-- 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/CodingStyle#Warnings
+-- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
-- for details
module TcUnify (
unifyType, unifyTypeList, unifyTheta,
unifyKind, unifyKinds, unifyFunKind,
checkExpectedKind,
- preSubType, boxyMatchTypes,
+ preSubType, boxyMatchTypes,
--------------------------------
-- Holes
tcInfer, subFunTys, unBox, refineBox, refineBoxToTau, withBox,
boxyUnify, boxyUnifyList, zapToMonotype,
- boxySplitListTy, boxySplitTyConApp, boxySplitAppTy,
+ boxySplitListTy, boxySplitPArrTy, boxySplitTyConApp, boxySplitAppTy,
wrapFunResCoercion
) where
----------------------
boxySplitTyConApp :: TyCon -- T :: k1 -> ... -> kn -> *
-> BoxyRhoType -- Expected type (T a b c)
- -> TcM [BoxySigmaType] -- Element types, a b c
- -- It's used for wired-in tycons, so we call checkWiredInTyCOn
+ -> TcM ([BoxySigmaType], -- Element types, a b c
+ CoercionI)
+ -- It's used for wired-in tycons, so we call checkWiredInTyCon
-- Precondition: never called with FunTyCon
-- Precondition: input type :: *
loop n_req args_so_far ty
| Just ty' <- tcView ty = loop n_req args_so_far ty'
- loop n_req args_so_far (TyConApp tycon args)
+ loop n_req args_so_far ty@(TyConApp tycon args)
| tc == tycon
= ASSERT( n_req == length args) -- ty::*
- return (args ++ args_so_far)
+ return (args ++ args_so_far, IdCo)
+
+ | isOpenSynTyCon tycon -- try to normalise type family application
+ = do { (coi1, ty') <- tcNormaliseFamInst ty
+ ; case coi1 of
+ IdCo -> defer -- no progress, but maybe solvable => defer
+ ACo _ -> -- progress: so lets try again
+ do { (args, coi2) <- loop n_req args_so_far ty'
+ ; return $ (args, coi2 `mkTransCoI` mkSymCoI coi1)
+ }
+ }
loop n_req args_so_far (AppTy fun arg)
| n_req > 0
- = loop (n_req - 1) (arg:args_so_far) fun
+ = do { (args, coi) <- loop (n_req - 1) (arg:args_so_far) fun
+ ; return (args, mkAppTyCoI fun coi arg IdCo)
+ }
loop n_req args_so_far (TyVarTy tv)
| isTyConableTyVar tv
; case cts of
Indirect ty -> loop n_req args_so_far ty
Flexi -> do { arg_tys <- withMetaTvs tv arg_kinds mk_res_ty
- ; return (arg_tys ++ args_so_far) }
- }
+ ; return (arg_tys ++ args_so_far, IdCo) }
+ }
+ | otherwise -- defer as tyvar may be refined by equalities
+ = defer
where
- mk_res_ty arg_tys' = mkTyConApp tc arg_tys'
(arg_kinds, res_kind) = splitKindFunTysN n_req (tyConKind tc)
- loop _ _ _ = boxySplitFailure (mkTyConApp tc (mkTyVarTys (tyConTyVars tc))) orig_ty
+ loop _ _ _ = boxySplitFailure (mkTyConApp tc (mkTyVarTys (tyConTyVars tc)))
+ orig_ty
+
+ -- defer splitting by generating an equality constraint
+ defer = boxySplitDefer arg_kinds mk_res_ty orig_ty
+ where
+ (arg_kinds, _) = splitKindFunTys (tyConKind tc)
+
+ -- apply splitted tycon to arguments
+ mk_res_ty = mkTyConApp tc
----------------------
-boxySplitListTy :: BoxyRhoType -> TcM BoxySigmaType -- Special case for lists
-boxySplitListTy exp_ty = do { [elt_ty] <- boxySplitTyConApp listTyCon exp_ty
- ; return elt_ty }
+boxySplitListTy :: BoxyRhoType -> TcM (BoxySigmaType, CoercionI)
+-- Special case for lists
+boxySplitListTy exp_ty
+ = do { ([elt_ty], coi) <- boxySplitTyConApp listTyCon exp_ty
+ ; return (elt_ty, coi) }
+----------------------
+boxySplitPArrTy :: BoxyRhoType -> TcM (BoxySigmaType, CoercionI)
+-- Special case for parrs
+boxySplitPArrTy exp_ty
+ = do { ([elt_ty], coi) <- boxySplitTyConApp parrTyCon exp_ty
+ ; return (elt_ty, coi) }
----------------------
boxySplitAppTy :: BoxyRhoType -- Type to split: m a
- -> TcM (BoxySigmaType, BoxySigmaType) -- Returns m, a
+ -> TcM ((BoxySigmaType, BoxySigmaType), -- Returns m, a
+ CoercionI)
-- If the incoming type is a mutable type variable of kind k, then
-- boxySplitAppTy returns a new type variable (m: * -> k); note the *.
