%
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
-\section[Unify]{Unifier}
-
-The unifier is now squarely in the typechecker monad (because of the
-updatable substitution).
+\section{Type subsumption and unification}
\begin{code}
-module TcUnify ( unifyTauTy, unifyTauTyList, unifyTauTyLists,
- unifyFunTy, unifyListTy, unifyTupleTy,
- unifyKind, unifyKinds, unifyOpenTypeKind
- ) where
+module TcUnify (
+ -- Full-blown subsumption
+ tcSubOff, tcSubExp, tcGen, subFunTy, TcHoleType,
+ checkSigTyVars, checkSigTyVarsWrt, sigCtxt,
+
+ -- Various unifications
+ unifyTauTy, unifyTauTyList, unifyTauTyLists,
+ unifyFunTy, unifyListTy, unifyPArrTy, unifyTupleTy,
+ unifyKind, unifyKinds, unifyOpenTypeKind,
+
+ -- Coercions
+ Coercion, ExprCoFn, PatCoFn,
+ (<$>), (<.>), mkCoercion,
+ idCoercion, isIdCoercion
+
+ ) where
#include "HsVersions.h"
--- friends:
-import TcMonad
-import TypeRep ( Type(..), PredType(..) ) -- friend
-import Type ( funTyCon, Kind, unboxedTypeKind, boxedTypeKind, openTypeKind,
- superBoxity, typeCon, openKindCon, hasMoreBoxityInfo,
- tyVarsOfType, typeKind,
- mkTyVarTy, mkFunTy, splitFunTy_maybe, splitTyConApp_maybe,
- isNotUsgTy, splitAppTy_maybe, mkTyConApp,
- tidyOpenType, tidyOpenTypes, tidyTyVar
- )
-import TyCon ( TyCon, isTupleTyCon, tupleTyConBoxity, tyConArity )
-import Name ( hasBetterProv )
-import Var ( TyVar, tyVarKind, varName, isSigTyVar )
-import VarSet ( varSetElems )
-import TcType ( TcType, TcTauType, TcTyVar, TcKind, newBoxityVar,
- newTyVarTy, newTyVarTys, tcGetTyVar, tcPutTyVar, zonkTcType
- )
-
--- others:
-import BasicTypes ( Arity, Boxity, isBoxed )
-import TysWiredIn ( listTyCon, mkListTy, mkTupleTy )
+
+import HsSyn ( HsExpr(..) )
+import TcHsSyn ( TypecheckedHsExpr, TcPat, mkHsLet )
+import TypeRep ( Type(..), SourceType(..), TyNote(..),
+ openKindCon, typeCon )
+
+import TcMonad -- TcType, amongst others
+import TcType ( TcKind, TcType, TcSigmaType, TcRhoType, TcTyVar, TcTauType,
+ TcTyVarSet, TcThetaType, TyVarDetails(SigTv),
+ isTauTy, isSigmaTy,
+ tcSplitAppTy_maybe, tcSplitTyConApp_maybe,
+ tcGetTyVar_maybe, tcGetTyVar,
+ mkTyConApp, mkFunTy, tyVarsOfType, mkPhiTy,
+ typeKind, tcSplitFunTy_maybe, mkForAllTys,
+ isHoleTyVar, isSkolemTyVar, isUserTyVar,
+ tidyOpenType, tidyOpenTypes, tidyOpenTyVar, tidyOpenTyVars,
+ eqKind, openTypeKind, liftedTypeKind, isTypeKind,
+ hasMoreBoxityInfo, tyVarBindingInfo, allDistinctTyVars
+ )
+import qualified Type ( getTyVar_maybe )
+import Inst ( LIE, emptyLIE, plusLIE,
+ newDicts, instToId, tcInstCall
+ )
+import TcMType ( getTcTyVar, putTcTyVar, tcInstType, readHoleResult,
+ newTyVarTy, newTyVarTys, newBoxityVar, newHoleTyVarTy,
+ zonkTcType, zonkTcTyVars, zonkTcTyVarsAndFV, zonkTcTyVar )
+import TcSimplify ( tcSimplifyCheck )
+import TysWiredIn ( listTyCon, parrTyCon, mkListTy, mkPArrTy, mkTupleTy )
+import TcEnv ( TcTyThing(..), tcGetGlobalTyVars, tcLEnvElts )
+import TyCon ( tyConArity, isTupleTyCon, tupleTyConBoxity )
+import PprType ( pprType )
+import Id ( Id, mkSysLocal, idType )
+import Var ( Var, varName, tyVarKind )
+import VarSet ( emptyVarSet, unionVarSet, elemVarSet, varSetElems )
+import VarEnv
+import Name ( isSystemName, getSrcLoc )
+import ErrUtils ( Message )
+import BasicTypes ( Boxity, Arity, isBoxed )
+import Util ( equalLength )
+import Maybe ( isNothing )
import Outputable
\end{code}
+Notes on holes
+~~~~~~~~~~~~~~
+* A hole is always filled in with an ordinary type, not another hole.
%************************************************************************
%* *
-\subsection{The Kind variants}
+\subsection{Subsumption}
%* *
%************************************************************************
+All the tcSub calls have the form
+
+ tcSub expected_ty offered_ty
+which checks
+ offered_ty <= expected_ty
+
+That is, that a value of type offered_ty is acceptable in
+a place expecting a value of type expected_ty.
+
+It returns a coercion function
+ co_fn :: offered_ty -> expected_ty
+which takes an HsExpr of type offered_ty into one of type
+expected_ty.
