%
+% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
-\section{Type subsumption and unification}
+
+Type subsumption and unification
\begin{code}
module TcUnify (
--------------------------------
-- Holes
- tcInfer, subFunTys, unBox, stripBoxyType, withBox,
+ tcInfer, subFunTys, unBox, refineBox, refineBoxToTau, withBox,
boxyUnify, boxyUnifyList, zapToMonotype,
boxySplitListTy, boxySplitTyConApp, boxySplitAppTy,
wrapFunResCoercion
#include "HsVersions.h"
-import HsSyn ( ExprCoFn(..), idCoercion, isIdCoercion, (<.>) )
-import TypeRep ( Type(..), PredType(..) )
-
-import TcMType ( lookupTcTyVar, LookupTyVarResult(..),
- tcInstSkolType, tcInstBoxyTyVar, newKindVar, newMetaTyVar,
- newBoxyTyVar, newBoxyTyVarTys, readFilledBox,
- readMetaTyVar, writeMetaTyVar, newFlexiTyVarTy,
- tcInstSkolTyVars, tcInstTyVar,
- zonkTcKind, zonkType, zonkTcType, zonkTcTyVarsAndFV,
- readKindVar, writeKindVar )
-import TcSimplify ( tcSimplifyCheck )
-import TcEnv ( tcGetGlobalTyVars, findGlobals )
-import TcIface ( checkWiredInTyCon )
+import HsSyn
+import TypeRep
+
+import TcMType
+import TcSimplify
+import TcEnv
+import TcTyFuns
+import TcIface
import TcRnMonad -- TcType, amongst others
-import TcType ( TcKind, TcType, TcTyVar, BoxyTyVar, TcTauType,
- BoxySigmaType, BoxyRhoType, BoxyType,
- TcTyVarSet, TcThetaType, TcTyVarDetails(..), BoxInfo(..),
- SkolemInfo( GenSkol, UnkSkol ), MetaDetails(..), isImmutableTyVar,
- pprSkolTvBinding, isTauTy, isTauTyCon, isSigmaTy,
- mkFunTy, mkFunTys, mkTyConApp, isMetaTyVar,
- tcSplitForAllTys, tcSplitAppTy_maybe, tcSplitFunTys, mkTyVarTys,
- tcSplitSigmaTy, tyVarsOfType, mkPhiTy, mkTyVarTy, mkPredTy,
- typeKind, mkForAllTys, mkAppTy, isBoxyTyVar,
- exactTyVarsOfType,
- tidyOpenType, tidyOpenTyVar, tidyOpenTyVars,
- pprType, tidyKind, tidySkolemTyVar, isSkolemTyVar, tcView,
- TvSubst, mkTvSubst, zipTyEnv, zipOpenTvSubst, emptyTvSubst,
- substTy, substTheta,
- lookupTyVar, extendTvSubst )
-import Kind ( Kind(..), SimpleKind, KindVar, isArgTypeKind,
- openTypeKind, liftedTypeKind, unliftedTypeKind,
- mkArrowKind, defaultKind,
- isOpenTypeKind, argTypeKind, isLiftedTypeKind, isUnliftedTypeKind,
- isSubKind, pprKind, splitKindFunTys )
-import TysPrim ( alphaTy, betaTy )
-import Inst ( newDicts, instToId )
-import TyCon ( TyCon, tyConArity, tyConTyVars, isSynTyCon )
-import TysWiredIn ( listTyCon )
-import Id ( Id, mkSysLocal )
-import Var ( Var, varName, tyVarKind, isTcTyVar, tcTyVarDetails )
-import VarSet ( emptyVarSet, mkVarSet, unitVarSet, unionVarSet, elemVarSet, varSetElems,
- extendVarSet, intersectsVarSet, extendVarSetList )
+import TcType
+import Type
+import Coercion
+import TysPrim
+import Inst
+import TyCon
+import TysWiredIn
+import Var
+import VarSet
import VarEnv
-import Name ( Name, isSystemName )
-import ErrUtils ( Message )
-import Maybes ( expectJust, isNothing )
-import BasicTypes ( Arity )
-import UniqSupply ( uniqsFromSupply )
-import Util ( notNull, equalLength )
+import Name
+import ErrUtils
+import Maybes
+import BasicTypes
+import Util
import Outputable
-
--- Assertion imports
-#ifdef DEBUG
-import TcType ( isBoxyTy, isFlexi )
-#endif
+import Unique
\end{code}
%************************************************************************
tcInfer tc_infer
= do { box <- newBoxyTyVar openTypeKind
; res <- tc_infer (mkTyVarTy box)
- ; res_ty <- readFilledBox box -- Guaranteed filled-in by now
+ ; res_ty <- {- pprTrace "tcInfer" (ppr (mkTyVarTy box)) $ -} readFilledBox box -- Guaranteed filled-in by now
; return (res, res_ty) }
-\end{code}
+\end{code}
%************************************************************************
-> Arity -- Expected # of args
-> BoxyRhoType -- res_ty
-> ([BoxySigmaType] -> BoxyRhoType -> TcM a)
- -> TcM (ExprCoFn, a)
+ -> TcM (HsWrapper, a)
-- Attempt to decompse res_ty to have enough top-level arrows to
-- match the number of patterns in the match group
--
-- If (subFunTys n_args res_ty thing_inside) = (co_fn, res)
-- and the inner call to thing_inside passes args: [a1,...,an], b
--- then co_fn :: (a1 -> ... -> an -> b) -> res_ty
+-- then co_fn :: (a1 -> ... -> an -> b) ~ res_ty
--
-- Note that it takes a BoxyRho type, and guarantees to return a BoxyRhoType
where
-- In 'loop', the parameter 'arg_tys' accumulates
-- the arg types so far, in *reverse order*
+ -- INVARIANT: res_ty :: *
loop n args_so_far res_ty
| Just res_ty' <- tcView res_ty = loop n args_so_far res_ty'
loop n args_so_far res_ty
| isSigmaTy res_ty -- Do this before checking n==0, because we
-- guarantee to return a BoxyRhoType, not a BoxySigmaType
- = do { (gen_fn, (co_fn, res)) <- tcGen res_ty emptyVarSet $ \ res_ty' ->
+ = do { (gen_fn, (co_fn, res)) <- tcGen res_ty emptyVarSet $ \ _ res_ty' ->
loop n args_so_far res_ty'
; return (gen_fn <.> co_fn, res) }
loop 0 args_so_far res_ty
= do { res <- thing_inside (reverse args_so_far) res_ty
- ; return (idCoercion, res) }
+ ; return (idHsWrapper, res) }
loop n args_so_far (FunTy arg_ty res_ty)
= do { (co_fn, res) <- loop (n-1) (arg_ty:args_so_far) res_ty
-- error message on failure
loop n args_so_far res_ty@(AppTy _ _)
= do { [arg_ty',res_ty'] <- newBoxyTyVarTys [argTypeKind, openTypeKind]
- ; (_, mb_unit) <- tryTcErrs $ boxyUnify res_ty (FunTy arg_ty' res_ty')
- ; if isNothing mb_unit then bale_out args_so_far
- else loop n args_so_far (FunTy arg_ty' res_ty') }
+ ; (_, mb_coi) <- tryTcErrs $ boxyUnify res_ty (FunTy arg_ty' res_ty')
+ ; if isNothing mb_coi then bale_out args_so_far
+ else do { case expectJust "subFunTys" mb_coi of
+ IdCo -> return ()
+ ACo co -> traceTc (text "you're dropping a coercion: " <+> ppr co)
+ ; loop n args_so_far (FunTy arg_ty' res_ty')
+ }
+ }
loop n args_so_far (TyVarTy tv)
- | not (isImmutableTyVar tv)
+ | isTyConableTyVar tv
= do { cts <- readMetaTyVar tv
; case cts of
Indirect ty -> loop n args_so_far ty
Flexi -> do { (res_ty:arg_tys) <- withMetaTvs tv kinds mk_res_ty
; res <- thing_inside (reverse args_so_far ++ arg_tys) res_ty
- ; return (idCoercion, res) } }
+ ; return (idHsWrapper, res) } }
where
mk_res_ty (res_ty' : arg_tys') = mkFunTys arg_tys' res_ty'
+ mk_res_ty [] = panic "TcUnify.mk_res_ty1"
kinds = openTypeKind : take n (repeat argTypeKind)
-- Note argTypeKind: the args can have an unboxed type,
-- but not an unboxed tuple.