-- If the incoming type is boxy, then so are the result types; and vice versa
loop ty
| Just (fun_ty, arg_ty) <- tcSplitAppTy_maybe ty
- = return (fun_ty, arg_ty)
+ = return ((fun_ty, arg_ty), IdCo)
+
+ loop ty@(TyConApp tycon args)
+ | isOpenSynTyCon tycon -- try to normalise type family application
+ = do { (coi1, ty') <- tcNormaliseFamInst ty
+ ; case coi1 of
+ IdCo -> defer -- no progress, but maybe solvable => defer
+ ACo co -> -- progress: so lets try again
+ do { (args, coi2) <- loop ty'
+ ; return $ (args, coi2 `mkTransCoI` mkSymCoI coi1)
+ }
+ }
loop (TyVarTy tv)
| isTyConableTyVar tv
= do { cts <- readMetaTyVar tv
; case cts of
Indirect ty -> loop ty
- Flexi -> do { [fun_ty,arg_ty] <- withMetaTvs tv kinds mk_res_ty
- ; return (fun_ty, arg_ty) } }
+ Flexi -> do { [fun_ty, arg_ty] <- withMetaTvs tv kinds mk_res_ty
+ ; return ((fun_ty, arg_ty), IdCo) } }
+ | otherwise -- defer as tyvar may be refined by equalities
+ = defer
where
- mk_res_ty [fun_ty', arg_ty'] = mkAppTy fun_ty' arg_ty'
- mk_res_ty other = panic "TcUnify.mk_res_ty2"
tv_kind = tyVarKind tv
kinds = [mkArrowKind liftedTypeKind (defaultKind tv_kind),
-- m :: * -> k
loop _ = boxySplitFailure (mkAppTy alphaTy betaTy) orig_ty
+ -- defer splitting by generating an equality constraint
+ defer = do { ([ty1, ty2], coi) <- boxySplitDefer arg_kinds mk_res_ty orig_ty
+ ; return ((ty1, ty2), coi)
+ }
+ where
+ orig_kind = typeKind orig_ty
+ arg_kinds = [mkArrowKind liftedTypeKind (defaultKind orig_kind),
+ -- m :: * -> k
+ liftedTypeKind] -- arg type :: *
+
+ -- build type application
+ mk_res_ty [fun_ty', arg_ty'] = mkAppTy fun_ty' arg_ty'
+ mk_res_ty _other = panic "TcUnify.mk_res_ty2"
+
------------------
boxySplitFailure actual_ty expected_ty
= unifyMisMatch False False actual_ty expected_ty
-- "outer" is False, so we don't pop the context
-- which is what we want since we have not pushed one!
+
+------------------
+boxySplitDefer :: [Kind] -- kinds of required arguments
+ -> ([TcType] -> TcTauType) -- construct lhs from argument tyvars
+ -> BoxyRhoType -- type to split
+ -> TcM ([TcType], CoercionI)
+boxySplitDefer kinds mkTy orig_ty
+ = do { tau_tys <- mapM newFlexiTyVarTy kinds
+ ; coi <- defer_unification False False (mkTy tau_tys) orig_ty
+ ; return (tau_tys, coi)
+ }
\end{code}
; let
-- The WpLet binds any Insts which came out of the simplification.