+
\begin{code}
-unifyKind :: TcKind -- Expected
- -> TcKind -- Actual
- -> TcM ()
-unifyKind k1 k2
- = tcAddErrCtxtM (unifyCtxt "kind" k1 k2) $
- uTys k1 k1 k2 k2
+type TcHoleType = TcSigmaType -- Either a TcSigmaType,
+ -- or else a hole
-unifyKinds :: [TcKind] -> [TcKind] -> TcM ()
-unifyKinds [] [] = returnTc ()
-unifyKinds (k1:ks1) (k2:ks2) = unifyKind k1 k2 `thenTc_`
- unifyKinds ks1 ks2
-unifyKinds _ _ = panic "unifyKinds: length mis-match"
+tcSubExp :: TcHoleType -> TcSigmaType -> TcM (ExprCoFn, LIE)
+tcSubOff :: TcSigmaType -> TcHoleType -> TcM (ExprCoFn, LIE)
+tcSub :: TcSigmaType -> TcSigmaType -> TcM (ExprCoFn, LIE)
\end{code}
+These two check for holes
+
\begin{code}
-unifyOpenTypeKind :: TcKind -> TcM ()
--- Ensures that the argument kind is of the form (Type bx)
--- for some boxity bx
+tcSubExp expected_ty offered_ty
+ = checkHole expected_ty offered_ty tcSub
-unifyOpenTypeKind ty@(TyVarTy tyvar)
- = tcGetTyVar tyvar `thenNF_Tc` \ maybe_ty ->
+tcSubOff expected_ty offered_ty
+ = checkHole offered_ty expected_ty (\ off exp -> tcSub exp off)
+
+-- checkHole looks for a hole in its first arg;
+-- If so, and it is uninstantiated, it fills in the hole
+-- with its second arg
+-- Otherwise it calls thing_inside, passing the two args, looking
+-- through any instantiated hole
+
+checkHole (TyVarTy tv) other_ty thing_inside
+ | isHoleTyVar tv
+ = getTcTyVar tv `thenNF_Tc` \ maybe_ty ->
case maybe_ty of
- Just ty' -> unifyOpenTypeKind ty'
- other -> unify_open_kind_help ty
+ Just ty -> thing_inside ty other_ty
+ Nothing -> putTcTyVar tv other_ty `thenNF_Tc_`
+ returnTc (idCoercion, emptyLIE)
-unifyOpenTypeKind ty
- = case splitTyConApp_maybe ty of
- Just (tycon, [_]) | tycon == typeCon -> returnTc ()
- other -> unify_open_kind_help ty
+checkHole ty other_ty thing_inside
+ = thing_inside ty other_ty
+\end{code}
-unify_open_kind_help ty -- Revert to ordinary unification
- = newBoxityVar `thenNF_Tc` \ boxity ->
- unifyKind ty (mkTyConApp typeCon [boxity])
+No holes expected now. Add some error-check context info.
+
+\begin{code}
+tcSub expected_ty actual_ty
+ = traceTc (text "tcSub" <+> details) `thenNF_Tc_`
+ tcAddErrCtxtM (unifyCtxt "type" expected_ty actual_ty)
+ (tc_sub expected_ty expected_ty actual_ty actual_ty)
+ where
+ details = vcat [text "Expected:" <+> ppr expected_ty,
+ text "Actual: " <+> ppr actual_ty]
+\end{code}
+
+tc_sub carries the types before and after expanding type synonyms
+
+\begin{code}
+tc_sub :: TcSigmaType -- expected_ty, before expanding synonyms
+ -> TcSigmaType -- ..and after
+ -> TcSigmaType -- actual_ty, before
+ -> TcSigmaType -- ..and after
+ -> TcM (ExprCoFn, LIE)
+
+-----------------------------------
+-- Expand synonyms
+tc_sub exp_sty (NoteTy _ exp_ty) act_sty act_ty = tc_sub exp_sty exp_ty act_sty act_ty
+tc_sub exp_sty exp_ty act_sty (NoteTy _ act_ty) = tc_sub exp_sty exp_ty act_sty act_ty
+
+-----------------------------------
+-- Generalisation case
+-- actual_ty: d:Eq b => b->b
+-- expected_ty: forall a. Ord a => a->a
+-- co_fn e /\a. \d2:Ord a. let d = eqFromOrd d2 in e
+
+-- It is essential to do this *before* the specialisation case
+-- Example: f :: (Eq a => a->a) -> ...
+-- g :: Ord b => b->b
+-- Consider f g !
+
+tc_sub exp_sty expected_ty act_sty actual_ty
+ | isSigmaTy expected_ty
+ = tcGen expected_ty (tyVarsOfType actual_ty) (
+ -- It's really important to check for escape wrt the free vars of
+ -- both expected_ty *and* actual_ty
+ \ body_exp_ty -> tc_sub body_exp_ty body_exp_ty act_sty actual_ty
+ ) `thenTc` \ (gen_fn, co_fn, lie) ->
+ returnTc (gen_fn <.> co_fn, lie)
+
+-----------------------------------
+-- Specialisation case:
+-- actual_ty: forall a. Ord a => a->a
+-- expected_ty: Int -> Int
+-- co_fn e = e Int dOrdInt
+
+tc_sub exp_sty expected_ty act_sty actual_ty
+ | isSigmaTy actual_ty
+ = tcInstCall Rank2Origin actual_ty `thenNF_Tc` \ (inst_fn, lie1, body_ty) ->
+ tc_sub exp_sty expected_ty body_ty body_ty `thenTc` \ (co_fn, lie2) ->
+ returnTc (co_fn <.> mkCoercion inst_fn, lie1 `plusLIE` lie2)
+
+-----------------------------------
+-- Function case
+
+tc_sub _ (FunTy exp_arg exp_res) _ (FunTy act_arg act_res)
+ = tcSub_fun exp_arg exp_res act_arg act_res
+
+-----------------------------------
+-- Type variable meets function: imitate
+--
+-- NB 1: we can't just unify the type variable with the type
+-- because the type might not be a tau-type, and we aren't
+-- allowed to instantiate an ordinary type variable with
+-- a sigma-type
+--
+-- NB 2: can we short-cut to an error case?
+-- when the arg/res is not a tau-type?
+-- NO! e.g. f :: ((forall a. a->a) -> Int) -> Int
+-- then x = (f,f)
+-- is perfectly fine!
