X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcTyClsDecls.lhs;h=18be4c37f0290d4186663951cfc5a1db112d230f;hp=2d68a6e3b8083e528a7a24a180a7f73824a556a9;hb=9ffadf219cbc4f8ec57264786df936a3cee88aec;hpb=24a5fdb5fe20290cbb9b58b2901e8d2fd651d3f3 diff --git a/compiler/typecheck/TcTyClsDecls.lhs b/compiler/typecheck/TcTyClsDecls.lhs index 2d68a6e..18be4c3 100644 --- a/compiler/typecheck/TcTyClsDecls.lhs +++ b/compiler/typecheck/TcTyClsDecls.lhs @@ -7,7 +7,7 @@ TcTyClsDecls: Typecheck type and class declarations \begin{code} module TcTyClsDecls ( - tcTyAndClassDecls, tcFamInstDecl + tcTyAndClassDecls, tcFamInstDecl, mkAuxBinds ) where #include "HsVersions.h" @@ -25,6 +25,7 @@ import TcClassDcl import TcHsType import TcMType import TcType +import TysWiredIn ( unitTy ) import FunDeps import Type import Generics @@ -32,6 +33,8 @@ import Class import TyCon import DataCon import Id +import MkId ( rEC_SEL_ERROR_ID ) +import IdInfo import Var import VarSet import Name @@ -46,7 +49,10 @@ import ListSetOps import Digraph import DynFlags import FastString +import Unique ( mkBuiltinUnique ) +import BasicTypes +import Bag import Data.List import Control.Monad ( mplus ) \end{code} @@ -133,8 +139,9 @@ indeed type families). I think. \begin{code} tcTyAndClassDecls :: ModDetails -> [LTyClDecl Name] - -> TcM TcGblEnv -- Input env extended by types and classes - -- and their implicit Ids,DataCons + -> TcM (TcGblEnv, -- Input env extended by types and classes + -- and their implicit Ids,DataCons + HsValBinds Name) -- Renamed bindings for record selectors -- Fails if there are any errors tcTyAndClassDecls boot_details allDecls @@ -199,11 +206,13 @@ tcTyAndClassDecls boot_details allDecls -- NB: All associated types and their implicit things will be added a -- second time here. This doesn't matter as the definitions are -- the same. - ; let { implicit_things = concatMap implicitTyThings alg_tyclss } + ; let { implicit_things = concatMap implicitTyThings alg_tyclss + ; aux_binds = mkAuxBinds alg_tyclss } ; traceTc ((text "Adding" <+> ppr alg_tyclss) $$ (text "and" <+> ppr implicit_things)) - ; tcExtendGlobalEnv implicit_things getGblEnv - }} + ; env <- tcExtendGlobalEnv implicit_things getGblEnv + ; return (env, aux_binds) } + } where -- Pull associated types out of class declarations, to tie them into the -- knot above. @@ -230,7 +239,7 @@ mkGlobalThings decls things %************************************************************************ %* * -\subsection{Type checking family instances} + Type checking family instances %* * %************************************************************************ @@ -360,7 +369,7 @@ tcFamInstDecl1 d = pprPanic "tcFamInstDecl1" (ppr d) -- * Here we check that a type instance matches its kind signature, but we do -- not check whether there is a pattern for each type index; the latter -- check is only required for type synonym instances. --- + kcIdxTyPats :: TyClDecl Name -> ([LHsTyVarBndr Name] -> [LHsType Name] -> Kind -> TyCon -> TcM a) -- ^^kinded tvs ^^kinded ty pats ^^res kind @@ -853,8 +862,9 @@ tcConDecl unbox_strict existential_ok rep_tycon res_tmpl -- Data types -- In this case orig_res_ty = T (e,e) tcResultType :: ([TyVar], Type) -- Template for result type; e.g. - -- data T a b c = ... gives ([a,b,c], T a b) - -> [TyVar] -- where MkT :: forall a b c. ... + -- data instance T [a] b c = ... + -- gives template ([a,b,c], T [a] b c) + -> [TyVar] -- where MkT :: forall x y z. ... -> ResType Name -> TcM ([TyVar], -- Universal [TyVar], -- Existential (distinct OccNames from univs) @@ -879,6 +889,7 @@ tcResultType (tmpl_tvs, res_tmpl) dc_tvs (ResTyGADT res_ty) -- b b~z -- z -- Existentials are the leftover type vars: [x,y] + -- So we return ([a,b,z], [x,y], [a~(x,y),b~z], T [(x,y)] z z) = do { res_ty' <- tcHsKindedType res_ty ; let Just subst = tcMatchTy (mkVarSet tmpl_tvs) res_tmpl res_ty' @@ -952,9 +963,10 @@ But it's the *argument* type that matters. This is fine: data S = MkS S !Int because Int is non-recursive. + %************************************************************************ %* * -\subsection{Dependency analysis} + Validity checking %* * %************************************************************************ @@ -1175,9 +1187,175 @@ checkValidClass cls -- forall has an (Eq a) constraint. Whereas in general, each constraint -- in the context of a for-all must mention at least one quantified -- type variable. What a mess! +\end{code} + + +%************************************************************************ +%* * + Building record selectors +%* * +%************************************************************************ + +\begin{code} +mkAuxBinds :: [TyThing] -> HsValBinds Name +mkAuxBinds ty_things + = ValBindsOut [(NonRecursive, b) | b <- binds] sigs + where + (sigs, binds) = unzip rec_sels + rec_sels = map mkRecSelBind [ (tc,fld) + | ATyCon tc <- ty_things + , fld <- tyConFields tc ] ---------------------------------------------------------------------- +mkRecSelBind :: (TyCon, FieldLabel) -> (LSig Name, LHsBinds Name) +mkRecSelBind (tycon, sel_name) + = (L loc (IdSig sel_id), unitBag (L loc sel_bind)) + where + loc = getSrcSpan tycon + sel_id = Var.mkLocalVar rec_details sel_name sel_ty vanillaIdInfo + rec_details = RecSelId { sel_tycon = tycon, sel_naughty = is_naughty } + + -- Find a representative constructor, con1 + all_cons = tyConDataCons tycon + cons_w_field = [ con | con <- all_cons + , sel_name `elem` dataConFieldLabels con ] + con1 = ASSERT( not (null cons_w_field) ) head cons_w_field + + -- Selector type; Note [Polymorphic selectors] + field_ty = dataConFieldType con1 sel_name + (field_tvs, field_theta, field_tau) + | is_naughty = ([], [], unitTy) + | otherwise = tcSplitSigmaTy field_ty + data_ty = dataConOrigResTy con1 + data_tvs = tyVarsOfType data_ty + is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tvs) + sel_ty = mkForAllTys (varSetElems data_tvs ++ field_tvs) $ + mkPhiTy (dataConStupidTheta con1) $ -- Urgh! + mkPhiTy field_theta $ -- Urgh! + mkFunTy data_ty field_tau + + -- Make the binding: sel (C2 { fld = x }) = x + -- sel (C7 { fld = x }) = x + -- where cons_w_field = [C2,C7] + sel_bind = mkFunBind sel_lname (map mk_match cons_w_field ++ deflt) + mk_match con = mkSimpleMatch [L loc (mk_sel_pat con)] + (L loc match_body) + mk_sel_pat con = ConPatIn (L loc (getName con)) (RecCon rec_fields) + rec_fields = HsRecFields { rec_flds = [rec_field], rec_dotdot = Nothing } + rec_field = HsRecField { hsRecFieldId = sel_lname + , hsRecFieldArg = nlVarPat field_var + , hsRecPun = False } + match_body | is_naughty = ExplicitTuple [] Boxed + | otherwise = HsVar field_var + sel_lname = L loc sel_name + field_var = mkInternalName (mkBuiltinUnique 1) (getOccName sel_name) loc + + -- Add catch-all default case unless the case is exhaustive + -- We do this explicitly so that we get a nice error message that + -- mentions this particular record selector + deflt | length cons_w_field == length all_cons = [] + | otherwise = [mkSimpleMatch [nlWildPat] + (nlHsApp (nlHsVar (getName rEC_SEL_ERROR_ID)) + (nlHsLit msg_lit))] + msg_lit = HsStringPrim $ mkFastString $ + occNameString (getOccName sel_name) + +--------------- +tyConFields :: TyCon -> [FieldLabel] +tyConFields tc + | isAlgTyCon tc = nub (concatMap dataConFieldLabels (tyConDataCons tc)) + | otherwise = [] +\end{code} + +Note [Polymorphic selectors] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +When a record has a polymorphic field, we pull the foralls out to the front. + data T = MkT { f :: forall