return (args ++ args_so_far)
loop n_req args_so_far (AppTy fun arg)
+ | n_req > 0
= loop (n_req - 1) (arg:args_so_far) fun
loop n_req args_so_far (TyVarTy tv)
- | not (isImmutableTyVar tv)
+ | isTyConableTyVar tv
+ , res_kind `isSubKind` tyVarKind tv
= do { cts <- readMetaTyVar tv
; case cts of
Indirect ty -> loop n_req args_so_far ty
- Flexi -> do { arg_tys <- withMetaTvs tv arg_kinds mk_res_ty
+ Flexi -> do { arg_tys <- withMetaTvs tv arg_kinds mk_res_ty
; return (arg_tys ++ args_so_far) }
}
where
mk_res_ty arg_tys' = mkTyConApp tc arg_tys'
- arg_kinds = map tyVarKind (take n_req (tyConTyVars tc))
+ (arg_kinds, res_kind) = splitKindFunTysN n_req (tyConKind tc)
loop _ _ _ = boxySplitFailure (mkTyConApp tc (mkTyVarTys (tyConTyVars tc))) orig_ty
----------------------
boxySplitAppTy :: BoxyRhoType -- Type to split: m a
-> TcM (BoxySigmaType, BoxySigmaType) -- Returns m, a
--- Assumes (m: * -> k), where k is the kind of the incoming type
+-- 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
boxySplitAppTy orig_ty
= return (fun_ty, arg_ty)
loop (TyVarTy tv)
- | not (isImmutableTyVar 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
+ Flexi -> do { [fun_ty,arg_ty] <- withMetaTvs tv kinds mk_res_ty
; return (fun_ty, arg_ty) } }
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
withBox kind thing_inside
= do { box_tv <- newMetaTyVar BoxTv kind
; res <- thing_inside (mkTyVarTy box_tv)
- ; ty <- readFilledBox box_tv
+ ; ty <- {- pprTrace "with_box" (ppr (mkTyVarTy box_tv)) $ -} readFilledBox box_tv
; return (res, ty) }
\end{code}
\begin{code}
preSubType :: [TcTyVar] -- Quantified type variables
-> TcTyVarSet -- Subset of quantified type variables
- -- that can be instantiated with boxy types
+ -- see Note [Pre-sub boxy]
-> TcType -- The rho-type part; quantified tyvars scopes over this
-> BoxySigmaType -- Matching type from the context
-> TcM [TcType] -- Types to instantiate the tyvars
-- info from the pre-subsumption, if there is any
-- a boxy type variable otherwise
--
--- The 'btvs' are a subset of 'qtvs'. They are the ones we can
--- instantiate to a boxy type variable, because they'll definitely be
--- filled in later. This isn't always the case; sometimes we have type
--- variables mentioned in the context of the type, but not the body;
--- f :: forall a b. C a b => a -> a
--- Then we may land up with an unconstrained 'b', so we want to
--- instantiate it to a monotype (non-boxy) type variable
+-- Note [Pre-sub boxy]
+-- The 'btvs' are a subset of 'qtvs'. They are the ones we can
+-- instantiate to a boxy type variable, because they'll definitely be
+-- filled in later. This isn't always the case; sometimes we have type
+-- variables mentioned in the context of the type, but not the body;
+-- f :: forall a b. C a b => a -> a
+-- Then we may land up with an unconstrained 'b', so we want to
+-- instantiate it to a monotype (non-boxy) type variable
+--
+-- The 'qtvs' that are *neither* fixed by the pre-subsumption, *nor* are in 'btvs',
+-- are instantiated to TauTv meta variables.
preSubType qtvs btvs qty expected_ty
= do { tys <- mapM inst_tv qtvs
-- "Boxy types: inference for higher rank types and impredicativity"
boxySubMatchType tmpl_tvs tmpl_ty boxy_ty
- = go tmpl_ty emptyVarSet boxy_ty
+ = go tmpl_tvs tmpl_ty emptyVarSet boxy_ty
where
- go t_ty b_tvs b_ty
- | Just t_ty' <- tcView t_ty = go t_ty' b_tvs b_ty
- | Just b_ty' <- tcView b_ty = go t_ty b_tvs b_ty'
+ go t_tvs t_ty b_tvs b_ty
+ | Just t_ty' <- tcView t_ty = go t_tvs t_ty' b_tvs b_ty
+ | Just b_ty' <- tcView b_ty = go t_tvs t_ty b_tvs b_ty'
- go (TyVarTy _) b_tvs b_ty = emptyTvSubst -- Rule S-ANY; no bindings
+ go t_tvs (TyVarTy _) b_tvs b_ty = emptyTvSubst -- Rule S-ANY; no bindings
-- Rule S-ANY covers (a) type variables and (b) boxy types
-- in the template. Both look like a TyVarTy.
-- See Note [Sub-match] below
- go t_ty b_tvs b_ty
+ go t_tvs t_ty b_tvs b_ty
| isSigmaTy t_ty, (tvs, _, t_tau) <- tcSplitSigmaTy t_ty
- = go t_tau b_tvs b_ty -- Rule S-SPEC
+ = go (t_tvs `delVarSetList` tvs) t_tau b_tvs b_ty -- Rule S-SPEC
+ -- Under a forall on the left, if there is shadowing,
+ -- do not bind! Hence the delVarSetList.
| isSigmaTy b_ty, (tvs, _, b_tau) <- tcSplitSigmaTy b_ty
- = go t_ty (extendVarSetList b_tvs tvs) b_ty -- Rule S-SKOL
+ = go t_tvs t_ty (extendVarSetList b_tvs tvs) b_tau -- Rule S-SKOL
+ -- Add to the variables we must not bind to
-- NB: it's *important* to discard the theta part. Otherwise
-- consider (forall a. Eq a => a -> b) ~<~ (Int -> Int -> Bool)
-- and end up with a completely bogus binding (b |-> Bool), by lining
-- This pre-subsumption stuff can return too few bindings, but it
-- must *never* return bogus info.
- go (FunTy arg1 res1) b_tvs (FunTy arg2 res2) -- Rule S-FUN
- = boxy_match tmpl_tvs arg1 b_tvs arg2 (go res1 b_tvs res2)
+ go t_tvs (FunTy arg1 res1) b_tvs (FunTy arg2 res2) -- Rule S-FUN
+ = boxy_match t_tvs arg1 b_tvs arg2 (go t_tvs res1 b_tvs res2)
-- Match the args, and sub-match the results
- go t_ty b_tvs b_ty = boxy_match tmpl_tvs t_ty b_tvs b_ty emptyTvSubst
+ go t_tvs t_ty b_tvs b_ty = boxy_match t_tvs t_ty b_tvs b_ty emptyTvSubst
-- Otherwise defer to boxy matching
-- This covers TyConApp, AppTy, PredTy
\end{code}
-- It does no unification, and cannot fail
--
-- Precondition: the arg lengths are equal
--- Precondition: none of the template type variables appear in the [BoxySigmaType]
--- Precondition: any nested quantifiers in either type differ from
--- the template type variables passed as arguments
+-- Precondition: none of the template type variables appear anywhere in the [BoxySigmaType]
--
------------
boxy_match_s tmpl_tvs [] boxy_tvs [] subst
= subst
boxy_match_s tmpl_tvs (t_ty:t_tys) boxy_tvs (b_ty:b_tys) subst
- = boxy_match_s tmpl_tvs t_tys boxy_tvs b_tys $
- boxy_match tmpl_tvs t_ty boxy_tvs b_ty subst
+ = boxy_match tmpl_tvs t_ty boxy_tvs b_ty $
+ boxy_match_s tmpl_tvs t_tys boxy_tvs b_tys subst
+boxy_match_s tmpl_tvs _ boxy_tvs _ subst
+ = panic "boxy_match_s" -- Lengths do not match
+
------------
boxy_match :: TcTyVarSet -> TcType -- Template
| Just t_ty' <- tcView t_ty = go t_ty' b_ty
| Just b_ty' <- tcView b_ty = go t_ty b_ty'
- go (ForAllTy _ ty1) (ForAllTy tv2 ty2)
- = boxy_match tmpl_tvs ty1 (boxy_tvs `extendVarSet` tv2) ty2 subst
+ go ty1 ty2 -- C.f. the isSigmaTy case for boxySubMatchType
+ | isSigmaTy ty1
+ , (tvs1, _, tau1) <- tcSplitSigmaTy ty1
+ , (tvs2, _, tau2) <- tcSplitSigmaTy ty2
+ , equalLength tvs1 tvs2
+ = boxy_match (tmpl_tvs `delVarSetList` tvs1) tau1
+ (boxy_tvs `extendVarSetList` tvs2) tau2 subst
go (TyConApp tc1 tys1) (TyConApp tc2 tys2)
- | tc1 == tc2 = go_s tys1 tys2
+ | tc1 == tc2
+ , not $ isOpenSynTyCon tc1
+ = go_s tys1 tys2
go (FunTy arg1 res1) (FunTy arg2 res2)
= go_s [arg1,res1] [arg2,res2]
go (TyVarTy tv) b_ty
| tv `elemVarSet` tmpl_tvs -- Template type variable in the template
- , not (intersectsVarSet boxy_tvs (tyVarsOfType orig_boxy_ty))
+ , boxy_tvs `disjointVarSet` tyVarsOfType orig_boxy_ty
, typeKind b_ty `isSubKind` tyVarKind tv -- See Note [Matching kinds]
= extendTvSubst subst tv boxy_ty'
| otherwise
a place expecting a value of type expected_ty.
It returns a coercion function
- co_fn :: offered_ty -> expected_ty
+ co_fn :: offered_ty ~ expected_ty
which takes an HsExpr of type offered_ty into one of type
expected_ty.
\begin{code}
-----------------
-tcSubExp :: BoxySigmaType -> BoxySigmaType -> TcM ExprCoFn -- Locally used only
+tcSubExp :: BoxySigmaType -> BoxySigmaType -> TcM HsWrapper -- Locally used only
-- (tcSub act exp) checks that
-- act <= exp
tcSubExp actual_ty expected_ty
- = addErrCtxtM (unifyCtxt actual_ty expected_ty)
- (tc_sub True actual_ty actual_ty expected_ty expected_ty)
-
-tcFunResTy :: Name -> BoxySigmaType -> BoxySigmaType -> TcM ExprCoFn -- Locally used only
+ = -- addErrCtxtM (unifyCtxt actual_ty expected_ty) $
+ -- Adding the error context here leads to some very confusing error
+ -- messages, such as "can't match forall a. a->a with forall a. a->a"
+ -- Example is tcfail165:
+ -- do var <- newEmptyMVar :: IO (MVar (forall a. Show a => a -> String))
+ -- putMVar var (show :: forall a. Show a => a -> String)
+ -- Here the info does not flow from the 'var' arg of putMVar to its 'show' arg
+ -- but after zonking it looks as if it does!