+
+tc_sub exp_sty exp_ty@(FunTy exp_arg exp_res) _ (TyVarTy tv)
+ = ASSERT( not (isHoleTyVar tv) )
+ getTcTyVar tv `thenNF_Tc` \ maybe_ty ->
+ case maybe_ty of
+ Just ty -> tc_sub exp_sty exp_ty ty ty
+ Nothing -> imitateFun tv exp_sty `thenNF_Tc` \ (act_arg, act_res) ->
+ tcSub_fun exp_arg exp_res act_arg act_res
+
+tc_sub _ (TyVarTy tv) act_sty act_ty@(FunTy act_arg act_res)
+ = ASSERT( not (isHoleTyVar tv) )
+ getTcTyVar tv `thenNF_Tc` \ maybe_ty ->
+ case maybe_ty of
+ Just ty -> tc_sub ty ty act_sty act_ty
+ Nothing -> imitateFun tv act_sty `thenNF_Tc` \ (exp_arg, exp_res) ->
+ tcSub_fun exp_arg exp_res act_arg act_res
+
+-----------------------------------
+-- Unification case
+-- If none of the above match, we revert to the plain unifier
+tc_sub exp_sty expected_ty act_sty actual_ty
+ = uTys exp_sty expected_ty act_sty actual_ty `thenTc_`
+ returnTc (idCoercion, emptyLIE)
+\end{code}
+
+%************************************************************************
+%* *
+\subsection{Functions}
+%* *
+%************************************************************************
+
+\begin{code}
+tcSub_fun exp_arg exp_res act_arg act_res
+ = tc_sub act_arg act_arg exp_arg exp_arg `thenTc` \ (co_fn_arg, lie1) ->
+ tc_sub exp_res exp_res act_res act_res `thenTc` \ (co_fn_res, lie2) ->
+ tcGetUnique `thenNF_Tc` \ uniq ->
+ let
+ -- co_fn_arg :: HsExpr exp_arg -> HsExpr act_arg
+ -- co_fn_res :: HsExpr act_res -> HsExpr exp_res
+ -- co_fn :: HsExpr (act_arg -> act_res) -> HsExpr (exp_arg -> exp_res)
+ arg_id = mkSysLocal FSLIT("sub") uniq exp_arg
+ coercion | isIdCoercion co_fn_arg,
+ isIdCoercion co_fn_res = idCoercion
+ | otherwise = mkCoercion co_fn
+
+ co_fn e = DictLam [arg_id]
+ (co_fn_res <$> (HsApp e (co_fn_arg <$> (HsVar arg_id))))
+ -- Slight hack; using a "DictLam" to get an ordinary simple lambda
+ -- HsVar arg_id :: HsExpr exp_arg
+ -- co_fn_arg $it :: HsExpr act_arg
+ -- HsApp e $it :: HsExpr act_res
+ -- co_fn_res $it :: HsExpr exp_res
+ in
+ returnTc (coercion, lie1 `plusLIE` lie2)
+
+imitateFun :: TcTyVar -> TcType -> NF_TcM (TcType, TcType)
+imitateFun tv ty
+ = ASSERT( not (isHoleTyVar tv) )
+ -- NB: tv is an *ordinary* tyvar and so are the new ones
+
+ -- Check that tv isn't a type-signature type variable
+ -- (This would be found later in checkSigTyVars, but
+ -- we get a better error message if we do it here.)
+ checkTcM (not (isSkolemTyVar tv))
+ (failWithTcM (unifyWithSigErr tv ty)) `thenTc_`
+
+ newTyVarTy openTypeKind `thenNF_Tc` \ arg ->
+ newTyVarTy openTypeKind `thenNF_Tc` \ res ->
+ putTcTyVar tv (mkFunTy arg res) `thenNF_Tc_`
+ returnNF_Tc (arg,res)
\end{code}
%************************************************************************
%* *
+\subsection{Generalisation}
+%* *
+%************************************************************************
+
+\begin{code}
+tcGen :: TcSigmaType -- expected_ty
+ -> TcTyVarSet -- Extra tyvars that the universally
+ -- quantified tyvars of expected_ty
+ -- must not be unified
+ -> (TcRhoType -> TcM (result, LIE)) -- spec_ty
+ -> TcM (ExprCoFn, result, LIE)
+ -- 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
+ = tcInstType SigTv expected_ty `thenNF_Tc` \ (forall_tvs, theta, phi_ty) ->
+
+ -- Type-check the arg and unify with poly type
+ thing_inside phi_ty `thenTc` \ (result, lie) ->
+
+ -- Check that the "forall_tvs" havn't been constrained
+ -- The interesting bit here is that we must include the free variables
+ -- of the expected_ty. Here's an example:
+ -- runST (newVar True)
+ -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
+ -- for (newVar True), with s fresh. Then we unify with the runST's arg type
+ -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
+ -- So now s' isn't unconstrained because it's linked to a.
+ -- Conclusion: include the free vars of the expected_ty in the
+ -- list of "free vars" for the signature check.
+
+ newDicts SignatureOrigin theta `thenNF_Tc` \ dicts ->
+ tcSimplifyCheck sig_msg forall_tvs dicts lie `thenTc` \ (free_lie, inst_binds) ->
+ checkSigTyVarsWrt free_tvs forall_tvs `thenTc` \ zonked_tvs ->
+
+ 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 e = TyLam zonked_tvs (DictLam dict_ids (mkHsLet inst_binds e))
+ in
+ returnTc (mkCoercion co_fn, result, free_lie)
+ where
+ free_tvs = tyVarsOfType expected_ty `unionVarSet` extra_tvs
+ sig_msg = ptext SLIT("When generalising the type of an expression")
+\end{code}
+
+
+
+%************************************************************************
+%* *
+\subsection{Coercion functions}
+%* *
+%************************************************************************
+
+\begin{code}
+type Coercion a = Maybe (a -> a)
+ -- Nothing => identity fn
+
+type ExprCoFn = Coercion TypecheckedHsExpr
+type PatCoFn = Coercion TcPat
+
+(<.>) :: Coercion a -> Coercion a -> Coercion a -- Composition
+Nothing <.> Nothing = Nothing
+Nothing <.> Just f = Just f
+Just f <.> Nothing = Just f
+Just f1 <.> Just f2 = Just (f1 . f2)
+
+(<$>) :: Coercion a -> a -> a
+Just f <$> e = f e
+Nothing <$> e = e
+
+mkCoercion :: (a -> a) -> Coercion a
+mkCoercion f = Just f
+
+idCoercion :: Coercion a
+idCoercion = Nothing
+
+isIdCoercion :: Coercion a -> Bool
+isIdCoercion = isNothing
+\end{code}
+
+%************************************************************************
+%* *
\subsection[Unify-exported]{Exported unification functions}
%* *
%************************************************************************
\begin{code}
unifyTauTy :: TcTauType -> TcTauType -> TcM ()
unifyTauTy ty1 ty2 -- ty1 expected, ty2 inferred
- = tcAddErrCtxtM (unifyCtxt "type" ty1 ty2) $
+ = -- The unifier should only ever see tau-types
