInstDecl fam_tc decl
; checkValidTyFamInst mb_clsinfo fam_tc co_ax_branch
; rep_tc_name <- newFamInstAxiomName loc
(tyFamInstDeclName decl)
[co_ax_branch]
; let axiom = mkUnbranchedCoAxiom rep_tc_name fam_tc co_ax_branch
; newFamInst SynFamilyInst axiom }
tcDataFamInstDecl :: Maybe (Class, VarEnv Type)
-> LDataFamInstDecl Name -> TcM FamInst
tcDataFamInstDecl mb_clsinfo
(L loc decl@(DataFamInstDecl
{ dfid_pats = pats
, dfid_tycon = fam_tc_name
, dfid_defn = defn@HsDataDefn { dd_ND = new_or_data, dd_cType = cType
, dd_ctxt = ctxt, dd_cons = cons } }))
= setSrcSpan loc $
tcAddDataFamInstCtxt decl $
do { fam_tc <- tcFamInstDeclCombined mb_clsinfo fam_tc_name
; checkTc (isFamilyTyCon fam_tc) (notFamily fam_tc)
; checkTc (isAlgTyCon fam_tc) (wrongKindOfFamily fam_tc)
; tcFamTyPats (unLoc fam_tc_name) (tyConKind fam_tc) pats
(kcDataDefn defn) $
\tvs' pats' res_kind -> do
{
checkValidFamPats fam_tc tvs' pats'
; checkConsistentFamInst mb_clsinfo fam_tc tvs' pats'
; checkTc (isLiftedTypeKind res_kind) $ tooFewParmsErr (tyConArity fam_tc)
; stupid_theta <- tcHsContext ctxt
; h98_syntax <- dataDeclChecks (tyConName fam_tc) new_or_data stupid_theta cons
; rep_tc_name <- newFamInstTyConName fam_tc_name pats'
; axiom_name <- newImplicitBinder rep_tc_name mkInstTyCoOcc
; let orig_res_ty = mkTyConApp fam_tc pats'
; (rep_tc, fam_inst) <- fixM $ \ ~(rec_rep_tc, _) ->
do { data_cons <- tcConDecls new_or_data rec_rep_tc
(tvs', orig_res_ty) cons
; tc_rhs <- case new_or_data of
DataType -> return (mkDataTyConRhs data_cons)
NewType -> ASSERT( not (null data_cons) )
mkNewTyConRhs rep_tc_name rec_rep_tc (head data_cons)
; let (eta_tvs, eta_pats) = eta_reduce tvs' pats'
axiom = mkSingleCoAxiom axiom_name eta_tvs fam_tc eta_pats
(mkTyConApp rep_tc (mkTyVarTys eta_tvs))
parent = FamInstTyCon axiom fam_tc pats'
roles = map (const Nominal) tvs'
rep_tc = buildAlgTyCon rep_tc_name tvs' roles cType stupid_theta tc_rhs
Recursive
False
h98_syntax parent
; fam_inst <- newFamInst (DataFamilyInst rep_tc) axiom
; return (rep_tc, fam_inst) }
; checkValidTyCon rep_tc
; return fam_inst } }
where
eta_reduce tvs pats = go (reverse tvs) (reverse pats)
go (tv:tvs) (pat:pats)
| Just tv' <- getTyVar_maybe pat
, tv == tv'
, not (tv `elemVarSet` tyVarsOfTypes pats)
= go tvs pats
go tvs pats = (reverse tvs, reverse pats)
\end{code}
Note [Eta reduction for data family axioms]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this
data family T a b :: *
newtype instance T Int a = MkT (IO a) deriving( Monad )
We'd like this to work. From the 'newtype instance' you might
think we'd get:
newtype TInt a = MkT (IO a)
axiom ax1 a :: T Int a ~ TInt a -- The type-instance part
axiom ax2 a :: TInt a ~ IO a -- The newtype part
But now what can we do? We have this problem
Given: d :: Monad IO
Wanted: d' :: Monad (T Int) = d |> ????