+ --
+ -- So instead I'm adding the error context when moving from tc_sub to u_tys
+
+ traceTc (text "tcSubExp" <+> ppr actual_ty <+> ppr expected_ty) >>
+ tc_sub SubOther actual_ty actual_ty False expected_ty expected_ty
+
+tcFunResTy :: Name -> BoxySigmaType -> BoxySigmaType -> TcM HsWrapper -- Locally used only
tcFunResTy fun actual_ty expected_ty
- = addErrCtxtM (checkFunResCtxt fun actual_ty expected_ty) $
- (tc_sub True actual_ty actual_ty expected_ty expected_ty)
+ = traceTc (text "tcFunResTy" <+> ppr actual_ty <+> ppr expected_ty) >>
+ tc_sub (SubFun fun) actual_ty actual_ty False expected_ty expected_ty
-----------------
-tc_sub :: Outer -- See comments with uTys
+data SubCtxt = SubDone -- Error-context already pushed
+ | SubFun Name -- Context is tcFunResTy
+ | SubOther -- Context is something else
+
+tc_sub :: SubCtxt -- How to add an error-context
-> BoxySigmaType -- actual_ty, before expanding synonyms
-> BoxySigmaType -- ..and after
+ -> InBox -- True <=> expected_ty is inside a box
-> BoxySigmaType -- expected_ty, before
-> BoxySigmaType -- ..and after
- -> TcM ExprCoFn
+ -> TcM HsWrapper
+ -- The acual_ty is never inside a box
+-- IMPORTANT pre-condition: if the args contain foralls, the bound type
+-- variables are visible non-monadically
+-- (i.e. tha args are sufficiently zonked)
+-- This invariant is needed so that we can "see" the foralls, ad
+-- e.g. in the SPEC rule where we just use splitSigmaTy
+
+tc_sub sub_ctxt act_sty act_ty exp_ib exp_sty exp_ty
+ = traceTc (text "tc_sub" <+> ppr act_ty $$ ppr exp_ty) >>
+ tc_sub1 sub_ctxt act_sty act_ty exp_ib exp_sty exp_ty
+ -- This indirection is just here to make
+ -- it easy to insert a debug trace!
-tc_sub outer act_sty act_ty exp_sty exp_ty
- | Just exp_ty' <- tcView exp_ty = tc_sub False act_sty act_ty exp_sty exp_ty'
-tc_sub outer act_sty act_ty exp_sty exp_ty
- | Just act_ty' <- tcView act_ty = tc_sub False act_sty act_ty' exp_sty exp_ty
+tc_sub1 sub_ctxt act_sty act_ty exp_ib exp_sty exp_ty
+ | Just exp_ty' <- tcView exp_ty = tc_sub sub_ctxt act_sty act_ty exp_ib exp_sty exp_ty'
+tc_sub1 sub_ctxt act_sty act_ty exp_ib exp_sty exp_ty
+ | Just act_ty' <- tcView act_ty = tc_sub sub_ctxt act_sty act_ty' exp_ib exp_sty exp_ty
-----------------------------------
-- Rule SBOXY, plus other cases when act_ty is a type variable
-- Just defer to boxy matching
-- This rule takes precedence over SKOL!
-tc_sub outer act_sty (TyVarTy tv) exp_sty exp_ty
- = do { uVar outer False tv False exp_sty exp_ty
- ; return idCoercion }
+tc_sub1 sub_ctxt act_sty (TyVarTy tv) exp_ib exp_sty exp_ty
+ = do { traceTc (text "tc_sub1 - case 1")
+ ; coi <- addSubCtxt sub_ctxt act_sty exp_sty $
+ uVar True False tv exp_ib exp_sty exp_ty
+ ; traceTc (case coi of
+ IdCo -> text "tc_sub1 (Rule SBOXY) IdCo"
+ ACo co -> text "tc_sub1 (Rule SBOXY) ACo" <+> ppr co)
+ ; return $ case coi of
+ IdCo -> idHsWrapper
+ ACo co -> WpCo co
+ }
-----------------------------------
-- Skolemisation case (rule SKOL)
-- g :: Ord b => b->b
-- Consider f g !
-tc_sub outer act_sty act_ty exp_sty exp_ty
- | isSigmaTy exp_ty
- = do { (gen_fn, co_fn) <- tcGen exp_ty act_tvs $ \ body_exp_ty ->
- tc_sub False act_sty act_ty body_exp_ty body_exp_ty
+tc_sub1 sub_ctxt act_sty act_ty exp_ib exp_sty exp_ty
+ | isSigmaTy exp_ty
+ = do { traceTc (text "tc_sub1 - case 2") ;
+ if exp_ib then -- SKOL does not apply if exp_ty is inside a box
+ defer_to_boxy_matching sub_ctxt act_sty act_ty exp_ib exp_sty exp_ty
+ else do
+ { (gen_fn, co_fn) <- tcGen exp_ty act_tvs $ \ _ body_exp_ty ->
+ tc_sub sub_ctxt act_sty act_ty False body_exp_ty body_exp_ty
; return (gen_fn <.> co_fn) }
+ }
where
act_tvs = tyVarsOfType act_ty
-- It's really important to check for escape wrt
-- expected_ty: Int -> Int
-- co_fn e = e Int dOrdInt
-tc_sub outer act_sty actual_ty exp_sty expected_ty
+tc_sub1 sub_ctxt act_sty actual_ty exp_ib exp_sty expected_ty
-- Implements the new SPEC rule in the Appendix of the paper
-- "Boxy types: inference for higher rank types and impredicativity"
-- (This appendix isn't in the published version.)
-- Pre-subsumpion finds a|->Int, and that works fine, whereas
-- just running full subsumption would fail.
| isSigmaTy actual_ty
- = do { -- Perform pre-subsumption, and instantiate
+ = do { traceTc (text "tc_sub1 - case 3")
+ ; -- Perform pre-subsumption, and instantiate
-- the type with info from the pre-subsumption;
-- boxy tyvars if pre-subsumption gives no info
let (tyvars, theta, tau) = tcSplitSigmaTy actual_ty
tau_tvs = exactTyVarsOfType tau
- ; inst_tys <- preSubType tyvars tau_tvs tau expected_ty
+ ; inst_tys <- if exp_ib then -- Inside a box, do not do clever stuff
+ do { tyvars' <- mapM tcInstBoxyTyVar tyvars
+ ; return (mkTyVarTys tyvars') }
+ else -- Outside, do clever stuff
+ preSubType tyvars tau_tvs tau expected_ty
; let subst' = zipOpenTvSubst tyvars inst_tys
tau' = substTy subst' tau
-- Perform a full subsumption check
- ; co_fn <- tc_sub False tau' tau' exp_sty expected_ty
+ ; traceTc (text "tc_sub_spec" <+> vcat [ppr actual_ty,
+ ppr tyvars <+> ppr theta <+> ppr tau,
+ ppr tau'])
+ ; co_fn2 <- tc_sub sub_ctxt tau' tau' exp_ib exp_sty expected_ty
-- Deal with the dictionaries
- ; dicts <- newDicts InstSigOrigin (substTheta subst' theta)
- ; extendLIEs dicts
- ; let inst_fn = CoApps (CoTyApps CoHole inst_tys)
- (map instToId dicts)
- ; return (co_fn <.> inst_fn) }
+ -- The origin gives a helpful origin when we have
+ -- a function with type f :: Int -> forall a. Num a => ...
+ -- This way the (Num a) dictionary gets an OccurrenceOf f origin
+ ; let orig = case sub_ctxt of
+ SubFun n -> OccurrenceOf n
+ other -> InstSigOrigin -- Unhelpful
+ ; co_fn1 <- instCall orig inst_tys (substTheta subst' theta)
+ ; return (co_fn2 <.> co_fn1) }
-----------------------------------
-- Function case (rule F1)
-tc_sub _ _ (FunTy act_arg act_res) _ (FunTy exp_arg exp_res)
- = tc_sub_funs act_arg act_res exp_arg exp_res
+tc_sub1 sub_ctxt act_sty (FunTy act_arg act_res) exp_ib exp_sty (FunTy exp_arg exp_res)
+ = do { traceTc (text "tc_sub1 - case 4")
+ ; addSubCtxt sub_ctxt act_sty exp_sty $
+ tc_sub_funs act_arg act_res exp_ib exp_arg exp_res
+ }
-- Function case (rule F2)
-tc_sub outer act_sty act_ty@(FunTy act_arg act_res) exp_sty (TyVarTy exp_tv)
+tc_sub1 sub_ctxt act_sty act_ty@(FunTy act_arg act_res) _ exp_sty (TyVarTy exp_tv)
| isBoxyTyVar exp_tv
- = do { cts <- readMetaTyVar exp_tv
+ = addSubCtxt sub_ctxt act_sty exp_sty $
+ do { traceTc (text "tc_sub1 - case 5")
+ ; cts <- readMetaTyVar exp_tv
; case cts of
- Indirect ty -> do { u_tys outer False act_sty act_ty True exp_sty ty
- ; return idCoercion }
- Flexi -> do { [arg_ty,res_ty] <- withMetaTvs exp_tv fun_kinds mk_res_ty
- ; tc_sub_funs act_arg act_res arg_ty res_ty } }
+ Indirect ty -> tc_sub SubDone act_sty act_ty True exp_sty ty
+ Flexi -> do { [arg_ty,res_ty] <- withMetaTvs exp_tv fun_kinds mk_res_ty
+ ; tc_sub_funs act_arg act_res True arg_ty res_ty } }
where
mk_res_ty [arg_ty', res_ty'] = mkFunTy arg_ty' res_ty'
+ mk_res_ty other = panic "TcUnify.mk_res_ty3"
fun_kinds = [argTypeKind, openTypeKind]
-- Everything else: defer to boxy matching
-tc_sub outer act_sty actual_ty exp_sty expected_ty
- = do { u_tys outer False act_sty actual_ty False exp_sty expected_ty
- ; return idCoercion }
+tc_sub1 sub_ctxt act_sty actual_ty exp_ib exp_sty expected_ty@(TyVarTy exp_tv)
+ = do { traceTc (text "tc_sub1 - case 6a" <+> ppr [isBoxyTyVar exp_tv, isMetaTyVar exp_tv, isSkolemTyVar exp_tv, isExistentialTyVar exp_tv,isSigTyVar exp_tv] )
+ ; defer_to_boxy_matching sub_ctxt act_sty actual_ty exp_ib exp_sty expected_ty
+ }