+ -- (no quantification whatsoever)
+ ASSERT2( isTauTy ty1, ppr ty1 )
+ ASSERT2( isTauTy ty2, ppr ty2 )
+ tcAddErrCtxtM (unifyCtxt "type" ty1 ty2) $
uTys ty1 ty1 ty2 ty2
\end{code}
-> TcM ()
-- Always expand synonyms (see notes at end)
- -- (this also throws away FTVs and usage annots)
-uTys ps_ty1 (NoteTy _ ty1) ps_ty2 ty2 = uTys ps_ty1 ty1 ps_ty2 ty2
-uTys ps_ty1 ty1 ps_ty2 (NoteTy _ ty2) = uTys ps_ty1 ty1 ps_ty2 ty2
+ -- (this also throws away FTVs)
+uTys ps_ty1 (NoteTy n1 ty1) ps_ty2 ty2 = uTys ps_ty1 ty1 ps_ty2 ty2
+uTys ps_ty1 ty1 ps_ty2 (NoteTy n2 ty2) = uTys ps_ty1 ty1 ps_ty2 ty2
-- Variables; go for uVar
uTys ps_ty1 (TyVarTy tyvar1) ps_ty2 ty2 = uVar False tyvar1 ps_ty2 ty2
-- "True" means args swapped
-- Predicates
-uTys _ (PredTy (IParam n1 t1)) _ (PredTy (IParam n2 t2))
+uTys _ (SourceTy (IParam n1 t1)) _ (SourceTy (IParam n2 t2))
| n1 == n2 = uTys t1 t1 t2 t2
-uTys _ (PredTy (Class c1 tys1)) _ (PredTy (Class c2 tys2))
+uTys _ (SourceTy (ClassP c1 tys1)) _ (SourceTy (ClassP c2 tys2))
| c1 == c2 = unifyTauTyLists tys1 tys2
+uTys _ (SourceTy (NType tc1 tys1)) _ (SourceTy (NType tc2 tys2))
+ | tc1 == tc2 = unifyTauTyLists tys1 tys2
-- Functions; just check the two parts
uTys _ (FunTy fun1 arg1) _ (FunTy fun2 arg2)
-- Type constructors must match
uTys ps_ty1 (TyConApp con1 tys1) ps_ty2 (TyConApp con2 tys2)
- | con1 == con2 && length tys1 == length tys2
+ | con1 == con2 && equalLength tys1 tys2
= unifyTauTyLists tys1 tys2
| con1 == openKindCon
-- 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
uTys ps_ty1 (AppTy s1 t1) ps_ty2 ty2
- = case splitAppTy_maybe ty2 of
+ = case tcSplitAppTy_maybe ty2 of
Just (s2,t2) -> uTys s1 s1 s2 s2 `thenTc_` uTys t1 t1 t2 t2
Nothing -> unifyMisMatch ps_ty1 ps_ty2
-- Now the same, but the other way round
-- Don't swap the types, because the error messages get worse
uTys ps_ty1 ty1 ps_ty2 (AppTy s2 t2)
- = case splitAppTy_maybe ty1 of
+ = case tcSplitAppTy_maybe ty1 of
Just (s1,t1) -> uTys s1 s1 s2 s2 `thenTc_` uTys t1 t1 t2 t2
Nothing -> unifyMisMatch ps_ty1 ps_ty2
uTys ps_ty1 ty1 ps_ty2 ty2 = unifyMisMatch ps_ty1 ps_ty2
\end{code}
+
Notes on synonyms
~~~~~~~~~~~~~~~~~
If you are tempted to make a short cut on synonyms, as in this
pseudocode...
\begin{verbatim}
-uTys (SynTy con1 args1 ty1) (SynTy con2 args2 ty2)
- = if (con1 == con2) then
- -- Good news! Same synonym constructors, so we can shortcut
- -- by unifying their arguments and ignoring their expansions.
- unifyTauTypeLists args1 args2
- else
- -- Never mind. Just expand them and try again
- uTys ty1 ty2
+-- NO uTys (SynTy con1 args1 ty1) (SynTy con2 args2 ty2)
+-- NO = if (con1 == con2) then
+-- NO -- Good news! Same synonym constructors, so we can shortcut
+-- NO -- by unifying their arguments and ignoring their expansions.
+-- NO unifyTauTypeLists args1 args2
+-- NO else
+-- NO -- Never mind. Just expand them and try again
+-- NO uTys ty1 ty2
\end{verbatim}
then THINK AGAIN. Here is the whole story, as detected and reported
-> TcM ()
uVar swapped tv1 ps_ty2 ty2
- = tcGetTyVar tv1 `thenNF_Tc` \ maybe_ty1 ->
+ = traceTc (text "uVar" <+> ppr swapped <+> ppr tv1 <+> (ppr ps_ty2 $$ ppr ty2)) `thenNF_Tc_`
+ getTcTyVar tv1 `thenNF_Tc` \ maybe_ty1 ->
case maybe_ty1 of
Just ty1 | swapped -> uTys ps_ty2 ty2 ty1 ty1 -- Swap back
| otherwise -> uTys ty1 ty1 ps_ty2 ty2 -- Same order
other -> uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2
- -- Expand synonyms; ignore FTVs; ignore usage annots
-uUnboundVar swapped tv1 maybe_ty1 ps_ty2 (NoteTy _ ty2)
+ -- Expand synonyms; ignore FTVs
+uUnboundVar swapped tv1 maybe_ty1 ps_ty2 (NoteTy n2 ty2)
= uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2
-- Distinct type variables
-- ASSERT maybe_ty1 /= Just
| otherwise
- = tcGetTyVar tv2 `thenNF_Tc` \ maybe_ty2 ->
+ = getTcTyVar tv2 `thenNF_Tc` \ maybe_ty2 ->
case maybe_ty2 of
Just ty2' -> uUnboundVar swapped tv1 maybe_ty1 ty2' ty2'
- Nothing | tv1_dominates_tv2
+ Nothing | update_tv2
-> WARN( not (k1 `hasMoreBoxityInfo` k2), (ppr tv1 <+> ppr k1) $$ (ppr tv2 <+> ppr k2) )
- tcPutTyVar tv2 (TyVarTy tv1) `thenNF_Tc_`
+ putTcTyVar tv2 (TyVarTy tv1) `thenNF_Tc_`
returnTc ()
| otherwise
-> WARN( not (k2 `hasMoreBoxityInfo` k1), (ppr tv2 <+> ppr k2) $$ (ppr tv1 <+> ppr k1) )
- (ASSERT( isNotUsgTy ps_ty2 )
- tcPutTyVar tv1 ps_ty2 `thenNF_Tc_`
- returnTc ())
+ putTcTyVar tv1 ps_ty2 `thenNF_Tc_`
+ returnTc ()
where
k1 = tyVarKind tv1
k2 = tyVarKind tv2
- tv1_dominates_tv2 = isSigTyVar tv1
+ update_tv2 = (k2 `eqKind` openTypeKind) || (not (k1 `eqKind` openTypeKind) && nicer_to_update_tv2)
+ -- Try to get rid of open type variables as soon as poss
+
+ nicer_to_update_tv2 = isUserTyVar tv1
-- Don't unify a signature type variable if poss
- || k2 == openTypeKind
- -- Try to get rid of open type variables as soon as poss
- || varName tv1 `hasBetterProv` varName tv2
+ || isSystemName (varName tv2)
-- Try to update sys-y type variables in preference to sig-y ones
-- Second one isn't a type variable
uUnboundVar swapped tv1 maybe_ty1 ps_ty2 non_var_ty2
- = checkKinds swapped tv1 non_var_ty2 `thenTc_`
- occur_check non_var_ty2 `thenTc_`
- ASSERT( isNotUsgTy ps_ty2 )
- checkTcM (not (isSigTyVar tv1))
+ = -- Check that tv1 isn't a type-signature type variable
+ checkTcM (not (isSkolemTyVar tv1))
(failWithTcM (unifyWithSigErr tv1 ps_ty2)) `thenTc_`
- warnTc (not (typeKind non_var_ty2 `hasMoreBoxityInfo` tyVarKind tv1))
- ((ppr tv1 <+> ppr (tyVarKind tv1)) $$
- (ppr non_var_ty2 <+> ppr (typeKind non_var_ty2))) `thenNF_Tc_`
-
- tcPutTyVar tv1 non_var_ty2 `thenNF_Tc_`
- -- This used to say "ps_ty2" instead of "non_var_ty2"
-
- -- But that led to an infinite loop in the type checker!