a. [a] -> a } +Then f :: forall a. T -> [a] -> a +NOT f :: T -> forall a. [a] -> a + +This is horrid. It's only needed in deeply obscure cases, which I hate. +The only case I know is test tc163, which is worth looking at. It's far +from clear that this test should succeed at all! + +Note [Naughty record selectors] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +A "naughty" field is one for which we can't define a record +selector, because an existential type variable would escape. For example: + data T = forall a. MkT { x,y::a } +We obviously can't define + x (MkT v _) = v +Nevertheless we *do* put a RecSelId into the type environment +so that if the user tries to use 'x' as a selector we can bleat +helpfully, rather than saying unhelpfully that 'x' is not in scope. +Hence the sel_naughty flag, to identify record selectors that don't really exist. + +In general, a field is naughty if its type mentions a type variable that +isn't in the result type of the constructor. + +We make a dummy binding for naughty selectors, so that they can be treated +uniformly, apart from their sel_naughty field. The function is never called. + +Note [GADT record selectors] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +For GADTs, we require that all constructors with a common field 'f' have the same +result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon] +E.g. + data T where + T1 { f :: Maybe a } :: T [a] + T2 { f :: Maybe a, y :: b } :: T [a] + +and now the selector takes that result type as its argument: + f :: forall a. T [a] -> Maybe a + +Details: the "real" types of T1,T2 are: + T1 :: forall r a. (r~[a]) => a -> T r + T2 :: forall r a b. (r~[a]) => a -> b -> T r + +So the selector loooks like this: + f :: forall a. T [a] -> Maybe a + f (a:*) (t:T [a]) + = case t of + T1 c (g:[a]~[c]) (v:Maybe c) -> v `cast` Maybe (right (sym g)) + T2 c d (g:[a]~[c]) (v:Maybe c) (w:d) -> v `cast` Maybe (right (sym g)) + +Note the forall'd tyvars of the selector are just the free tyvars +of the result type; there may be other tyvars in the constructor's +type (e.g. 'b' in T2). + +Note the need for casts in the result! + +Note [Selector running example] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +It's OK to combine GADTs and type families. Here's a running example: + + data instance T [a] where + T1 { fld :: b } :: T [Maybe b] + +The representation type looks like this + data :R7T a where + T1 { fld :: b } :: :R7T (Maybe b) + +and there's coercion from the family type to the representation type + :CoR7T a :: T [a] ~ :R7T a + +The selector we want for fld looks like this: + + fld :: forall b. T [Maybe b] -> b + fld = /\b. \(d::T [Maybe b]). + case d `cast` :CoR7T (Maybe b) of + T1 (x::b) -> x + +The scrutinee of the case has type :R7T (Maybe b), which can be +gotten by appying the eq_spec to the univ_tvs of the data con. + +%************************************************************************ +%* * + Error messages +%* * +%************************************************************************ + +\begin{code} resultTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc resultTypeMisMatch field_name con1 con2 = vcat [sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2, @@ -1313,13 +1491,6 @@ badFamInstDecl tc_name quotes (ppr tc_name) , nest 2 (parens $ ptext (sLit "Use -XTypeFamilies to allow indexed type families")) ] -{- -badGadtIdxTyDecl :: Name -> SDoc -badGadtIdxTyDecl tc_name - = vcat [ ptext (sLit "Illegal generalised algebraic data declaration for") <+> - quotes (ppr tc_name) - , nest 2 (parens $ ptext (sLit "Family instances can not yet use GADT declarations")) ] --} tooManyParmsErr :: Located Name -> SDoc tooManyParmsErr tc_name = ptext (sLit "Family instance has too many parameters:") <+>