- dict_ids = map instToId dicts
- co_fn = mkWpTyLams tvs' <.> mkWpLams dict_ids <.> WpLet inst_binds
+ dict_vars = map instToVar dicts
+ co_fn = mkWpTyLams tvs' <.> mkWpLams dict_vars <.> WpLet inst_binds
; returnM (co_fn, result) }
where
free_tvs = tyVarsOfType expected_ty `unionVarSet` extra_tvs
-- need to defer unification by generating a wanted equality constraint.
go1 outer ty1 ty2
| ty1_is_fun || ty2_is_fun
- = do { (coi1, ty1') <- if ty1_is_fun then tcNormalizeFamInst ty1
+ = do { (coi1, ty1') <- if ty1_is_fun then tcNormaliseFamInst ty1
else return (IdCo, ty1)
- ; (coi2, ty2') <- if ty2_is_fun then tcNormalizeFamInst ty2
+ ; (coi2, ty2') <- if ty2_is_fun then tcNormaliseFamInst ty2
else return (IdCo, ty2)
; coi <- if isOpenSynTyConApp ty1' || isOpenSynTyConApp ty2'
then do { -- One type family app can't be reduced yet
uUnfilledVar outer swapped tv1 details1 ps_ty2 non_var_ty2
= -- ty2 is not a type variable
case details1 of
- MetaTv (SigTv _) _ -> rigid_variable
- MetaTv info ref1 ->
- do { uMetaVar swapped tv1 info ref1 ps_ty2 non_var_ty2
- ; return IdCo
- }
- SkolemTv _ -> rigid_variable
+ MetaTv (SigTv _) _ -> rigid_variable
+ MetaTv info ref1 ->
+ uMetaVar outer swapped tv1 info ref1 ps_ty2 non_var_ty2
+ SkolemTv _ -> rigid_variable
where
rigid_variable
| isOpenSynTyConApp non_var_ty2
= -- 'non_var_ty2's outermost constructor is a type family,
-- which we may may be able to normalise
- do { (coi2, ty2') <- tcNormalizeFamInst non_var_ty2
+ do { (coi2, ty2') <- tcNormaliseFamInst non_var_ty2
; case coi2 of
IdCo -> -- no progress, but maybe after other instantiations
defer_unification outer swapped (TyVarTy tv1) ps_ty2
context x ~ y to establish that it holds.
If available, we defer original types (rather than those where closed type
-synonyms have already been expanded via tcCoreView). This is as usual, to
+synonyms have already been expanded via tcCoreView). This is, as usual, to
improve error messages.
+We need to both 'unBox' and zonk deferred types. We need to unBox as
+functions, such as TcExpr.tcMonoExpr promise to fill boxes in the expected
+type. We need to zonk as the types go into the kind of the coercion variable
+`cotv' and those are not zonked in Inst.zonkInst. (Maybe it would be better
+to zonk in zonInst instead. Would that be sufficient?)
+
\begin{code}
defer_unification :: Bool -- pop innermost context?
-> SwapFlag
defer_unification outer True ty1 ty2
= defer_unification outer False ty2 ty1
defer_unification outer False ty1 ty2
- = do { ty1' <- zonkTcType ty1
- ; ty2' <- zonkTcType ty2
+ = do { ty1' <- unBox ty1 >>= zonkTcType -- unbox *and* zonk..
+ ; ty2' <- unBox ty2 >>= zonkTcType -- ..see preceding note
; traceTc $ text "deferring:" <+> ppr ty1 <+> text "~" <+> ppr ty2
- ; cotv <- newMetaTyVar TauTv (mkCoKind ty1' ty2')
+ ; cotv <- newMetaCoVar ty1' ty2'
-- put ty1 ~ ty2 in LIE
-- Left means "wanted"
; inst <- (if outer then popErrCtxt else id) $
; return $ ACo $ TyVarTy cotv }
----------------
-uMetaVar :: SwapFlag
+uMetaVar :: Bool -- pop innermost context?