+tc_sub1 sub_ctxt act_sty actual_ty exp_ib exp_sty expected_ty
+ = do { traceTc (text "tc_sub1 - case 6")
+ ; defer_to_boxy_matching sub_ctxt act_sty actual_ty exp_ib exp_sty expected_ty
+ }
-----------------------------------
-tc_sub_funs act_arg act_res exp_arg exp_res
- = do { uTys False act_arg False exp_arg
- ; co_fn_res <- tc_sub False act_res act_res exp_res exp_res
- ; wrapFunResCoercion [exp_arg] co_fn_res }
+defer_to_boxy_matching sub_ctxt act_sty actual_ty exp_ib exp_sty expected_ty
+ = do { coi <- addSubCtxt sub_ctxt act_sty exp_sty $
+ u_tys outer False act_sty actual_ty exp_ib exp_sty expected_ty
+ ; return $ case coi of
+ IdCo -> idHsWrapper
+ ACo co -> WpCo co
+ }
+ where
+ outer = case sub_ctxt of -- Ugh
+ SubDone -> False
+ other -> True
+
+-----------------------------------
+tc_sub_funs act_arg act_res exp_ib exp_arg exp_res
+ = do { arg_coi <- uTys False act_arg exp_ib exp_arg
+ ; co_fn_res <- tc_sub SubDone act_res act_res exp_ib exp_res exp_res
+ ; wrapper1 <- wrapFunResCoercion [exp_arg] co_fn_res
+ ; let wrapper2 = case arg_coi of
+ IdCo -> idHsWrapper
+ ACo co -> WpCo $ FunTy co act_res
+ ; return (wrapper1 <.> wrapper2)
+ }
-----------------------------------
wrapFunResCoercion
:: [TcType] -- Type of args
- -> ExprCoFn -- HsExpr a -> HsExpr b
- -> TcM ExprCoFn -- HsExpr (arg_tys -> a) -> HsExpr (arg_tys -> b)
+ -> HsWrapper -- HsExpr a -> HsExpr b
+ -> TcM HsWrapper -- HsExpr (arg_tys -> a) -> HsExpr (arg_tys -> b)
wrapFunResCoercion arg_tys co_fn_res
- | isIdCoercion co_fn_res = return idCoercion
- | null arg_tys = return co_fn_res
+ | isIdHsWrapper co_fn_res
+ = return idHsWrapper
+ | null arg_tys
+ = return co_fn_res
| otherwise
- = do { us <- newUniqueSupply
- ; let arg_ids = zipWith (mkSysLocal FSLIT("sub")) (uniqsFromSupply us) arg_tys
- ; return (CoLams arg_ids (co_fn_res <.> (CoApps CoHole arg_ids))) }
+ = do { arg_ids <- newSysLocalIds FSLIT("sub") arg_tys
+ ; return (mkWpLams arg_ids <.> co_fn_res <.> mkWpApps arg_ids) }
\end{code}
-> TcTyVarSet -- Extra tyvars that the universally
-- quantified tyvars of expected_ty
-- must not be unified
- -> (BoxyRhoType -> TcM result) -- spec_ty
- -> TcM (ExprCoFn, result)
+ -> ([TcTyVar] -> BoxyRhoType -> TcM result)
+ -> TcM (HsWrapper, result)
-- The expression has type: spec_ty -> expected_ty
tcGen expected_ty extra_tvs thing_inside -- We expect expected_ty to be a forall-type
-- If not, the call is a no-op
- = do { -- We want the GenSkol info in the skolemised type variables to
+ = do { traceTc (text "tcGen")
+ -- We want the GenSkol info in the skolemised type variables to
-- mention the *instantiated* tyvar names, so that we get a
-- good error message "Rigid variable 'a' is bound by (forall a. a->a)"
-- Hence the tiresome but innocuous fixM
- ((forall_tvs, theta, rho_ty), skol_info) <- fixM (\ ~(_, skol_info) ->
+ ; ((tvs', theta', rho'), skol_info) <- fixM (\ ~(_, skol_info) ->
do { (forall_tvs, theta, rho_ty) <- tcInstSkolType skol_info expected_ty
- ; span <- getSrcSpanM
- ; let skol_info = GenSkol forall_tvs (mkPhiTy theta rho_ty) span
+ -- Get loation from monad, not from expected_ty
+ ; let skol_info = GenSkol forall_tvs (mkPhiTy theta rho_ty)
; return ((forall_tvs, theta, rho_ty), skol_info) })
#ifdef DEBUG
; traceTc (text "tcGen" <+> vcat [text "extra_tvs" <+> ppr extra_tvs,
text "expected_ty" <+> ppr expected_ty,
- text "inst ty" <+> ppr forall_tvs <+> ppr theta <+> ppr rho_ty,
- text "free_tvs" <+> ppr free_tvs,
- text "forall_tvs" <+> ppr forall_tvs])
+ text "inst ty" <+> ppr tvs' <+> ppr theta' <+> ppr rho',
+ text "free_tvs" <+> ppr free_tvs])
#endif
-- Type-check the arg and unify with poly type
- ; (result, lie) <- getLIE (thing_inside rho_ty)
+ ; (result, lie) <- getLIE (thing_inside tvs' rho')
-- Check that the "forall_tvs" havn't been constrained
-- The interesting bit here is that we must include the free variables
-- Conclusion: include the free vars of the expected_ty in the
-- list of "free vars" for the signature check.
- ; dicts <- newDicts (SigOrigin skol_info) theta
- ; inst_binds <- tcSimplifyCheck sig_msg forall_tvs dicts lie
+ ; loc <- getInstLoc (SigOrigin skol_info)
+ ; dicts <- newDictBndrs loc theta'
+ ; inst_binds <- tcSimplifyCheck loc tvs' dicts lie
- ; checkSigTyVarsWrt free_tvs forall_tvs
+ ; checkSigTyVarsWrt free_tvs tvs'
; traceTc (text "tcGen:done")
; let
- -- This HsLet binds any Insts which came out of the simplification.
- -- It's a bit out of place here, but using AbsBind involves inventing
- -- a couple of new names which seems worse.
- dict_ids = map instToId dicts
- co_fn = CoTyLams forall_tvs $ CoLams dict_ids $ CoLet inst_binds CoHole
+ -- 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
; returnM (co_fn, result) }
where
free_tvs = tyVarsOfType expected_ty `unionVarSet` extra_tvs
- sig_msg = ptext SLIT("expected type of an expression")
-\end{code}
+\end{code}
non-exported generic functions.
\begin{code}
-boxyUnify :: BoxyType -> BoxyType -> TcM ()
+boxyUnify :: BoxyType -> BoxyType -> TcM CoercionI
-- Acutal and expected, respectively
boxyUnify ty1 ty2
= addErrCtxtM (unifyCtxt ty1 ty2) $
uTysOuter False ty1 False ty2
---------------
-boxyUnifyList :: [BoxyType] -> [BoxyType] -> TcM ()
+boxyUnifyList :: [BoxyType] -> [BoxyType] -> TcM [CoercionI]
-- Arguments should have equal length
-- Acutal and expected types
boxyUnifyList tys1 tys2 = uList boxyUnify tys1 tys2
---------------
-unifyType :: TcTauType -> TcTauType -> TcM ()
+unifyType :: TcTauType -> TcTauType -> TcM CoercionI
-- No boxes expected inside these types
-- Acutal and expected types
unifyType ty1 ty2 -- ty1 expected, ty2 inferred
uTysOuter True ty1 True ty2
---------------
-unifyPred :: PredType -> PredType -> TcM ()
+unifyPred :: PredType -> PredType -> TcM CoercionI
-- Acutal and expected types
unifyPred p1 p2 = addErrCtxtM (unifyCtxt (mkPredTy p1) (mkPredTy p2)) $
- uPred True True p1 True p2
+ uPred True True p1 True p2
-unifyTheta :: TcThetaType -> TcThetaType -> TcM ()
+unifyTheta :: TcThetaType -> TcThetaType -> TcM [CoercionI]
-- Acutal and expected types
unifyTheta theta1 theta2
= do { checkTc (equalLength theta1 theta2)
- (ptext SLIT("Contexts differ in length"))
- ; uList unifyPred theta1 theta2 }
+ (vcat [ptext SLIT("Contexts differ in length"),
+ nest 2 $ parens $ ptext SLIT("Use -fglasgow-exts to allow this")])
+ ; uList unifyPred theta1 theta2
+ }
---------------
-uList :: (a -> a -> TcM ())
- -> [a] -> [a] -> TcM ()
+uList :: (a -> a -> TcM b)
+ -> [a] -> [a] -> TcM [b]
-- Unify corresponding elements of two lists of types, which
--- should be f equal length. We charge down the list explicitly so that
+-- should be of equal length. We charge down the list explicitly so that
-- we can complain if their lengths differ.
-uList unify [] [] = return ()
-uList unify (ty1:tys1) (ty2:tys2) = do { unify ty1 ty2; uList unify tys1 tys2 }
+uList unify [] [] = return []
+uList unify (ty1:tys1) (ty2:tys2) = do { x <- unify ty1 ty2;
+ ; xs <- uList unify tys1 tys2
+ ; return (x:xs)
+ }
uList unify ty1s ty2s = panic "Unify.uList: mismatched type lists!"
\end{code}
%* *
%************************************************************************
-@uTys@ is the heart of the unifier. Each arg happens twice, because
-we want to report errors in terms of synomyms if poss. The first of
+@uTys@ is the heart of the unifier. Each arg occurs twice, because
+we want to report errors in terms of synomyms if possible. The first of
the pair is used in error messages only; it is always the same as the
second, except that if the first is a synonym then the second may be a
de-synonym'd version. This way we get better error messages.