What coercion can we use for the ???
Solution: eta-reduce both axioms, thus:
axiom ax1 :: T Int ~ TInt
axiom ax2 :: TInt ~ IO
Now
d' = d |> Monad (sym (ax2 ; ax1))
This eta reduction happens both for data instances and newtype instances.
See Note [Newtype eta] in TyCon.
%************************************************************************
%* *
Type-checking instance declarations, pass 2
%* *
%************************************************************************
\begin{code}
tcInstDecls2 :: [LTyClDecl Name] -> [InstInfo Name]
-> TcM (LHsBinds Id)
tcInstDecls2 tycl_decls inst_decls
= do {
let class_decls = filter (isClassDecl . unLoc) tycl_decls
; dm_binds_s <- mapM tcClassDecl2 class_decls
; let dm_binds = unionManyBags dm_binds_s
; let dm_ids = collectHsBindsBinders dm_binds
; inst_binds_s <- tcExtendLetEnv TopLevel TopLevel dm_ids $
mapM tcInstDecl2 inst_decls
; return (dm_binds `unionBags` unionManyBags inst_binds_s) }
\end{code}
See Note [Default methods and instances]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The default method Ids are already in the type environment (see Note
[Default method Ids and Template Haskell] in TcTyClsDcls), BUT they
don't have their InlinePragmas yet. Usually that would not matter,
because the simplifier propagates information from binding site to
use. But, unusually, when compiling instance decls we *copy* the
INLINE pragma from the default method to the method for that
particular operation (see Note [INLINE and default methods] below).
So right here in tcInstDecls2 we must re-extend the type envt with
the default method Ids replete with their INLINE pragmas. Urk.
\begin{code}
tcInstDecl2 :: InstInfo Name -> TcM (LHsBinds Id)
tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = ibinds })
= recoverM (return emptyLHsBinds) $
setSrcSpan loc $
addErrCtxt (instDeclCtxt2 (idType dfun_id)) $
do {
; (inst_tyvars, dfun_theta, inst_head) <- tcSkolDFunType (idType dfun_id)
; let (clas, inst_tys) = tcSplitDFunHead inst_head
(class_tyvars, sc_theta, _, op_items) = classBigSig clas
sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys) sc_theta
; dfun_ev_vars <- newEvVars dfun_theta
; (sc_binds, sc_ev_vars) <- tcSuperClasses dfun_id inst_tyvars dfun_ev_vars sc_theta'
; spec_inst_info@(spec_inst_prags,_) <- tcSpecInstPrags dfun_id ibinds
; (meth_ids, meth_binds)
<- tcExtendTyVarEnv inst_tyvars $
tcInstanceMethods dfun_id clas inst_tyvars dfun_ev_vars
inst_tys spec_inst_info
op_items ibinds
; self_dict <- newDict clas inst_tys
; let class_tc = classTyCon clas
[dict_constr] = tyConDataCons class_tc
dict_bind = mkVarBind self_dict (L loc con_app_args)
con_app_tys = wrapId (mkWpTyApps inst_tys)
(dataConWrapId dict_constr)
con_app_scs = mkHsWrap (mkWpEvApps (map EvId sc_ev_vars)) con_app_tys
con_app_args = foldl app_to_meth con_app_scs meth_ids
app_to_meth :: HsExpr Id -> Id -> HsExpr Id
app_to_meth fun meth_id = L loc fun `HsApp` L loc (wrapId arg_wrapper meth_id)
inst_tv_tys = mkTyVarTys inst_tyvars
arg_wrapper = mkWpEvVarApps dfun_ev_vars <.> mkWpTyApps inst_tv_tys
(dfun_id_w_fun, dfun_spec_prags)
| isNewTyCon class_tc
= ( dfun_id `setInlinePragma` alwaysInlinePragma { inl_sat = Just 0 }
, SpecPrags [] )
| otherwise
= ( dfun_id `setIdUnfolding` mkDFunUnfolding (inst_tyvars ++ dfun_ev_vars)
dict_constr dfun_args
`setInlinePragma` dfunInlinePragma
, SpecPrags spec_inst_prags )
dfun_args :: [CoreExpr]