+ -> SwapFlag
-> TcTyVar -> BoxInfo -> IORef MetaDetails
-> TcType -> TcType
- -> TcM ()
+ -> TcM CoercionI
-- tv1 is an un-filled-in meta type variable (maybe boxy, maybe tau)
-- ty2 is not a type variable
-uMetaVar swapped tv1 BoxTv ref1 ps_ty2 non_var_ty2
+uMetaVar outer swapped tv1 BoxTv ref1 ps_ty2 non_var_ty2
= -- tv1 is a BoxTv. So we must unbox ty2, to ensure
-- that any boxes in ty2 are filled with monotypes
--
return () -- This really should *not* happen
Flexi -> return ()
#endif
- ; checkUpdateMeta swapped tv1 ref1 final_ty }
+ ; checkUpdateMeta swapped tv1 ref1 final_ty
+ ; return IdCo
+ }
-uMetaVar swapped tv1 info1 ref1 ps_ty2 non_var_ty2
- = do { final_ty <- checkTauTvUpdate tv1 ps_ty2 -- Occurs check + monotype check
- ; checkUpdateMeta swapped tv1 ref1 final_ty }
+uMetaVar outer swapped tv1 info1 ref1 ps_ty2 non_var_ty2
+ = do { -- Occurs check + monotype check
+ ; mb_final_ty <- checkTauTvUpdate tv1 ps_ty2
+ ; case mb_final_ty of
+ Nothing -> -- tv1 occured in type family parameter
+ defer_unification outer swapped (mkTyVarTy tv1) ps_ty2
+ Just final_ty ->
+ do { checkUpdateMeta swapped tv1 ref1 final_ty
+ ; return IdCo
+ }
+ }
----------------
uUnfilledVars :: Outer
-- Try to update sys-y type variables in preference to ones
-- gotten (say) by instantiating a polymorphic function with
-- a user-written type sig
-
-----------------
-checkUpdateMeta :: SwapFlag
- -> TcTyVar -> IORef MetaDetails -> TcType -> TcM ()
--- Update tv1, which is flexi; occurs check is alrady done
--- The 'check' version does a kind check too
--- We do a sub-kind check here: we might unify (a b) with (c d)
--- where b::*->* and d::*; this should fail
-
-checkUpdateMeta swapped tv1 ref1 ty2
- = do { checkKinds swapped tv1 ty2
- ; updateMeta tv1 ref1 ty2 }
-
-updateMeta :: TcTyVar -> IORef MetaDetails -> TcType -> TcM ()
-updateMeta tv1 ref1 ty2
- = ASSERT( isMetaTyVar tv1 )
- ASSERT( isBoxyTyVar tv1 || isTauTy ty2 )
- do { ASSERTM2( do { details <- readMetaTyVar tv1; return (isFlexi details) }, ppr tv1 )
- ; traceTc (text "updateMeta" <+> ppr tv1 <+> text ":=" <+> ppr ty2)
- ; writeMutVar ref1 (Indirect ty2)
- }
-
-----------------
-checkKinds swapped tv1 ty2
--- We're about to unify a type variable tv1 with a non-tyvar-type ty2.
--- ty2 has been zonked at this stage, which ensures that
--- its kind has as much boxity information visible as possible.
- | tk2 `isSubKind` tk1 = returnM ()
-
- | otherwise
- -- Either the kinds aren't compatible
- -- (can happen if we unify (a b) with (c d))
- -- or we are unifying a lifted type variable with an
- -- unlifted type: e.g. (id 3#) is illegal
- = addErrCtxtM (unifyKindCtxt swapped tv1 ty2) $
- unifyKindMisMatch k1 k2
- where
- (k1,k2) | swapped = (tk2,tk1)
- | otherwise = (tk1,tk2)
- tk1 = tyVarKind tv1
- tk2 = typeKind ty2
-
-----------------
-checkTauTvUpdate :: TcTyVar -> TcType -> TcM TcType
--- (checkTauTvUpdate tv ty)
--- We are about to update the TauTv tv with ty.