We call the first one \tr{ps_ty1}, \tr{ps_ty2} for ``possible synomym''.
\begin{code}
-type NoBoxes = Bool -- True <=> definitely no boxes in this type
- -- False <=> there might be boxes (always safe)
+type SwapFlag = Bool
+ -- False <=> the two args are (actual, expected) respectively
+ -- True <=> the two args are (expected, actual) respectively
+
+type InBox = Bool -- True <=> we are inside a box
+ -- False <=> we are outside a box
+ -- The importance of this is that if we get "filled-box meets
+ -- filled-box", we'll look into the boxes and unify... but
+ -- we must not allow polytypes. But if we are in a box on
+ -- just one side, then we can allow polytypes
type Outer = Bool -- True <=> this is the outer level of a unification
-- so that the types being unified are the
-- pop the context to remove the "Expected/Acutal" context
uTysOuter, uTys
- :: NoBoxes -> TcType -- ty1 is the *expected* type
- -> NoBoxes -> TcType -- ty2 is the *actual* type
- -> TcM ()
-uTysOuter nb1 ty1 nb2 ty2 = u_tys True nb1 ty1 ty1 nb2 ty2 ty2
-uTys nb1 ty1 nb2 ty2 = u_tys False nb1 ty1 ty1 nb2 ty2 ty2
+ :: InBox -> TcType -- ty1 is the *actual* type
+ -> InBox -> TcType -- ty2 is the *expected* type
+ -> TcM CoercionI
+uTysOuter nb1 ty1 nb2 ty2
+ = do { traceTc (text "uTysOuter" <+> ppr ty1 <+> ppr ty2)
+ ; u_tys True nb1 ty1 ty1 nb2 ty2 ty2 }
+uTys nb1 ty1 nb2 ty2
+ = do { traceTc (text "uTys" <+> ppr ty1 <+> ppr ty2)
+ ; u_tys False nb1 ty1 ty1 nb2 ty2 ty2 }
--------------
-uTys_s :: NoBoxes -> [TcType] -- ty1 is the *actual* types
- -> NoBoxes -> [TcType] -- ty2 is the *expected* types
- -> TcM ()
-uTys_s nb1 [] nb2 [] = returnM ()
-uTys_s nb1 (ty1:tys1) nb2 (ty2:tys2) = do { uTys nb1 ty1 nb2 ty2
- ; uTys_s nb1 tys1 nb2 tys2 }
+uTys_s :: InBox -> [TcType] -- tys1 are the *actual* types
+ -> InBox -> [TcType] -- tys2 are the *expected* types
+ -> TcM [CoercionI]
+uTys_s nb1 [] nb2 [] = returnM []
+uTys_s nb1 (ty1:tys1) nb2 (ty2:tys2) = do { coi <- uTys nb1 ty1 nb2 ty2
+ ; cois <- uTys_s nb1 tys1 nb2 tys2
+ ; return (coi:cois)
+ }
uTys_s nb1 ty1s nb2 ty2s = panic "Unify.uTys_s: mismatched type lists!"
--------------
u_tys :: Outer
- -> NoBoxes -> TcType -> TcType -- ty1 is the *actual* type
- -> NoBoxes -> TcType -> TcType -- ty2 is the *expected* type
- -> TcM ()
+ -> InBox -> TcType -> TcType -- ty1 is the *actual* type
+ -> InBox -> TcType -> TcType -- ty2 is the *expected* type
+ -> TcM CoercionI
u_tys outer nb1 orig_ty1 ty1 nb2 orig_ty2 ty2
- = go outer ty1 ty2
+ = do { traceTc (text "u_tys " <+> ppr ty1 <+> text " " <+> ppr ty2)
+ ; coi <- go outer ty1 ty2
+ ; traceTc (case coi of
+ ACo co -> text "u_tys yields coercion: " <+> ppr co
+ IdCo -> text "u_tys yields no coercion")
+ ; return coi
+ }
where
- -- Always expand synonyms (see notes at end)
+ go :: Outer -> TcType -> TcType -> TcM CoercionI
+ go outer ty1 ty2 =
+ do { traceTc (text "go " <+> ppr orig_ty1 <+> text "/" <+> ppr ty1
+ <+> ppr orig_ty2 <+> text "/" <+> ppr ty2)
+ ; go1 outer ty1 ty2
+ }
+
+ go1 :: Outer -> TcType -> TcType -> TcM CoercionI
+ -- Always expand synonyms: see Note [Unification and synonyms]
-- (this also throws away FTVs)
- go outer ty1 ty2
+ go1 outer ty1 ty2
| Just ty1' <- tcView ty1 = go False ty1' ty2
| Just ty2' <- tcView ty2 = go False ty1 ty2'
-- Variables; go for uVar
- go outer (TyVarTy tyvar1) ty2 = uVar outer False tyvar1 nb2 orig_ty2 ty2
- go outer ty1 (TyVarTy tyvar2) = uVar outer True tyvar2 nb1 orig_ty1 ty1
+ go1 outer (TyVarTy tyvar1) ty2 = uVar outer False tyvar1 nb2 orig_ty2 ty2
+ go1 outer ty1 (TyVarTy tyvar2) = uVar outer True tyvar2 nb1 orig_ty1 ty1
-- "True" means args swapped
+
+ -- The case for sigma-types must *follow* the variable cases
+ -- because a boxy variable can be filed with a polytype;
+ -- but must precede FunTy, because ((?x::Int) => ty) look
+ -- like a FunTy; there isn't necy a forall at the top
+ go1 _ ty1 ty2
+ | isSigmaTy ty1 || isSigmaTy ty2
+ = do { traceTc (text "We have sigma types: equalLength" <+> ppr tvs1 <+> ppr tvs2)
+ ; checkM (equalLength tvs1 tvs2)
+ (unifyMisMatch outer False orig_ty1 orig_ty2)
+ ; traceTc (text "We're past the first length test")
+ ; tvs <- tcInstSkolTyVars UnkSkol tvs1 -- Not a helpful SkolemInfo
+ -- Get location from monad, not from tvs1
+ ; let tys = mkTyVarTys tvs
+ in_scope = mkInScopeSet (mkVarSet tvs)
+ phi1 = substTy (mkTvSubst in_scope (zipTyEnv tvs1 tys)) body1
+ phi2 = substTy (mkTvSubst in_scope (zipTyEnv tvs2 tys)) body2
+ (theta1,tau1) = tcSplitPhiTy phi1
+ (theta2,tau2) = tcSplitPhiTy phi2
+
+ ; addErrCtxtM (unifyForAllCtxt tvs phi1 phi2) $ do
+ { checkM (equalLength theta1 theta2)
+ (unifyMisMatch outer False orig_ty1 orig_ty2)
+
+ ; cois <- uPreds False nb1 theta1 nb2 theta2 -- TOMDO: do something with these pred_cois
+ ; traceTc (text "TOMDO!")
+ ; coi <- uTys nb1 tau1 nb2 tau2
+
+ -- Check for escape; e.g. (forall a. a->b) ~ (forall a. a->a)
+ ; free_tvs <- zonkTcTyVarsAndFV (varSetElems (tyVarsOfType ty1 `unionVarSet` tyVarsOfType ty2))
+ ; ifM (any (`elemVarSet` free_tvs) tvs)
+ (bleatEscapedTvs free_tvs tvs tvs)
+
+ -- If both sides are inside a box, we are in a "box-meets-box"
+ -- situation, and we should not have a polytype at all.
+ -- If we get here we have two boxes, already filled with
+ -- the same polytype... but it should be a monotype.
+ -- This check comes last, because the error message is
+ -- extremely unhelpful.
+ ; ifM (nb1 && nb2) (notMonoType ty1)
+ ; return coi
+ }}
+ where
+ (tvs1, body1) = tcSplitForAllTys ty1
+ (tvs2, body2) = tcSplitForAllTys ty2
+
-- Predicates
- go outer (PredTy p1) (PredTy p2) = uPred outer nb1 p1 nb2 p2
+ go1 outer (PredTy p1) (PredTy p2)
+ = uPred False nb1 p1 nb2 p2
-- Type constructors must match
- go _ (TyConApp con1 tys1) (TyConApp con2 tys2)
- | con1 == con2 = uTys_s nb1 tys1 nb2 tys2
+ go1 _ (TyConApp con1 tys1) (TyConApp con2 tys2)
+ | con1 == con2 && not (isOpenSynTyCon con1)
+ = do { cois <- uTys_s nb1 tys1 nb2 tys2
+ ; return $ mkTyConAppCoI con1 tys1 cois
+ }
-- See Note [TyCon app]
+ | con1 == con2 && identicalOpenSynTyConApp
+ = do { cois <- uTys_s nb1 tys1' nb2 tys2'
+ ; return $ mkTyConAppCoI con1 tys1 (replicate n IdCo ++ cois)
+ }
+ where
+ n = tyConArity con1
+ (idxTys1, tys1') = splitAt n tys1
+ (idxTys2, tys2') = splitAt n tys2
+ identicalOpenSynTyConApp = idxTys1 `tcEqTypes` idxTys2
+ -- See Note [OpenSynTyCon app]
-- Functions; just check the two parts
- go _ (FunTy fun1 arg1) (FunTy fun2 arg2)
- = do { uTys nb1 fun1 nb2 fun2
- ; uTys nb1 arg1 nb2 arg2 }
+ go1 _ (FunTy fun1 arg1) (FunTy fun2 arg2)
+ = do { coi_l <- uTys nb1 fun1 nb2 fun2
+ ; coi_r <- uTys nb1 arg1 nb2 arg2
+ ; return $ mkFunTyCoI fun1 coi_l arg1 coi_r
+ }
-- Applications need a bit of care!