- -- Consider
- -- type A a = ()
- --
- -- f :: (A a -> a -> ()) -> ()
- -- f = \ _ -> ()
- --
- -- x :: ()
- -- x = f (\ x p -> p x)
- --
- -- Here, we try to match "t" with "A t", and succeed
- -- because the unifier looks through synonyms. The occurs
- -- check doesn't kick in because we are "really" binding "t" to "()",
- -- but we *actually* bind "t" to "A t" if we store ps_ty2.
- -- That leads the typechecker into an infinite loop later.
-
- returnTc ()
- where
- occur_check ty = mapTc occur_check_tv (varSetElems (tyVarsOfType ty)) `thenTc_`
- returnTc ()
+ -- Do the occurs check, and check that we are not
+ -- unifying a type variable with a polytype
+ -- Returns a zonked type ready for the update
+ checkValue tv1 ps_ty2 non_var_ty2 `thenTc` \ ty2 ->
- occur_check_tv tv2
- | tv1 == tv2 -- Same tyvar; fail
- = zonkTcType ps_ty2 `thenNF_Tc` \ zonked_ty2 ->
- failWithTcM (unifyOccurCheck tv1 zonked_ty2)
+ -- Check that the kinds match
+ checkKinds swapped tv1 ty2 `thenTc_`
- | otherwise -- A different tyvar
- = tcGetTyVar tv2 `thenNF_Tc` \ maybe_ty2 ->
- case maybe_ty2 of
- Just ty2' -> occur_check ty2'
- other -> returnTc ()
+ -- Perform the update
+ putTcTyVar tv1 ty2 `thenNF_Tc_`
+ returnTc ()
+\end{code}
+\begin{code}
checkKinds swapped tv1 ty2
-- We're about to unify a type variable tv1 with a non-tyvar-type ty2.
--- We need to check that we don't unify a boxed type variable with an
--- unboxed type: e.g. (id 3#) is illegal
- | tk1 == boxedTypeKind && tk2 == unboxedTypeKind
+-- ty2 has been zonked at this stage, which ensures that
+-- its kind has as much boxity information visible as possible.
+ | tk2 `hasMoreBoxityInfo` tk1 = returnTc ()
+
+ | 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
= tcAddErrCtxtM (unifyKindCtxt swapped tv1 ty2) $
unifyMisMatch k1 k2
- | otherwise
- = returnTc ()
+
where
(k1,k2) | swapped = (tk2,tk1)
| otherwise = (tk1,tk2)
tk2 = typeKind ty2
\end{code}
+\begin{code}
+checkValue tv1 ps_ty2 non_var_ty2
+-- Do the occurs check, and check that we are not
+-- unifying a type variable with a polytype
+-- Return the type to update the type variable with, or fail
+
+-- 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).
+--
+-- That's why we have this two-state occurs-check
+ = zonkTcType ps_ty2 `thenNF_Tc` \ ps_ty2' ->
+ case okToUnifyWith tv1 ps_ty2' of {
+ Nothing -> returnTc ps_ty2' ; -- Success
+ other ->
+
+ zonkTcType non_var_ty2 `thenNF_Tc` \ non_var_ty2' ->
+ case okToUnifyWith tv1 non_var_ty2' of
+ Nothing -> -- This branch rarely succeeds, except in strange cases
+ -- like that in the example above
+ returnTc non_var_ty2'
+
+ Just problem -> failWithTcM (unifyCheck problem tv1 ps_ty2')
+ }
+
+data Problem = OccurCheck | NotMonoType
+
+okToUnifyWith :: TcTyVar -> TcType -> Maybe Problem
+-- (okToUnifyWith tv ty) checks whether it's ok to unify
+-- tv :=: ty
+-- Nothing => ok
+-- Just p => not ok, problem p
+
+okToUnifyWith tv ty
+ = ok ty
+ where
+ ok (TyVarTy tv') | tv == tv' = Just OccurCheck
+ | otherwise = Nothing
+ ok (AppTy t1 t2) = ok t1 `and` ok t2
+ ok (FunTy t1 t2) = ok t1 `and` ok t2
+ ok (TyConApp _ ts) = oks ts
+ ok (ForAllTy _ _) = Just NotMonoType
+ ok (SourceTy st) = ok_st st
+ ok (NoteTy (FTVNote _) t) = ok t
+ ok (NoteTy (SynNote t1) t2) = ok t1 `and` ok t2
+ -- Type variables may be free in t1 but not t2
+ -- A forall may be in t2 but not t1
+
+ oks ts = foldr (and . ok) Nothing ts
+
+ ok_st (ClassP _ ts) = oks ts
+ ok_st (IParam _ t) = ok t
+ ok_st (NType _ ts) = oks ts
+
+ Nothing `and` m = m
+ Just p `and` m = Just p
+\end{code}
%************************************************************************
%* *
%* *
%************************************************************************
-@unifyFunTy@ is used to avoid the fruitless creation of type variables.