--- Check (a) that tv doesn't occur in ty (occurs check)
--- (b) that ty is a monotype
--- Furthermore, in the interest of (b), if you find an
--- empty box (BoxTv that is Flexi), fill it in with a TauTv
---
--- Returns the (non-boxy) type to update the type variable with, or fails
-
-checkTauTvUpdate orig_tv orig_ty
- = go orig_ty
- where
- go (TyConApp tc tys)
- | isSynTyCon tc = go_syn tc tys
- | otherwise = do { tys' <- mappM go tys; return (TyConApp tc tys') }
- go (NoteTy _ ty2) = go ty2 -- Discard free-tyvar annotations
- go (PredTy p) = do { p' <- go_pred p; return (PredTy p') }
- go (FunTy arg res) = do { arg' <- go arg; res' <- go res; return (FunTy arg' res') }
- go (AppTy fun arg) = do { fun' <- go fun; arg' <- go arg; return (mkAppTy fun' arg') }
- -- NB the mkAppTy; we might have instantiated a
- -- type variable to a type constructor, so we need
- -- to pull the TyConApp to the top.
- go (ForAllTy tv ty) = notMonoType orig_ty -- (b)
-
- go (TyVarTy tv)
- | orig_tv == tv = occurCheck tv orig_ty -- (a)
- | isTcTyVar tv = go_tyvar tv (tcTyVarDetails tv)
- | otherwise = return (TyVarTy tv)
- -- Ordinary (non Tc) tyvars
- -- occur inside quantified types
-
- go_pred (ClassP c tys) = do { tys' <- mapM go tys; return (ClassP c tys') }
- go_pred (IParam n ty) = do { ty' <- go ty; return (IParam n ty') }
- go_pred (EqPred t1 t2) = do { t1' <- go t1; t2' <- go t2; return (EqPred t1' t2') }
-
- go_tyvar tv (SkolemTv _) = return (TyVarTy tv)
- go_tyvar tv (MetaTv box ref)
- = do { cts <- readMutVar ref
- ; case cts of
- Indirect ty -> go ty
- Flexi -> case box of
- BoxTv -> fillBoxWithTau tv ref
- other -> return (TyVarTy tv)
- }
-
- -- go_syn is called for synonyms only
- -- See Note [Type synonyms and the occur check]
- go_syn tc tys
- | not (isTauTyCon tc)
- = notMonoType orig_ty -- (b) again
- | otherwise
- = do { (msgs, mb_tys') <- tryTc (mapM go tys)
- ; case mb_tys' of
- Just tys' -> return (TyConApp tc tys')
- -- Retain the synonym (the common case)
- Nothing | isOpenTyCon tc
- -> notMonoArgs (TyConApp tc tys)
- -- Synonym families must have monotype args
- | otherwise
- -> go (expectJust "checkTauTvUpdate"
- (tcView (TyConApp tc tys)))
- -- Try again, expanding the synonym
- }
-
-fillBoxWithTau :: BoxyTyVar -> IORef MetaDetails -> TcM TcType
--- (fillBoxWithTau tv ref) fills ref with a freshly allocated
--- tau-type meta-variable, whose print-name is the same as tv
--- Choosing the same name is good: when we instantiate a function
--- we allocate boxy tyvars with the same print-name as the quantified
--- tyvar; and then we often fill the box with a tau-tyvar, and again
--- we want to choose the same name.