-- They can match FunTy and TyConApp, so use splitAppTy_maybe
-- NB: we've already dealt with type variables and Notes,
-- so if one type is an App the other one jolly well better be too
- go outer (AppTy s1 t1) ty2
+ go1 outer (AppTy s1 t1) ty2
| Just (s2,t2) <- tcSplitAppTy_maybe ty2
- = do { uTys nb1 s1 nb2 s2; uTys nb1 t1 nb2 t2 }
+ = do { coi_s <- uTys nb1 s1 nb2 s2; coi_t <- uTys nb1 t1 nb2 t2
+ ; return $ mkAppTyCoI s1 coi_s t1 coi_t }
-- Now the same, but the other way round
-- Don't swap the types, because the error messages get worse
- go outer ty1 (AppTy s2 t2)
+ go1 outer ty1 (AppTy s2 t2)
| Just (s1,t1) <- tcSplitAppTy_maybe ty1
- = do { uTys nb1 s1 nb2 s2; uTys nb1 t1 nb2 t2 }
-
- go _ ty1@(ForAllTy _ _) ty2@(ForAllTy _ _)
- | length tvs1 == length tvs2
- = do { tvs <- tcInstSkolTyVars UnkSkol tvs1 -- Not a helpful SkolemInfo
- ; let tys = mkTyVarTys tvs
- in_scope = mkInScopeSet (mkVarSet tvs)
- subst1 = mkTvSubst in_scope (zipTyEnv tvs1 tys)
- subst2 = mkTvSubst in_scope (zipTyEnv tvs2 tys)
- ; uTys nb1 (substTy subst1 body1) nb2 (substTy subst2 body2)
+ = do { coi_s <- uTys nb1 s1 nb2 s2; coi_t <- uTys nb1 t1 nb2 t2
+ ; return $ mkAppTyCoI s1 coi_s t1 coi_t }
+
+ -- One or both outermost constructors are type family applications.
+ -- If we can normalise them away, proceed as usual; otherwise, we
+ -- 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
+ else return (IdCo, ty1)
+ ; (coi2, ty2') <- if ty2_is_fun then tcNormalizeFamInst ty2
+ else return (IdCo, ty2)
+ ; coi <- if isOpenSynTyConApp ty1' || isOpenSynTyConApp ty2'
+ then do { -- One type family app can't be reduced yet
+ -- => defer
+ ; ty1'' <- zonkTcType ty1'
+ ; ty2'' <- zonkTcType ty2'
+ ; if tcEqType ty1'' ty2''
+ then return IdCo
+ else -- see [Deferred Unification]
+ defer_unification outer False orig_ty1 orig_ty2
+ }
+ else -- unification can proceed
+ go outer ty1' ty2'
+ ; return $ coi1 `mkTransCoI` coi `mkTransCoI` (mkSymCoI coi2)
+ }
+ where
+ ty1_is_fun = isOpenSynTyConApp ty1
+ ty2_is_fun = isOpenSynTyConApp ty2
- -- If both sides are inside a box, we should not have
- -- a polytype at all. This check comes last, because
- -- the error message is extremely unhelpful.
- ; ifM (nb1 && nb2) (notMonoType ty1)
- }
- where
- (tvs1, body1) = tcSplitForAllTys ty1
- (tvs2, body2) = tcSplitForAllTys ty2
+ -- Anything else fails
+ go1 outer _ _ = unifyMisMatch outer False orig_ty1 orig_ty2
- -- Anything else fails
- go outer _ _ = unifyMisMatch outer False orig_ty1 orig_ty2
----------
uPred outer nb1 (IParam n1 t1) nb2 (IParam n2 t2)
- | n1 == n2 = uTys nb1 t1 nb2 t2
+ | n1 == n2 =
+ do { coi <- uTys nb1 t1 nb2 t2
+ ; return $ mkIParamPredCoI n1 coi
+ }
uPred outer nb1 (ClassP c1 tys1) nb2 (ClassP c2 tys2)
- | c1 == c2 = uTys_s nb1 tys1 nb2 tys2 -- Guaranteed equal lengths because the kinds check
+ | c1 == c2 =
+ do { cois <- uTys_s nb1 tys1 nb2 tys2 -- Guaranteed equal lengths because the kinds check
+ ; return $ mkClassPPredCoI c1 tys1 cois
+ }
uPred outer _ p1 _ p2 = unifyMisMatch outer False (mkPredTy p1) (mkPredTy p2)
+
+uPreds outer nb1 [] nb2 [] = return []
+uPreds outer nb1 (p1:ps1) nb2 (p2:ps2) =
+ do { coi <- uPred outer nb1 p1 nb2 p2
+ ; cois <- uPreds outer nb1 ps1 nb2 ps2
+ ; return (coi:cois)
+ }
+uPreds outer nb1 ps1 nb2 ps2 = panic "uPreds"
\end{code}
-Note [Tycon app]
+Note [TyCon app]
~~~~~~~~~~~~~~~~
When we find two TyConApps, the argument lists are guaranteed equal
length. Reason: intially the kinds of the two types to be unified is
which we do, that ensures that f1,f2 have the same kind; and that
means a1,a2 have the same kind. And now the argument repeats.
+Note [OpenSynTyCon app]
+~~~~~~~~~~~~~~~~~~~~~~~
+Given
+
+ type family T a :: * -> *
+
+the two types (T () a) and (T () Int) must unify, even if there are
+no type instances for T at all. Should we just turn them into an
+equality (T () a ~ T () Int)? I don't think so. We currently try to
+eagerly unify everything we can before generating equalities; otherwise,
+we could turn the unification of [Int] with [a] into an equality, too.
-Notes on synonyms
-~~~~~~~~~~~~~~~~~
+Note [Unification and synonyms]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If you are tempted to make a short cut on synonyms, as in this
pseudocode...
\begin{code}
uVar :: Outer
- -> Bool -- False => tyvar is the "expected"
- -- True => ty is the "expected" thing
+ -> SwapFlag -- False => tyvar is the "actual" (ty is "expected")
+ -- True => ty is the "actual" (tyvar is "expected")
-> TcTyVar
- -> NoBoxes -- True <=> definitely no boxes in t2
+ -> InBox -- True <=> definitely no boxes in t2
-> TcTauType -> TcTauType -- printing and real versions
- -> TcM ()
+ -> TcM CoercionI
uVar outer swapped tv1 nb2 ps_ty2 ty2
= do { let expansion | showSDoc (ppr ty2) == showSDoc (ppr ps_ty2) = empty
| otherwise = brackets (equals <+> ppr ty2)
; traceTc (text "uVar" <+> ppr swapped <+>
sep [ppr tv1 <+> dcolon <+> ppr (tyVarKind tv1 ),
- nest 2 (ptext SLIT(" :=: ")),
+ nest 2 (ptext SLIT(" <-> ")),
ppr ps_ty2 <+> dcolon <+> ppr (typeKind ty2) <+> expansion])
; details <- lookupTcTyVar tv1
; case details of
IndirectTv ty1
| swapped -> u_tys outer nb2 ps_ty2 ty2 True ty1 ty1 -- Swap back
| otherwise -> u_tys outer True ty1 ty1 nb2 ps_ty2 ty2 -- Same order
- -- The 'True' here says that ty1
- -- is definitely box-free
- DoneTv details1 -> uUnfilledVar outer swapped tv1 details1 nb2 ps_ty2 ty2
+ -- The 'True' here says that ty1 is now inside a box
+ DoneTv details1 -> uUnfilledVar outer swapped tv1 details1 ps_ty2 ty2
}
----------------
uUnfilledVar :: Outer
- -> Bool -- Args are swapped
- -> TcTyVar -> TcTyVarDetails -- Tyvar 1
- -> NoBoxes -> TcTauType -> TcTauType -- Type 2
- -> TcM ()
+ -> SwapFlag
+ -> TcTyVar -> TcTyVarDetails -- Tyvar 1
+ -> TcTauType -> TcTauType -- Type 2
+ -> TcM CoercionI
-- Invariant: tyvar 1 is not unified with anything
-uUnfilledVar outer swapped tv1 details1 nb2 ps_ty2 ty2
+uUnfilledVar outer swapped tv1 details1 ps_ty2 ty2
| Just ty2' <- tcView ty2
= -- Expand synonyms; ignore FTVs
- uUnfilledVar False swapped tv1 details1 nb2 ps_ty2 ty2'
+ uUnfilledVar False swapped tv1 details1 ps_ty2 ty2'
-uUnfilledVar outer swapped tv1 details1 nb2 ps_ty2 (TyVarTy tv2)
+uUnfilledVar outer swapped tv1 details1 ps_ty2 (TyVarTy tv2)
| tv1 == tv2 -- Same type variable => no-op (but watch out for the boxy case)
= case details1 of
MetaTv BoxTv ref1 -- A boxy type variable meets itself;
-- this is box-meets-box, so fill in with a tau-type
-> do { tau_tv <- tcInstTyVar tv1
- ; updateMeta tv1 ref1 (mkTyVarTy tau_tv) }
- other -> returnM () -- No-op
+ ; updateMeta tv1 ref1 (mkTyVarTy tau_tv)
+ ; return IdCo
+ }
+ other -> returnM IdCo -- No-op
- -- Distinct type variables
- | otherwise
+ | otherwise -- Distinct type variables
= do { lookup2 <- lookupTcTyVar tv2
; case lookup2 of
- IndirectTv ty2' -> uUnfilledVar outer swapped tv1 details1 True ty2' ty2'
+ IndirectTv ty2' -> uUnfilledVar outer swapped tv1 details1 ty2' ty2'
DoneTv details2 -> uUnfilledVars outer swapped tv1 details1 tv2 details2
}
-uUnfilledVar outer swapped tv1 details1 nb2 ps_ty2 non_var_ty2 -- ty2 is not a type variable
- = case details1 of
- MetaTv (SigTv _) ref1 -> mis_match -- Can't update a skolem with a non-type-variable
- MetaTv info ref1 -> uMetaVar swapped tv1 info ref1 nb2 ps_ty2 non_var_ty2
- skolem_details -> mis_match
+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
where
- mis_match = unifyMisMatch outer swapped (TyVarTy tv1) ps_ty2
+ 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
+ ; case coi2 of
+ IdCo -> -- no progress, but maybe after other instantiations
+ defer_unification outer swapped (TyVarTy tv1) ps_ty2
+ ACo co -> -- progress: so lets try again
+ do { traceTc $
+ ppr co <+> text "::"<+> ppr non_var_ty2 <+> text "~" <+>
+ ppr ty2'
+ ; coi <- uUnfilledVar outer swapped tv1 details1 ps_ty2 ty2'
+ ; let coi2' = (if swapped then id else mkSymCoI) coi2
+ ; return $ coi2' `mkTransCoI` coi
+ }
+ }
+ | SkolemTv RuntimeUnkSkol <- details1
+ -- runtime unknown will never match
+ = unifyMisMatch outer swapped (TyVarTy tv1) ps_ty2
+ | otherwise -- defer as a given equality may still resolve this
+ = defer_unification outer swapped (TyVarTy tv1) ps_ty2
+\end{code}
+
+Note [Deferred Unification]
+~~~~~~~~~~~~~~~~~~~~
+We may encounter a unification ty1 = ty2 that cannot be performed syntactically,
+and yet its consistency is undetermined. Previously, there was no way to still
+make it consistent. So a mismatch error was issued.