dfun_args = map Type inst_tys ++
map Var sc_ev_vars ++
map mk_meth_app meth_ids
mk_meth_app meth_id = Var meth_id `mkTyApps` inst_tv_tys `mkVarApps` dfun_ev_vars
export = ABE { abe_wrap = idHsWrapper, abe_poly = dfun_id_w_fun
, abe_mono = self_dict, abe_prags = dfun_spec_prags }
main_bind = AbsBinds { abs_tvs = inst_tyvars
, abs_ev_vars = dfun_ev_vars
, abs_exports = [export]
, abs_ev_binds = sc_binds
, abs_binds = unitBag (Generated, dict_bind) }
; return (unitBag (Generated, L loc main_bind) `unionBags`
listToBag meth_binds)
}
where
dfun_id = instanceDFunId ispec
loc = getSrcSpan dfun_id
tcSuperClasses :: DFunId -> [TcTyVar] -> [EvVar] -> TcThetaType
-> TcM (TcEvBinds, [EvVar])
tcSuperClasses dfun_id inst_tyvars dfun_ev_vars sc_theta
= do {
; (sc_binds, sc_evs) <- checkConstraints InstSkol inst_tyvars orig_ev_vars $
emitWanteds ScOrigin sc_theta
; if null inst_tyvars && null dfun_ev_vars
then return (sc_binds, sc_evs)
else return (emptyTcEvBinds, sc_lam_args) }
where
n_silent = dfunNSilent dfun_id
orig_ev_vars = drop n_silent dfun_ev_vars
sc_lam_args = map (find dfun_ev_vars) sc_theta
find [] pred
= pprPanic "tcInstDecl2" (ppr dfun_id $$ ppr (idType dfun_id) $$ ppr pred)
find (ev:evs) pred
| pred `eqPred` evVarPred ev = ev
| otherwise = find evs pred
mkMethIds :: HsSigFun -> Class -> [TcTyVar] -> [EvVar]
-> [TcType] -> Id -> TcM (TcId, TcSigInfo)
mkMethIds sig_fn clas tyvars dfun_ev_vars inst_tys sel_id
= do { let sel_occ = nameOccName sel_name
; meth_name <- newName (mkClassOpAuxOcc sel_occ)
; local_meth_name <- newName sel_occ
; local_meth_sig <- case lookupHsSig sig_fn sel_name of
Just hs_ty
-> do { sig_ty <- check_inst_sig hs_ty
; instTcTySig hs_ty sig_ty local_meth_name }
Nothing
-> do { loc <- getSrcSpanM
; instTcTySigFromId loc (mkLocalId local_meth_name local_meth_ty) }
; let meth_id = mkLocalId meth_name meth_ty
; return (meth_id, local_meth_sig) }
where
sel_name = idName sel_id
local_meth_ty = instantiateMethod clas sel_id inst_tys
meth_ty = mkForAllTys tyvars $ mkPiTypes dfun_ev_vars local_meth_ty
check_inst_sig hs_ty@(L loc _)
= setSrcSpan loc $
do { sig_ty <- tcHsSigType (FunSigCtxt sel_name) hs_ty
; inst_sigs <- xoptM Opt_InstanceSigs
; if inst_sigs then
unless (sig_ty `eqType` local_meth_ty)
(badInstSigErr sel_name local_meth_ty)
else
addErrTc (misplacedInstSig sel_name hs_ty)
; return sig_ty }
badInstSigErr :: Name -> Type -> TcM ()
badInstSigErr meth ty
= do { env0 <- tcInitTidyEnv
; let tidy_ty = tidyType env0 ty
; addErrTc (hang (ptext (sLit "Method signature does not match class; it should be"))
2 (pprPrefixName meth <+> dcolon <+> ppr tidy_ty)) }
misplacedInstSig :: Name -> LHsType Name -> SDoc
misplacedInstSig name hs_ty
= vcat [ hang (ptext (sLit "Illegal type signature in instance declaration:"))
2 (hang (pprPrefixName name)
2 (dcolon <+> ppr hs_ty))
, ptext (sLit "(Use InstanceSigs to allow this)") ]
tcSpecInstPrags :: DFunId -> InstBindings Name
-> TcM ([Located TcSpecPrag], PragFun)
tcSpecInstPrags dfun_id (InstBindings { ib_binds = binds, ib_pragmas = uprags })
= do { spec_inst_prags <- mapM (wrapLocM (tcSpecInst dfun_id)) $
filter isSpecInstLSig uprags
; return (spec_inst_prags, mkPragFun uprags binds) }
\end{code}
Note [Silent superclass arguments]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
See Trac #3731, #4809, #5751, #5913, #6117, which all
describe somewhat more complicated situations, but ones
encountered in practice.