-fillBoxWithTau tv ref
- = do { tv' <- tcInstTyVar tv -- Do not gratuitously forget
- ; let tau = mkTyVarTy tv' -- name of the type variable
- ; writeMutVar ref (Indirect tau)
- ; return tau }
\end{code}
-Note [Type synonyms and the occur check]
-~~~~~~~~~~~~~~~~~~~~
-Basically we want to update tv1 := ps_ty2
-because ps_ty2 has type-synonym info, which improves later error messages
-
-But consider
- type A a = ()
-
- f :: (A a -> a -> ()) -> ()
- f = \ _ -> ()
-
- x :: ()
- x = f (\ x p -> p x)
-
-In the application (p x), we try to match "t" with "A t". If we go
-ahead and bind t to A t (= ps_ty2), we'll lead the type checker into
-an infinite loop later.
-But we should not reject the program, because A t = ().
-Rather, we should bind t to () (= non_var_ty2).
-
\begin{code}
refineBox :: TcType -> TcM TcType
-- Unbox the outer box of a boxy type (if any)
msg = vcat [ptext SLIT("When matching") <+> quotes (ppr (mkForAllTys tvs' phi1')),
ptext SLIT(" and") <+> quotes (ppr (mkForAllTys tvs' phi2'))]
-------------------
-unifyKindCtxt swapped tv1 ty2 tidy_env -- not swapped => tv1 expected, ty2 inferred
- -- tv1 and ty2 are zonked already
- = returnM msg
- where
- msg = (env2, ptext SLIT("When matching the kinds of") <+>
- sep [quotes pp_expected <+> ptext SLIT("and"), quotes pp_actual])
-
- (pp_expected, pp_actual) | swapped = (pp2, pp1)
- | otherwise = (pp1, pp2)
- (env1, tv1') = tidyOpenTyVar tidy_env tv1
- (env2, ty2') = tidyOpenType env1 ty2
- pp1 = ppr tv1' <+> dcolon <+> ppr (tyVarKind tv1)
- pp2 = ppr ty2' <+> dcolon <+> ppr (typeKind ty2)
-
+-----------------------
unifyMisMatch outer swapped ty1 ty2
= do { (env, msg) <- if swapped then misMatchMsg ty2 ty1
else misMatchMsg ty1 ty2
; if outer then popErrCtxt (failWithTcM (env, msg))
else failWithTcM (env, msg)
}
-
------------------------
-notMonoType ty
- = do { ty' <- zonkTcType ty
- ; env0 <- tcInitTidyEnv
- ; let (env1, tidy_ty) = tidyOpenType env0 ty'
- msg = ptext SLIT("Cannot match a monotype with") <+> quotes (ppr tidy_ty)
- ; failWithTcM (env1, msg) }
-
-notMonoArgs ty
- = do { ty' <- zonkTcType ty
- ; env0 <- tcInitTidyEnv
- ; let (env1, tidy_ty) = tidyOpenType env0 ty'
- msg = ptext SLIT("Arguments of synonym family must be monotypes") <+> quotes (ppr tidy_ty)
- ; failWithTcM (env1, msg) }
-
-occurCheck tyvar ty
- = do { env0 <- tcInitTidyEnv
- ; ty' <- zonkTcType ty
- ; let (env1, tidy_tyvar) = tidyOpenTyVar env0 tyvar
- (env2, tidy_ty) = tidyOpenType env1 ty'
- extra = sep [ppr tidy_tyvar, char '=', ppr tidy_ty]
- ; failWithTcM (env2, hang msg 2 extra) }
- where
- msg = ptext SLIT("Occurs check: cannot construct the infinite type:")
\end{code}
kindOccurCheckErr tyvar ty
= hang (ptext SLIT("Occurs check: cannot construct the infinite kind:"))
2 (sep [ppr tyvar, char '=', ppr ty])
-
-unifyKindMisMatch ty1 ty2
- = zonkTcKind ty1 `thenM` \ ty1' ->
- zonkTcKind ty2 `thenM` \ ty2' ->
- let
- msg = hang (ptext SLIT("Couldn't match kind"))
- 2 (sep [quotes (ppr ty1'),
- ptext SLIT("against"),
- quotes (ppr ty2')])
- in
- failWithTc msg
\end{code}
\begin{code}
projects / ghc-hetmet.git / blobdiff