+
+Now these unfications are deferred until constraint simplification, where type
+family instances and given equations may (or may not) establish the consistency.
+Deferred unifications are of the form
+ F ... ~ ...
+or x ~ ...
+where F is a type function and x is a type variable.
+E.g.
+ id :: x ~ y => x -> y
+ id e = e
+
+involves the unfication x = y. It is deferred until we bring into account the
+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
+improve error messages.
+
+\begin{code}
+defer_unification :: Bool -- pop innermost context?
+ -> SwapFlag
+ -> TcType
+ -> TcType
+ -> TcM CoercionI
+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
+ ; traceTc $ text "deferring:" <+> ppr ty1 <+> text "~" <+> ppr ty2
+ ; cotv <- newMetaTyVar TauTv (mkCoKind ty1' ty2')
+ -- put ty1 ~ ty2 in LIE
+ -- Left means "wanted"
+ ; inst <- (if outer then popErrCtxt else id) $
+ mkEqInst (EqPred ty1' ty2') (Left cotv)
+ ; extendLIE inst
+ ; return $ ACo $ TyVarTy cotv }
----------------
-uMetaVar :: Bool
+uMetaVar :: SwapFlag
-> TcTyVar -> BoxInfo -> IORef MetaDetails
- -> NoBoxes -> TcType -> TcType
+ -> TcType -> TcType
-> TcM ()
-- tv1 is an un-filled-in meta type variable (maybe boxy, maybe tau)
-- ty2 is not a type variable
-uMetaVar swapped tv1 BoxTv ref1 nb2 ps_ty2 non_var_ty2
+uMetaVar 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
--
; case meta_details of
Indirect ty -> WARN( True, ppr tv1 <+> ppr ty )
return () -- This really should *not* happen
- Flexi -> return ()
+ Flexi -> return ()
#endif
; checkUpdateMeta swapped tv1 ref1 final_ty }
-uMetaVar swapped tv1 info1 ref1 nb2 ps_ty2 non_var_ty2
+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 }
----------------
uUnfilledVars :: Outer
- -> Bool -- Args are swapped
+ -> SwapFlag
-> TcTyVar -> TcTyVarDetails -- Tyvar 1
-> TcTyVar -> TcTyVarDetails -- Tyvar 2
- -> TcM ()
+ -> TcM CoercionI
-- Invarant: The type variables are distinct,
-- Neither is filled in yet
-- They might be boxy or not
uUnfilledVars outer swapped tv1 (SkolemTv _) tv2 (SkolemTv _)
- = unifyMisMatch outer swapped (mkTyVarTy tv1) (mkTyVarTy tv2)
+ = -- see [Deferred Unification]
+ defer_unification outer swapped (mkTyVarTy tv1) (mkTyVarTy tv2)
uUnfilledVars outer swapped tv1 (MetaTv info1 ref1) tv2 (SkolemTv _)
- = checkUpdateMeta swapped tv1 ref1 (mkTyVarTy tv2)
+ = checkUpdateMeta swapped tv1 ref1 (mkTyVarTy tv2) >> return IdCo
uUnfilledVars outer swapped tv1 (SkolemTv _) tv2 (MetaTv info2 ref2)
- = checkUpdateMeta (not swapped) tv2 ref2 (mkTyVarTy tv1)
+ = checkUpdateMeta (not swapped) tv2 ref2 (mkTyVarTy tv1) >> return IdCo
-- ToDo: this function seems too long for what it acutally does!
uUnfilledVars outer swapped tv1 (MetaTv info1 ref1) tv2 (MetaTv info2 ref2)
= case (info1, info2) of
- (BoxTv, BoxTv) -> box_meets_box
+ (BoxTv, BoxTv) -> box_meets_box >> return IdCo
-- If a box meets a TauTv, but the fomer has the smaller kind
-- then we must create a fresh TauTv with the smaller kind
- (_, BoxTv) | k1_sub_k2 -> update_tv2
- | otherwise -> box_meets_box
- (BoxTv, _ ) | k2_sub_k1 -> update_tv1
- | otherwise -> box_meets_box
+ (_, BoxTv) | k1_sub_k2 -> update_tv2 >> return IdCo
+ | otherwise -> box_meets_box >> return IdCo
+ (BoxTv, _ ) | k2_sub_k1 -> update_tv1 >> return IdCo
+ | otherwise -> box_meets_box >> return IdCo
-- Avoid SigTvs if poss
- (SigTv _, _ ) | k1_sub_k2 -> update_tv2
- (_, SigTv _) | k2_sub_k1 -> update_tv1
+ (SigTv _, _ ) | k1_sub_k2 -> update_tv2 >> return IdCo
+ (_, SigTv _) | k2_sub_k1 -> update_tv1 >> return IdCo
(_, _) | k1_sub_k2 -> if k2_sub_k1 && nicer_to_update_tv1
- then update_tv1 -- Same kinds
- else update_tv2
- | k2_sub_k1 -> update_tv1
- | otherwise -> kind_err
+ then update_tv1 >> return IdCo -- Same kinds
+ else update_tv2 >> return IdCo
+ | k2_sub_k1 -> update_tv1 >> return IdCo
+ | otherwise -> kind_err >> return IdCo
-- Update the variable with least kind info
-- See notes on type inference in Kind.lhs
k1_sub_k2 = k1 `isSubKind` k2
k2_sub_k1 = k2 `isSubKind` k1
- nicer_to_update_tv1 = isSystemName (varName tv1)
+ nicer_to_update_tv1 = isSystemName (Var.varName tv1)
-- 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 :: Bool -> TcTyVar -> IORef MetaDetails -> TcType -> TcM ()
+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)
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) }
+ ; writeMutVar ref1 (Indirect ty2)
+ }
----------------
checkKinds swapped tv1 ty2
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)
; case mb_tys' of
Just tys' -> return (TyConApp tc tys')
-- Retain the synonym (the common case)
- Nothing -> go (expectJust "checkTauTvUpdate"
+ 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
}
Rather, we should bind t to () (= non_var_ty2).
\begin{code}
-stripBoxyType :: BoxyType -> TcM TcType
--- Strip all boxes from the input type, returning a non-boxy type.
--- It's fine for there to be a polytype inside a box (c.f. unBox)
--- All of the boxes should have been filled in by now;
--- hence we return a TcType
-stripBoxyType ty = zonkType strip_tv ty
- where
- strip_tv tv = ASSERT( not (isBoxyTyVar tv) ) return (TyVarTy tv)
- -- strip_tv will be called for *Flexi* meta-tyvars
- -- There should not be any Boxy ones; hence the ASSERT
+refineBox :: TcType -> TcM TcType
+-- Unbox the outer box of a boxy type (if any)
+refineBox ty@(TyVarTy box_tv)
+ | isMetaTyVar box_tv
+ = do { cts <- readMetaTyVar box_tv
+ ; case cts of
+ Flexi -> return ty
+ Indirect ty -> return ty }
+refineBox other_ty = return other_ty
+
+refineBoxToTau :: TcType -> TcM TcType
+-- Unbox the outer box of a boxy type, filling with a monotype if it is empty
+-- Like refineBox except for the "fill with monotype" part.
+refineBoxToTau ty@(TyVarTy box_tv)
+ | isMetaTyVar box_tv
+ , MetaTv BoxTv ref <- tcTyVarDetails box_tv
+ = do { cts <- readMutVar ref
+ ; case cts of
+ Flexi -> fillBoxWithTau box_tv ref
+ Indirect ty -> return ty }
+refineBoxToTau other_ty = return other_ty
zapToMonotype :: BoxySigmaType -> TcM TcTauType
-- Subtle... we must zap the boxy res_ty
, MetaTv BoxTv ref <- tcTyVarDetails tv -- NB: non-TcTyVars are possible
= do { cts <- readMutVar ref -- under nested quantifiers
; case cts of
- Flexi -> fillBoxWithTau tv ref
+ Flexi -> fillBoxWithTau tv ref
Indirect ty -> do { non_boxy_ty <- unBox ty
; if isTauTy non_boxy_ty
then return non_boxy_ty
unBoxPred (ClassP cls tys) = do { tys' <- mapM unBox tys; return (ClassP cls tys') }
unBoxPred (IParam ip ty) = do { ty' <- unBox ty; return (IParam ip ty') }
+unBoxPred (EqPred ty1 ty2) = do { ty1' <- unBox ty1; ty2' <- unBox ty2; return (EqPred ty1' ty2') }
\end{code}
----------------
-- If an error happens we try to figure out whether the function
-- function has been given too many or too few arguments, and say so.