THE PROBLEM
The problem is that it is all too easy to create a class whose
superclass is bottom when it should not be.
Consider the following (extreme) situation:
class C a => D a where ...
instance D [a] => D [a] where ...
Although this looks wrong (assume D [a] to prove D [a]), it is only a
more extreme case of what happens with recursive dictionaries, and it
can, just about, make sense because the methods do some work before
recursing.
To implement the dfun we must generate code for the superclass C [a],
which we had better not get by superclass selection from the supplied
argument:
dfun :: forall a. D [a] -> D [a]
dfun = \d::D [a] -> MkD (scsel d) ..
Otherwise if we later encounter a situation where
we have a [Wanted] dw::D [a] we might solve it thus:
dw := dfun dw
Which is all fine except that now ** the superclass C is bottom **!
THE SOLUTION
Our solution to this problem "silent superclass arguments". We pass
to each dfun some ``silent superclass arguments’’, which are the
immediate superclasses of the dictionary we are trying to
construct. In our example:
dfun :: forall a. C [a] -> D [a] -> D [a]
dfun = \(dc::C [a]) (dd::D [a]) -> DOrd dc ...
Notice the extra (dc :: C [a]) argument compared to the previous version.
This gives us:
-----------------------------------------------------------
DFun Superclass Invariant
~~~~~~~~~~~~~~~~~~~~~~~~
In the body of a DFun, every superclass argument to the
returned dictionary is
either * one of the arguments of the DFun,
or * constant, bound at top level
-----------------------------------------------------------
This net effect is that it is safe to treat a dfun application as
wrapping a dictionary constructor around its arguments (in particular,
a dfun never picks superclasses from the arguments under the
dictionary constructor). No superclass is hidden inside a dfun
application.
The extra arguments required to satisfy the DFun Superclass Invariant
always come first, and are called the "silent" arguments. You can
find out how many silent arguments there are using Id.dfunNSilent;
and then you can just drop that number of arguments to see the ones
that were in the original instance declaration.
DFun types are built (only) by MkId.mkDictFunId, so that is where we
decide what silent arguments are to be added.
In our example, if we had [Wanted] dw :: D [a] we would get via the instance:
dw := dfun d1 d2
[Wanted] (d1 :: C [a])
[Wanted] (d2 :: D [a])
And now, though we *can* solve:
d2 := dw
That's fine; and we solve d1:C[a] separately.
Test case SCLoop tests this fix.
Note [SPECIALISE instance pragmas]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
instance (Ix a, Ix b) => Ix (a,b) where
{-# SPECIALISE instance Ix (Int,Int) #-}
range (x,y) = ...
We make a specialised version of the dictionary function, AND
specialised versions of each *method*. Thus we should generate
something like this:
$dfIxPair :: (Ix a, Ix b) => Ix (a,b)
{-# DFUN [$crangePair, ...] #-}
{-# SPECIALISE $dfIxPair :: Ix (Int,Int) #-}
$dfIxPair da db = Ix ($crangePair da db) (...other methods...)