+@subFunTy@ and @unifyFunTy@ is used to avoid the fruitless
+creation of type variables.
+
+* subFunTy is used when we might be faced with a "hole" type variable,
+ in which case we should create two new holes.
+
+* unifyFunTy is used when we expect to encounter only "ordinary"
+ type variables, so we should create new ordinary type variables
\begin{code}
-unifyFunTy :: TcType -- Fail if ty isn't a function type
+subFunTy :: TcHoleType -- Fail if ty isn't a function type
+ -- If it's a hole, make two holes, feed them to...
+ -> (TcHoleType -> TcHoleType -> TcM a) -- the thing inside
+ -> TcM a -- and bind the function type to the hole
+
+subFunTy ty@(TyVarTy tyvar) thing_inside
+ | isHoleTyVar tyvar
+ = -- This is the interesting case
+ getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
+ case maybe_ty of {
+ Just ty' -> subFunTy ty' thing_inside ;
+ Nothing ->
+
+ newHoleTyVarTy `thenNF_Tc` \ arg_ty ->
+ newHoleTyVarTy `thenNF_Tc` \ res_ty ->
+
+ -- Do the business
+ thing_inside arg_ty res_ty `thenTc` \ answer ->
+
+ -- Extract the answers
+ readHoleResult arg_ty `thenNF_Tc` \ arg_ty' ->
+ readHoleResult res_ty `thenNF_Tc` \ res_ty' ->
+
+ -- Write the answer into the incoming hole
+ putTcTyVar tyvar (mkFunTy arg_ty' res_ty') `thenNF_Tc_`
+
+ -- And return the answer
+ returnTc answer }
+
+subFunTy ty thing_inside
+ = unifyFunTy ty `thenTc` \ (arg,res) ->
+ thing_inside arg res
+
+
+unifyFunTy :: TcRhoType -- Fail if ty isn't a function type
-> TcM (TcType, TcType) -- otherwise return arg and result types
unifyFunTy ty@(TyVarTy tyvar)
- = tcGetTyVar tyvar `thenNF_Tc` \ maybe_ty ->
+ = ASSERT( not (isHoleTyVar tyvar) )
+ getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
case maybe_ty of
Just ty' -> unifyFunTy ty'
- other -> unify_fun_ty_help ty
+ Nothing -> unify_fun_ty_help ty
unifyFunTy ty
- = case splitFunTy_maybe ty of
+ = case tcSplitFunTy_maybe ty of
Just arg_and_res -> returnTc arg_and_res
Nothing -> unify_fun_ty_help ty
-> TcM TcType -- list element type
unifyListTy ty@(TyVarTy tyvar)
- = tcGetTyVar tyvar `thenNF_Tc` \ maybe_ty ->
+ = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
case maybe_ty of
Just ty' -> unifyListTy ty'
- other -> unify_list_ty_help ty
+ other -> unify_list_ty_help ty
unifyListTy ty
- = case splitTyConApp_maybe ty of
+ = case tcSplitTyConApp_maybe ty of
Just (tycon, [arg_ty]) | tycon == listTyCon -> returnTc arg_ty
other -> unify_list_ty_help ty
unify_list_ty_help ty -- Revert to ordinary unification
- = newTyVarTy boxedTypeKind `thenNF_Tc` \ elt_ty ->
+ = newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
unifyTauTy ty (mkListTy elt_ty) `thenTc_`
returnTc elt_ty
+
+-- variant for parallel arrays
+--
+unifyPArrTy :: TcType -- expected list type
+ -> TcM TcType -- list element type
+
+unifyPArrTy ty@(TyVarTy tyvar)
+ = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
+ case maybe_ty of
+ Just ty' -> unifyPArrTy ty'
+ _ -> unify_parr_ty_help ty
+unifyPArrTy ty
+ = case tcSplitTyConApp_maybe ty of
+ Just (tycon, [arg_ty]) | tycon == parrTyCon -> returnTc arg_ty
+ _ -> unify_parr_ty_help ty
+
+unify_parr_ty_help ty -- Revert to ordinary unification
+ = newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
+ unifyTauTy ty (mkPArrTy elt_ty) `thenTc_`
+ returnTc elt_ty
\end{code}
\begin{code}
unifyTupleTy :: Boxity -> Arity -> TcType -> TcM [TcType]
unifyTupleTy boxity arity ty@(TyVarTy tyvar)
- = tcGetTyVar tyvar `thenNF_Tc` \ maybe_ty ->
+ = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
case maybe_ty of
Just ty' -> unifyTupleTy boxity arity ty'
other -> unify_tuple_ty_help boxity arity ty
unifyTupleTy boxity arity ty
- = case splitTyConApp_maybe ty of
+ = case tcSplitTyConApp_maybe ty of
Just (tycon, arg_tys)
| isTupleTyCon tycon
&& tyConArity tycon == arity
unifyTauTy ty (mkTupleTy boxity arity arg_tys) `thenTc_`
returnTc arg_tys
where
- kind | isBoxed boxity = boxedTypeKind
+ kind | isBoxed boxity = liftedTypeKind
| otherwise = openTypeKind
\end{code}
%************************************************************************
%* *
+\subsection{Kind unification}
+%* *
+%************************************************************************
+
+\begin{code}
+unifyKind :: TcKind -- Expected
+ -> TcKind -- Actual
+ -> TcM ()
+unifyKind k1 k2
+ = tcAddErrCtxtM (unifyCtxt "kind" k1 k2) $
+ uTys k1 k1 k2 k2
+
+unifyKinds :: [TcKind] -> [TcKind] -> TcM ()
+unifyKinds [] [] = returnTc ()
+unifyKinds (k1:ks1) (k2:ks2) = unifyKind k1 k2 `thenTc_`
+ unifyKinds ks1 ks2
+unifyKinds _ _ = panic "unifyKinds: length mis-match"
+\end{code}
+
+\begin{code}
+unifyOpenTypeKind :: TcKind -> TcM ()
+-- Ensures that the argument kind is of the form (Type bx)
+-- for some boxity bx
+
+unifyOpenTypeKind ty@(TyVarTy tyvar)
+ = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
+ case maybe_ty of
+ Just ty' -> unifyOpenTypeKind ty'
+ other -> unify_open_kind_help ty
+
+unifyOpenTypeKind ty
+ | isTypeKind ty = returnTc ()
+ | otherwise = unify_open_kind_help ty
+
+unify_open_kind_help ty -- Revert to ordinary unification
+ = newBoxityVar `thenNF_Tc` \ boxity ->
+ unifyKind ty (mkTyConApp typeCon [boxity])
+\end{code}
+
+
+%************************************************************************
+%* *
\subsection[Unify-context]{Errors and contexts}