-checkFunResCtxt fun actual_res_ty expected_res_ty tidy_env
- = do { exp_ty' <- zonkTcType expected_res_ty
- ; act_ty' <- zonkTcType actual_res_ty
- ; let
- (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
- (env2, act_ty'') = tidyOpenType env1 act_ty'
- (exp_args, _) = tcSplitFunTys exp_ty''
- (act_args, _) = tcSplitFunTys act_ty''
+addSubCtxt SubDone actual_res_ty expected_res_ty thing_inside
+ = thing_inside
+addSubCtxt sub_ctxt actual_res_ty expected_res_ty thing_inside
+ = addErrCtxtM mk_err thing_inside
+ where
+ mk_err tidy_env
+ = do { exp_ty' <- zonkTcType expected_res_ty
+ ; act_ty' <- zonkTcType actual_res_ty
+ ; let (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
+ (env2, act_ty'') = tidyOpenType env1 act_ty'
+ (exp_args, _) = tcSplitFunTys exp_ty''
+ (act_args, _) = tcSplitFunTys act_ty''
- len_act_args = length act_args
- len_exp_args = length exp_args
+ len_act_args = length act_args
+ len_exp_args = length exp_args
- message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun
- | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun
- | otherwise = mkExpectedActualMsg act_ty'' exp_ty''
- ; return (env2, message) }
+ message = case sub_ctxt of
+ SubFun fun | len_exp_args < len_act_args -> wrongArgsCtxt "too few" fun
+ | len_exp_args > len_act_args -> wrongArgsCtxt "too many" fun
+ other -> mkExpectedActualMsg act_ty'' exp_ty''
+ ; return (env2, message) }
- where
wrongArgsCtxt too_many_or_few fun
= ptext SLIT("Probable cause:") <+> quotes (ppr fun)
<+> ptext SLIT("is applied to") <+> text too_many_or_few
<+> ptext SLIT("arguments")
------------------
+unifyForAllCtxt tvs phi1 phi2 env
+ = returnM (env2, msg)
+ where
+ (env', tvs') = tidyOpenTyVars env tvs -- NB: not tidyTyVarBndrs
+ (env1, phi1') = tidyOpenType env' phi1
+ (env2, phi2') = tidyOpenType env1 phi2
+ 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
pp2 = ppr ty2' <+> dcolon <+> ppr (typeKind ty2)
unifyMisMatch outer swapped ty1 ty2
- = do { (env, msg) <- if swapped then misMatchMsg ty1 ty2
- else misMatchMsg ty2 ty1
+ = do { (env, msg) <- if swapped then misMatchMsg ty2 ty1
+ else misMatchMsg ty1 ty2
-- This is the whole point of the 'outer' stuff
; if outer then popErrCtxt (failWithTcM (env, msg))
else failWithTcM (env, msg)
}
-misMatchMsg ty1 ty2
- = do { env0 <- tcInitTidyEnv
- ; (env1, pp1, extra1) <- ppr_ty env0 ty1
- ; (env2, pp2, extra2) <- ppr_ty env1 ty2
- ; return (env2, sep [sep [ptext SLIT("Couldn't match expected type") <+> pp1,
- nest 7 (ptext SLIT("against inferred type") <+> pp2)],
- nest 2 extra1, nest 2 extra2]) }
-
-ppr_ty :: TidyEnv -> TcType -> TcM (TidyEnv, SDoc, SDoc)
-ppr_ty env ty
- = do { ty' <- zonkTcType ty
- ; let (env1,tidy_ty) = tidyOpenType env ty'
- simple_result = (env1, quotes (ppr tidy_ty), empty)
- ; case tidy_ty of
- TyVarTy tv
- | isSkolemTyVar tv -> return (env2, pp_rigid tv',
- pprSkolTvBinding tv')
- | otherwise -> return simple_result
- where
- (env2, tv') = tidySkolemTyVar env1 tv
- other -> return simple_result }
- where
- pp_rigid tv = quotes (ppr tv) <+> parens (ptext SLIT("a rigid variable"))
-
-
+-----------------------
notMonoType ty
= do { ty' <- zonkTcType ty
; env0 <- tcInitTidyEnv
; let (env1, tidy_ty) = tidyOpenType env0 ty'
- msg = ptext SLIT("Cannot match a monotype with") <+> ppr tidy_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
unifyKind :: TcKind -- Expected
-> TcKind -- Actual
-> TcM ()
-unifyKind LiftedTypeKind LiftedTypeKind = returnM ()
-unifyKind UnliftedTypeKind UnliftedTypeKind = returnM ()
+unifyKind (TyConApp kc1 []) (TyConApp kc2 [])
+ | isSubKindCon kc2 kc1 = returnM ()
-unifyKind OpenTypeKind k2 | isOpenTypeKind k2 = returnM ()
-unifyKind ArgTypeKind k2 | isArgTypeKind k2 = returnM ()
- -- Respect sub-kinding
-
-unifyKind (FunKind a1 r1) (FunKind a2 r2)
- = do { unifyKind a2 a1; unifyKind r1 r2 }
+unifyKind (FunTy a1 r1) (FunTy a2 r2)
+ = do { unifyKind a2 a1; unifyKind r1 r2 }
-- Notice the flip in the argument,
-- so that the sub-kinding works right
-
-unifyKind (KindVar kv1) k2 = uKVar False kv1 k2
-unifyKind k1 (KindVar kv2) = uKVar True kv2 k1
+unifyKind (TyVarTy kv1) k2 = uKVar False kv1 k2
+unifyKind k1 (TyVarTy kv2) = uKVar True kv2 k1
unifyKind k1 k2 = unifyKindMisMatch k1 k2
unifyKinds :: [TcKind] -> [TcKind] -> TcM ()
uKVar swapped kv1 k2
= do { mb_k1 <- readKindVar kv1
; case mb_k1 of
- Nothing -> uUnboundKVar swapped kv1 k2
- Just k1 | swapped -> unifyKind k2 k1
- | otherwise -> unifyKind k1 k2 }
+ Flexi -> uUnboundKVar swapped kv1 k2
+ Indirect k1 | swapped -> unifyKind k2 k1
+ | otherwise -> unifyKind k1 k2 }
----------------
uUnboundKVar :: Bool -> KindVar -> TcKind -> TcM ()
-uUnboundKVar swapped kv1 k2@(KindVar kv2)
+uUnboundKVar swapped kv1 k2@(TyVarTy kv2)
| kv1 == kv2 = returnM ()
| otherwise -- Distinct kind variables
= do { mb_k2 <- readKindVar kv2
; case mb_k2 of
- Just k2 -> uUnboundKVar swapped kv1 k2
- Nothing -> writeKindVar kv1 k2 }
+ Indirect k2 -> uUnboundKVar swapped kv1 k2
+ Flexi -> writeKindVar kv1 k2 }
uUnboundKVar swapped kv1 non_var_k2
= do { k2' <- zonkTcKind non_var_k2
kindOccurCheck kv1 k2 -- k2 is zonked
= checkTc (not_in k2) (kindOccurCheckErr kv1 k2)
where
- not_in (KindVar kv2) = kv1 /= kv2
- not_in (FunKind a2 r2) = not_in a2 && not_in r2
- not_in other = True
+ not_in (TyVarTy kv2) = kv1 /= kv2
+ not_in (FunTy a2 r2) = not_in a2 && not_in r2
+ not_in other = True
kindSimpleKind :: Bool -> Kind -> TcM SimpleKind
-- (kindSimpleKind True k) returns a simple kind sk such that sk <: k
kindSimpleKind orig_swapped orig_kind
= go orig_swapped orig_kind
where
- go sw (FunKind k1 k2) = do { k1' <- go (not sw) k1
- ; k2' <- go sw k2
- ; return (FunKind k1' k2') }
- go True OpenTypeKind = return liftedTypeKind
- go True ArgTypeKind = return liftedTypeKind
- go sw LiftedTypeKind = return liftedTypeKind
- go sw UnliftedTypeKind = return unliftedTypeKind
- go sw k@(KindVar _) = return k -- KindVars are always simple
+ go sw (FunTy k1 k2) = do { k1' <- go (not sw) k1
+ ; k2' <- go sw k2
+ ; return (mkArrowKind k1' k2') }
+ go True k
+ | isOpenTypeKind k = return liftedTypeKind
+ | isArgTypeKind k = return liftedTypeKind
+ go sw k
+ | isLiftedTypeKind k = return liftedTypeKind
+ | isUnliftedTypeKind k = return unliftedTypeKind
+ go sw k@(TyVarTy _) = return k -- KindVars are always simple
go swapped kind = failWithTc (ptext SLIT("Unexpected kind unification failure:")
<+> ppr orig_swapped <+> ppr orig_kind)
-- I think this can't actually happen
unifyFunKind :: TcKind -> TcM (Maybe (TcKind, TcKind))
-- Like unifyFunTy, but does not fail; instead just returns Nothing
-unifyFunKind (KindVar kvar)
- = readKindVar kvar `thenM` \ maybe_kind ->
+unifyFunKind (TyVarTy kvar)
+ = readKindVar kvar `thenM` \ maybe_kind ->
case maybe_kind of
- Just fun_kind -> unifyFunKind fun_kind
- Nothing -> do { arg_kind <- newKindVar
- ; res_kind <- newKindVar
- ; writeKindVar kvar (mkArrowKind arg_kind res_kind)
- ; returnM (Just (arg_kind,res_kind)) }
+ Indirect fun_kind -> unifyFunKind fun_kind
+ Flexi ->
+ do { arg_kind <- newKindVar
+ ; res_kind <- newKindVar
+ ; writeKindVar kvar (mkArrowKind arg_kind res_kind)
+ ; returnM (Just (arg_kind,res_kind)) }
-unifyFunKind (FunKind arg_kind res_kind) = returnM (Just (arg_kind,res_kind))
-unifyFunKind other = returnM Nothing
+unifyFunKind (FunTy arg_kind res_kind) = returnM (Just (arg_kind,res_kind))
+unifyFunKind other = returnM Nothing
\end{code}
%************************************************************************
checkExpectedKind :: Outputable a => a -> TcKind -> TcKind -> TcM ()
-- A fancy wrapper for 'unifyKind', which tries
-- to give decent error messages.
+-- (checkExpectedKind ty act_kind exp_kind)
+-- checks that the actual kind act_kind is compatible
+-- with the expected kind exp_kind
+-- The first argument, ty, is used only in the error message generation
checkExpectedKind ty act_kind exp_kind
| act_kind `isSubKind` exp_kind -- Short cut for a very common case
= returnM ()
projects / ghc-hetmet.git / blobdiff