$crange :: (Ix a, Ix b) -> ((a,b),(a,b)) -> [(a,b)]
{-# SPECIALISE $crange :: ((Int,Int),(Int,Int)) -> [(Int,Int)] #-}
$crange da db =
The SPECIALISE pragmas are acted upon by the desugarer, which generate
dii :: Ix Int
dii = ...
$s$dfIxPair :: Ix ((Int,Int),(Int,Int))
{-# DFUN [$crangePair di di, ...] #-}
$s$dfIxPair = Ix ($crangePair di di) (...)
{-# RULE forall (d1,d2:Ix Int). $dfIxPair Int Int d1 d2 = $s$dfIxPair #-}
$s$crangePair :: ((Int,Int),(Int,Int)) -> [(Int,Int)]
$c$crangePair = ...specialised RHS of $crangePair...
{-# RULE forall (d1,d2:Ix Int). $crangePair Int Int d1 d2 = $s$crangePair #-}
Note that
* The specialised dictionary $s$dfIxPair is very much needed, in case we
call a function that takes a dictionary, but in a context where the
specialised dictionary can be used. See Trac #7797.
* The ClassOp rule for 'range' works equally well on $s$dfIxPair, because
it still has a DFunUnfolding. See Note [ClassOp/DFun selection]
* A call (range ($dfIxPair Int Int d1 d2)) might simplify two ways:
--> {ClassOp rule for range} $crangePair Int Int d1 d2
--> {SPEC rule for $crangePair} $s$crangePair
or thus:
--> {SPEC rule for $dfIxPair} range $s$dfIxPair
--> {ClassOpRule for range} $s$crangePair
It doesn't matter which way.
* We want to specialise the RHS of both $dfIxPair and $crangePair,
but the SAME HsWrapper will do for both! We can call tcSpecPrag
just once, and pass the result (in spec_inst_info) to tcInstanceMethods.
\begin{code}
tcSpecInst :: Id -> Sig Name -> TcM TcSpecPrag
tcSpecInst dfun_id prag@(SpecInstSig hs_ty)
= addErrCtxt (spec_ctxt prag) $
do { let name = idName dfun_id
; (tyvars, theta, clas, tys) <- tcHsInstHead SpecInstCtxt hs_ty
; let (_, spec_dfun_ty) = mkDictFunTy tyvars theta clas tys
; co_fn <- tcSubType (SpecPragOrigin name) SpecInstCtxt
(idType dfun_id) spec_dfun_ty
; return (SpecPrag dfun_id co_fn defaultInlinePragma) }
where
spec_ctxt prag = hang (ptext (sLit "In the SPECIALISE pragma")) 2 (ppr prag)
tcSpecInst _ _ = panic "tcSpecInst"
\end{code}
%************************************************************************
%* *
Type-checking an instance method
%* *
%************************************************************************
tcInstanceMethod
- Make the method bindings, as a [(NonRec, HsBinds)], one per method
- Remembering to use fresh Name (the instance method Name) as the binder
- Bring the instance method Ids into scope, for the benefit of tcInstSig
- Use sig_fn mapping instance method Name -> instance tyvars
- Ditto prag_fn
- Use tcValBinds to do the checking
\begin{code}
tcInstanceMethods :: DFunId -> Class -> [TcTyVar]
-> [EvVar]
-> [TcType]
-> ([Located TcSpecPrag], PragFun)
-> [(Id, DefMeth)]
-> InstBindings Name
-> TcM ([Id], [(Origin, LHsBind Id)])
tcInstanceMethods dfun_id clas tyvars dfun_ev_vars inst_tys
(spec_inst_prags, prag_fn)
op_items (InstBindings { ib_binds = binds
, ib_pragmas = sigs
, ib_standalone_deriving
= standalone_deriv })
= do { traceTc "tcInstMeth" (ppr sigs $$ ppr binds)
; let hs_sig_fn = mkHsSigFun sigs
; checkMinimalDefinition
; mapAndUnzipM (tc_item hs_sig_fn) op_items }
where