%* *
%************************************************************************
where
(pp_expected, pp_actual) | swapped = (pp2, pp1)
| otherwise = (pp1, pp2)
- (env1, tv1') = tidyTyVar tidy_env tv1
+ (env1, tv1') = tidyOpenTyVar tidy_env tv1
(env2, ty2') = tidyOpenType env1 ty2
pp1 = ppr tv1'
pp2 = ppr ty2'
= (env2, hang (ptext SLIT("Cannot unify the type-signature variable") <+> quotes (ppr tidy_tyvar))
4 (ptext SLIT("with the type") <+> quotes (ppr tidy_ty)))
where
- (env1, tidy_tyvar) = tidyTyVar emptyTidyEnv tyvar
- (env2, tidy_ty) = tidyOpenType env1 ty
+ (env1, tidy_tyvar) = tidyOpenTyVar emptyTidyEnv tyvar
+ (env2, tidy_ty) = tidyOpenType env1 ty
-unifyOccurCheck tyvar ty
- = (env2, hang (ptext SLIT("Occurs check: cannot construct the infinite type:"))
+unifyCheck problem tyvar ty
+ = (env2, hang msg
4 (sep [ppr tidy_tyvar, char '=', ppr tidy_ty]))
where
- (env1, tidy_tyvar) = tidyTyVar emptyTidyEnv tyvar
- (env2, tidy_ty) = tidyOpenType env1 ty
+ (env1, tidy_tyvar) = tidyOpenTyVar emptyTidyEnv tyvar
+ (env2, tidy_ty) = tidyOpenType env1 ty
+
+ msg = case problem of
+ OccurCheck -> ptext SLIT("Occurs check: cannot construct the infinite type:")
+ NotMonoType -> ptext SLIT("Cannot unify a type variable with a type scheme:")
\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Checking signature type variables}
+%* *
+%************************************************************************
+
+@checkSigTyVars@ is used after the type in a type signature has been unified with
+the actual type found. It then checks that the type variables of the type signature
+are
+ (a) Still all type variables
+ eg matching signature [a] against inferred type [(p,q)]
+ [then a will be unified to a non-type variable]
+
+ (b) Still all distinct
+ eg matching signature [(a,b)] against inferred type [(p,p)]
+ [then a and b will be unified together]
+
+ (c) Not mentioned in the environment
+ eg the signature for f in this:
+
+ g x = ... where
+ f :: a->[a]
+ f y = [x,y]
+
+ Here, f is forced to be monorphic by the free occurence of x.
+
+ (d) Not (unified with another type variable that is) in scope.
+ eg f x :: (r->r) = (\y->y) :: forall a. a->r
+ when checking the expression type signature, we find that
+ even though there is nothing in scope whose type mentions r,
+ nevertheless the type signature for the expression isn't right.
+
+ Another example is in a class or instance declaration:
+ class C a where
+ op :: forall b. a -> b
+ op x = x
+ Here, b gets unified with a
+
+Before doing this, the substitution is applied to the signature type variable.
+
+We used to have the notion of a "DontBind" type variable, which would
+only be bound to itself or nothing. Then points (a) and (b) were
+self-checking. But it gave rise to bogus consequential error messages.
+For example:
+
+ f = (*) -- Monomorphic
+
+ g :: Num a => a -> a
+ g x = f x x
+
+Here, we get a complaint when checking the type signature for g,
+that g isn't polymorphic enough; but then we get another one when
+dealing with the (Num x) context arising from f's definition;
+we try to unify x with Int (to default it), but find that x has already
+been unified with the DontBind variable "a" from g's signature.
+This is really a problem with side-effecting unification; we'd like to
+undo g's effects when its type signature fails, but unification is done
+by side effect, so we can't (easily).
+
+So we revert to ordinary type variables for signatures, and try to
+give a helpful message in checkSigTyVars.
+
+\begin{code}
+checkSigTyVars :: [TcTyVar] -> TcM [TcTyVar]
+checkSigTyVars sig_tvs = check_sig_tyvars emptyVarSet sig_tvs
+
+checkSigTyVarsWrt :: TcTyVarSet -> [TcTyVar] -> TcM [TcTyVar]
+checkSigTyVarsWrt extra_tvs sig_tvs
+ = zonkTcTyVarsAndFV (varSetElems extra_tvs) `thenNF_Tc` \ extra_tvs' ->
+ check_sig_tyvars extra_tvs' sig_tvs
+
+check_sig_tyvars
+ :: TcTyVarSet -- Global type variables. The universally quantified
+ -- tyvars should not mention any of these
+ -- Guaranteed already zonked.
+ -> [TcTyVar] -- Universally-quantified type variables in the signature
+ -- Not guaranteed zonked.
+ -> TcM [TcTyVar] -- Zonked signature type variables
+
+check_sig_tyvars extra_tvs []
+ = returnTc []
+check_sig_tyvars extra_tvs sig_tvs
+ = zonkTcTyVars sig_tvs `thenNF_Tc` \ sig_tys ->
+ tcGetGlobalTyVars `thenNF_Tc` \ gbl_tvs ->
+ let
+ env_tvs = gbl_tvs `unionVarSet` extra_tvs
+ in
+ checkTcM (allDistinctTyVars sig_tys env_tvs)
+ (complain sig_tys env_tvs) `thenTc_`
+
+ returnTc (map (tcGetTyVar "checkSigTyVars") sig_tys)
+
+ where
+ complain sig_tys globals
+ = -- "check" checks each sig tyvar in turn
+ foldlNF_Tc check
+ (env2, emptyVarEnv, [])
+ (tidy_tvs `zip` tidy_tys) `thenNF_Tc` \ (env3, _, msgs) ->
+
+ failWithTcM (env3, main_msg $$ nest 4 (vcat msgs))
+ where
+ (env1, tidy_tvs) = tidyOpenTyVars emptyTidyEnv sig_tvs
+ (env2, tidy_tys) = tidyOpenTypes env1 sig_tys
+
+ main_msg = ptext SLIT("Inferred type is less polymorphic than expected")
+
+ check (tidy_env, acc, msgs) (sig_tyvar,ty)
+ -- sig_tyvar is from the signature;
+ -- ty is what you get if you zonk sig_tyvar and then tidy it
+ --
+ -- acc maps a zonked type variable back to a signature type variable
+ = case tcGetTyVar_maybe ty of {
+ Nothing -> -- Error (a)!
+ returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar (quotes (ppr ty)) : msgs) ;
+
+ Just tv ->
+
+ case lookupVarEnv acc tv of {
+ Just sig_tyvar' -> -- Error (b)!
+ returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar thing : msgs)
+ where
+ thing = ptext SLIT("another quantified type variable") <+> quotes (ppr sig_tyvar')
+
+ ; Nothing ->
+
+ if tv `elemVarSet` globals -- Error (c) or (d)! Type variable escapes
+ -- The least comprehensible, so put it last
+ -- Game plan:
+ -- get the local TcIds and TyVars from the environment,
+ -- and pass them to find_globals (they might have tv free)
+ then tcGetEnv `thenNF_Tc` \ ve ->
+ find_globals tv tidy_env (tcLEnvElts ve) `thenNF_Tc` \ (tidy_env1, globs) ->
+ returnNF_Tc (tidy_env1, acc, escape_msg sig_tyvar tv globs : msgs)
+
+ else -- All OK
+ returnNF_Tc (tidy_env, extendVarEnv acc tv sig_tyvar, msgs)
+ }}
+\end{code}
+
+
+\begin{code}
+-----------------------
+-- find_globals looks at the value environment and finds values
+-- whose types mention the offending type variable. It has to be
+-- careful to zonk the Id's type first, so it has to be in the monad.
+-- We must be careful to pass it a zonked type variable, too.
+
+find_globals :: Var
+ -> TidyEnv
+ -> [TcTyThing]
+ -> NF_TcM (TidyEnv, [SDoc])
+
+find_globals tv tidy_env things
+ = go tidy_env [] things
+ where
+ go tidy_env acc [] = returnNF_Tc (tidy_env, acc)
+ go tidy_env acc (thing : things)
+ = find_thing ignore_it tidy_env thing `thenNF_Tc` \ (tidy_env1, maybe_doc) ->
+ case maybe_doc of
+ Just d -> go tidy_env1 (d:acc) things
+ Nothing -> go tidy_env1 acc things
+
+ ignore_it ty = not (tv `elemVarSet` tyVarsOfType ty)
+
+-----------------------
+find_thing ignore_it tidy_env (ATcId id)
+ = zonkTcType (idType id) `thenNF_Tc` \ id_ty ->
+ if ignore_it id_ty then
+ returnNF_Tc (tidy_env, Nothing)
+ else let
+ (tidy_env', tidy_ty) = tidyOpenType tidy_env id_ty
+ msg = sep [ppr id <+> dcolon <+> ppr tidy_ty,
+ nest 2 (parens (ptext SLIT("bound at") <+>
+ ppr (getSrcLoc id)))]
+ in
+ returnNF_Tc (tidy_env', Just msg)
+
+find_thing ignore_it tidy_env (ATyVar tv)
+ = zonkTcTyVar tv `thenNF_Tc` \ tv_ty ->
+ if ignore_it tv_ty then
+ returnNF_Tc (tidy_env, Nothing)
+ else let
+ (tidy_env1, tv1) = tidyOpenTyVar tidy_env tv
+ (tidy_env2, tidy_ty) = tidyOpenType tidy_env1 tv_ty
+ msg = sep [ppr tv1 <+> eq_stuff, nest 2 bound_at]
+
+ eq_stuff | Just tv' <- Type.getTyVar_maybe tv_ty, tv == tv' = empty
+ | otherwise = equals <+> ppr tv_ty
+ -- It's ok to use Type.getTyVar_maybe because ty is zonked by now
+
+ bound_at = tyVarBindingInfo tv
+ in
+ returnNF_Tc (tidy_env2, Just msg)
+
+-----------------------
+escape_msg sig_tv tv globs
+ = mk_msg sig_tv <+> ptext SLIT("escapes") $$
+ if not (null globs) then
+ vcat [pp_it <+> ptext SLIT("is mentioned in the environment:"),
+ nest 2 (vcat globs)]
+ else
+ empty -- Sigh. It's really hard to give a good error message
+ -- all the time. One bad case is an existential pattern match.
+ -- We rely on the "When..." context to help.
+ where
+ pp_it | sig_tv /= tv = ptext SLIT("It unifies with") <+> quotes (ppr tv) <> comma <+> ptext SLIT("which")
+ | otherwise = ptext SLIT("It")
+
+
+unify_msg tv thing = mk_msg tv <+> ptext SLIT("is unified with") <+> thing
+mk_msg tv = ptext SLIT("Quantified type variable") <+> quotes (ppr tv)
+\end{code}
+
+These two context are used with checkSigTyVars
+
+\begin{code}
+sigCtxt :: Id -> [TcTyVar] -> TcThetaType -> TcTauType
+ -> TidyEnv -> NF_TcM (TidyEnv, Message)
+sigCtxt id sig_tvs sig_theta sig_tau tidy_env
+ = zonkTcType sig_tau `thenNF_Tc` \ actual_tau ->
+ let
+ (env1, tidy_sig_tvs) = tidyOpenTyVars tidy_env sig_tvs
+ (env2, tidy_sig_rho) = tidyOpenType env1 (mkPhiTy sig_theta sig_tau)
+ (env3, tidy_actual_tau) = tidyOpenType env2 actual_tau
+ sub_msg = vcat [ptext SLIT("Signature type: ") <+> pprType (mkForAllTys tidy_sig_tvs tidy_sig_rho),
+ ptext SLIT("Type to generalise:") <+> pprType tidy_actual_tau
+ ]
+ msg = vcat [ptext SLIT("When trying to generalise the type inferred for") <+> quotes (ppr id),
+ nest 4 sub_msg]
+ in
+ returnNF_Tc (env3, msg)
+\end{code}
projects / ghc-hetmet.git / blobdiff