tc_item :: HsSigFun -> (Id, DefMeth) -> TcM (Id, (Origin, LHsBind Id))
tc_item sig_fn (sel_id, dm_info)
= case findMethodBind (idName sel_id) binds of
Just (user_bind, bndr_loc)
-> tc_body sig_fn sel_id standalone_deriv user_bind bndr_loc
Nothing -> do { traceTc "tc_def" (ppr sel_id)
; tc_default sig_fn sel_id dm_info }
tc_body :: HsSigFun -> Id -> Bool -> (Origin, LHsBind Name)
-> SrcSpan -> TcM (TcId, (Origin, LHsBind Id))
tc_body sig_fn sel_id generated_code rn_bind bndr_loc
= add_meth_ctxt sel_id generated_code (snd rn_bind) $
do { traceTc "tc_item" (ppr sel_id <+> ppr (idType sel_id))
; (meth_id, local_meth_sig) <- setSrcSpan bndr_loc $
mkMethIds sig_fn clas tyvars dfun_ev_vars
inst_tys sel_id
; let prags = prag_fn (idName sel_id)
; meth_id1 <- addInlinePrags meth_id prags
; spec_prags <- tcSpecPrags meth_id1 prags
; bind <- tcInstanceMethodBody InstSkol
tyvars dfun_ev_vars
meth_id1 local_meth_sig
(mk_meth_spec_prags meth_id1 spec_prags)
rn_bind
; return (meth_id1, bind) }
tc_default :: HsSigFun -> Id -> DefMeth -> TcM (TcId, (Origin, LHsBind Id))
tc_default sig_fn sel_id (GenDefMeth dm_name)
= do { meth_bind <- mkGenericDefMethBind clas inst_tys sel_id dm_name
; tc_body sig_fn sel_id False
(Generated, meth_bind) inst_loc }
tc_default sig_fn sel_id NoDefMeth
= do { traceTc "tc_def: warn" (ppr sel_id)
; (meth_id, _) <- mkMethIds sig_fn clas tyvars dfun_ev_vars
inst_tys sel_id
; dflags <- getDynFlags
; return (meth_id,
(Generated, mkVarBind meth_id $
mkLHsWrap lam_wrapper (error_rhs dflags))) }
where
error_rhs dflags = L inst_loc $ HsApp error_fun (error_msg dflags)
error_fun = L inst_loc $ wrapId (WpTyApp meth_tau) nO_METHOD_BINDING_ERROR_ID
error_msg dflags = L inst_loc (HsLit (HsStringPrim (unsafeMkByteString (error_string dflags))))
meth_tau = funResultTy (applyTys (idType sel_id) inst_tys)
error_string dflags = showSDoc dflags (hcat [ppr inst_loc, text "|", ppr sel_id ])
lam_wrapper = mkWpTyLams tyvars <.> mkWpLams dfun_ev_vars
tc_default sig_fn sel_id (DefMeth dm_name)
= do {
; self_dict <- newDict clas inst_tys
; let self_ev_bind = EvBind self_dict
(EvDFunApp dfun_id (mkTyVarTys tyvars) (map EvId dfun_ev_vars))
; (meth_id, local_meth_sig) <- mkMethIds sig_fn clas tyvars dfun_ev_vars
inst_tys sel_id
; dm_id <- tcLookupId dm_name
; let dm_inline_prag = idInlinePragma dm_id
rhs = HsWrap (mkWpEvVarApps [self_dict] <.> mkWpTyApps inst_tys) $
HsVar dm_id
local_meth_id = sig_id local_meth_sig
meth_bind = mkVarBind local_meth_id (L inst_loc rhs)
meth_id1 = meth_id `setInlinePragma` dm_inline_prag
export = ABE { abe_wrap = idHsWrapper, abe_poly = meth_id1
, abe_mono = local_meth_id
, abe_prags = mk_meth_spec_prags meth_id1 [] }
bind = AbsBinds { abs_tvs = tyvars, abs_ev_vars = dfun_ev_vars
, abs_exports = [export]
, abs_ev_binds = EvBinds (unitBag self_ev_bind)
, abs_binds = unitBag (Generated, meth_bind) }
; return (meth_id1, (Generated, L inst_loc bind)) }
mk_meth_spec_prags :: Id -> [LTcSpecPrag] -> TcSpecPrags
mk_meth_spec_prags meth_id spec_prags_for_me
= SpecPrags (spec_prags_for_me ++ spec_prags_from_inst)
where
spec_prags_from_inst
| isInlinePragma (idInlinePragma meth_id)
= []
| otherwise
= [ L inst_loc (SpecPrag meth_id wrap inl)
| L inst_loc (SpecPrag _ wrap inl) <- spec_inst_prags]
inst_loc = getSrcSpan dfun_id
add_meth_ctxt sel_id generated_code rn_bind thing
| generated_code = addLandmarkErrCtxt (derivBindCtxt sel_id clas inst_tys rn_bind) thing
| otherwise = thing
checkMinimalDefinition
= whenIsJust (isUnsatisfied methodExists (classMinimalDef clas)) $
warnUnsatisifiedMinimalDefinition
where
methodExists meth = isJust (findMethodBind meth binds)
mkGenericDefMethBind :: Class -> [Type] -> Id -> Name -> TcM (LHsBind Name)
mkGenericDefMethBind clas inst_tys sel_id dm_name
=
do { dflags <- getDynFlags
; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
(vcat [ppr clas <+> ppr inst_tys,
nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
; return (noLoc $ mkTopFunBind (noLoc (idName sel_id))
[mkSimpleMatch [] rhs]) }
where
rhs = nlHsVar dm_name
wrapId :: HsWrapper -> id -> HsExpr id
wrapId wrapper id = mkHsWrap wrapper (HsVar id)
derivBindCtxt :: Id -> Class -> [Type ] -> LHsBind Name -> SDoc
derivBindCtxt sel_id clas tys _bind
= vcat [ ptext (sLit "When typechecking the code for ") <+> quotes (ppr sel_id)
, nest 2 (ptext (sLit "in a standalone derived instance for")
<+> quotes (pprClassPred clas tys) <> colon)
, nest 2 $ ptext (sLit "To see the code I am typechecking, use -ddump-deriv") ]
warnMissingMethodOrAT :: String -> Name -> TcM ()
warnMissingMethodOrAT what name
= do { warn <- woptM Opt_WarnMissingMethods
; traceTc "warn" (ppr name <+> ppr warn <+> ppr (not (startsWithUnderscore (getOccName name))))
; warnTc (warn
&& not (startsWithUnderscore (getOccName name)))
(ptext (sLit "No explicit") <+> text what <+> ptext (sLit "or default declaration for")
<+> quotes (ppr name)) }
warnUnsatisifiedMinimalDefinition :: ClassMinimalDef -> TcM ()
warnUnsatisifiedMinimalDefinition mindef
= do { warn <- woptM Opt_WarnMissingMethods
; warnTc warn message
}
where
message = vcat [ptext (sLit "No explicit implementation for")
,nest 2 $ pprBooleanFormulaNice mindef
]
\end{code}
Note [Export helper functions]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We arrange to export the "helper functions" of an instance declaration,
so that they are not subject to preInlineUnconditionally, even if their
RHS is trivial. Reason: they are mentioned in the DFunUnfolding of
the dict fun as Ids, not as CoreExprs, so we can't substitute a
non-variable for them.
We could change this by making DFunUnfoldings have CoreExprs, but it
seems a bit simpler this way.
Note [Default methods in instances]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this
class Baz v x where
foo :: x -> x
foo y =
instance Baz Int Int
From the class decl we get
$dmfoo :: forall v x. Baz v x => x -> x
$dmfoo y =
Notice that the type is ambiguous. That's fine, though. The instance
decl generates
$dBazIntInt = MkBaz fooIntInt
fooIntInt = $dmfoo Int Int $dBazIntInt
BUT this does mean we must generate the dictionary translation of
fooIntInt directly, rather than generating source-code and
type-checking it. That was the bug in Trac #1061. In any case it's
less work to generate the translated version!
Note [INLINE and default methods]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Default methods need special case. They are supposed to behave rather like
macros. For exmample
class Foo a where
op1, op2 :: Bool -> a -> a
{-# INLINE op1 #-}
op1 b x = op2 (not b) x
instance Foo Int where
-- op1 via default method
op2 b x =
The instance declaration should behave
just as if 'op1' had been defined with the
code, and INLINE pragma, from its original
definition.
That is, just as if you'd written
instance Foo Int where
op2 b x =
{-# INLINE op1 #-}
op1 b x = op2 (not b) x
So for the above example we generate:
{-# INLINE $dmop1 #-}
-- $dmop1 has an InlineCompulsory unfolding
$dmop1 d b x = op2 d (not b) x
$fFooInt = MkD $cop1 $cop2
{-# INLINE $cop1 #-}
$cop1 = $dmop1 $fFooInt
$cop2 =
Note carefullly:
* We *copy* any INLINE pragma from the default method $dmop1 to the
instance $cop1. Otherwise we'll just inline the former in the
latter and stop, which isn't what the user expected
* Regardless of its pragma, we give the default method an
unfolding with an InlineCompulsory source. That means
that it'll be inlined at every use site, notably in
each instance declaration, such as $cop1. This inlining
must happen even though
a) $dmop1 is not saturated in $cop1
b) $cop1 itself has an INLINE pragma
It's vital that $dmop1 *is* inlined in this way, to allow the mutual
recursion between $fooInt and $cop1 to be broken
* To communicate the need for an InlineCompulsory to the desugarer
(which makes the Unfoldings), we use the IsDefaultMethod constructor
in TcSpecPrags.
%************************************************************************
%* *
\subsection{Error messages}
%* *
%************************************************************************
\begin{code}
instDeclCtxt1 :: LHsType Name -> SDoc
instDeclCtxt1 hs_inst_ty
= inst_decl_ctxt (case unLoc hs_inst_ty of
HsForAllTy _ _ _ (L _ ty') -> ppr ty'
_ -> ppr hs_inst_ty)
instDeclCtxt2 :: Type -> SDoc
instDeclCtxt2 dfun_ty
= inst_decl_ctxt (ppr (mkClassPred cls tys))
where
(_,_,cls,tys) = tcSplitDFunTy dfun_ty
inst_decl_ctxt :: SDoc -> SDoc
inst_decl_ctxt doc = hang (ptext (sLit "In the instance declaration for"))
2 (quotes doc)
badBootFamInstDeclErr :: SDoc
badBootFamInstDeclErr
= ptext (sLit "Illegal family instance in hs-boot file")
notFamily :: TyCon -> SDoc
notFamily tycon
= vcat [ ptext (sLit "Illegal family instance for") <+> quotes (ppr tycon)
, nest 2 $ parens (ppr tycon <+> ptext (sLit "is not an indexed type family"))]
tooFewParmsErr :: Arity -> SDoc
tooFewParmsErr arity
= ptext (sLit "Family instance has too few parameters; expected") <+>
ppr arity
assocInClassErr :: Located Name -> SDoc
assocInClassErr name
= ptext (sLit "Associated type") <+> quotes (ppr name) <+>
ptext (sLit "must be inside a class instance")
badFamInstDecl :: Located Name -> SDoc
badFamInstDecl tc_name
= vcat [ ptext (sLit "Illegal family instance for") <+>
quotes (ppr tc_name)
, nest 2 (parens $ ptext (sLit "Use TypeFamilies to allow indexed type families")) ]
notOpenFamily :: TyCon -> SDoc
notOpenFamily tc
= ptext (sLit "Illegal instance for closed family") <+> quotes (ppr tc)
\end{code}