import Inst ( InstOrigin(..),
LIE, mkLIE, emptyLIE, unitLIE, plusLIE, plusLIEs,
newOverloadedLit, newMethod, newIPDict,
- newDicts,
- instToId, tcInstId
+ newDicts, newMethodWithGivenTy,
+ instToId, tcInstCall
)
import TcBinds ( tcBindsAndThen )
import TcEnv ( tcLookupClass, tcLookupGlobalId, tcLookupGlobal_maybe,
import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
import TcPat ( badFieldCon )
import TcSimplify ( tcSimplifyIPs )
-import TcMType ( tcInstTyVars, newTyVarTy, newTyVarTys, zonkTcType )
+import TcMType ( tcInstTyVars, tcInstType, newHoleTyVarTy,
+ newTyVarTy, newTyVarTys, zonkTcType )
import TcType ( TcType, TcSigmaType, TcPhiType,
- tcSplitFunTys, tcSplitTyConApp,
+ tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
isSigmaTy, mkFunTy, mkAppTy, mkTyConTy,
mkTyConApp, mkClassPred, tcFunArgTy,
- tyVarsOfTypes,
+ tyVarsOfTypes, isLinearPred,
liftedTypeKind, openTypeKind, mkArrowKind,
tcSplitSigmaTy, tcTyConAppTyCon,
tidyOpenType
= tcHsSigType ExprSigCtxt poly_ty `thenTc` \ sig_tc_ty ->
tcAddErrCtxt (exprSigCtxt in_expr) $
tcExpr expr sig_tc_ty `thenTc` \ (expr', lie1) ->
- tcSub res_ty sig_tc_ty `thenTc` \ (co_fn, lie2) ->
- returnTc (co_fn <$> expr', lie1 `plusLIE` lie2)
+
+ -- Must instantiate the outer for-alls of sig_tc_ty
+ -- else we risk instantiating a ? res_ty to a forall-type
+ -- which breaks the invariant that tcMonoExpr only returns phi-types
+ tcInstCall SignatureOrigin sig_tc_ty `thenNF_Tc` \ (inst_fn, lie2, inst_sig_ty) ->
+ tcSub res_ty inst_sig_ty `thenTc` \ (co_fn, lie3) ->
+
+ returnTc (co_fn <$> inst_fn expr', lie1 `plusLIE` lie2 `plusLIE` lie3)
\end{code}
%* *
%************************************************************************
+tcId instantiates an occurrence of an Id.
+The instantiate_it loop runs round instantiating the Id.
+It has to be a loop because we are now prepared to entertain
+types like
+ f:: forall a. Eq a => forall b. Baz b => tau
+We want to instantiate this to
+ f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
+
+The -fno-method-sharing flag controls what happens so far as the LIE
+is concerned. The default case is that for an overloaded function we
+generate a "method" Id, and add the Method Inst to the LIE. So you get
+something like
+ f :: Num a => a -> a
+ f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
+If you specify -fno-method-sharing, the dictionary application
+isn't shared, so we get
+ f :: Num a => a -> a
+ f = /\a (d:Num a) (x:a) -> (+) a d x x
+This gets a bit less sharing, but
+ a) it's better for RULEs involving overloaded functions
+ b) perhaps fewer separated lambdas
+
\begin{code}
tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
tcId name -- Look up the Id and instantiate its type
= tcLookupId name `thenNF_Tc` \ id ->
- tcInstId id
+ loop (OccurrenceOf id) (HsVar id) emptyLIE (idType id)
+ where
+ loop orig (HsVar fun_id) lie fun_ty
+ | want_method_inst fun_ty
+ = tcInstType fun_ty `thenNF_Tc` \ (tyvars, theta, tau) ->
+ newMethodWithGivenTy orig fun_id
+ (mkTyVarTys tyvars) theta tau `thenNF_Tc` \ meth ->
+ loop orig (HsVar (instToId meth))
+ (unitLIE meth `plusLIE` lie) tau
+
+ loop orig fun lie fun_ty
+ | isSigmaTy fun_ty
+ = tcInstCall orig fun_ty `thenNF_Tc` \ (inst_fn, inst_lie, tau) ->
+ loop orig (inst_fn fun) (inst_lie `plusLIE` lie) tau
+
+ | otherwise
+ = returnNF_Tc (fun, lie, fun_ty)
+
+ want_method_inst fun_ty
+ | opt_NoMethodSharing = False
+ | otherwise = case tcSplitSigmaTy fun_ty of
+ (_,[],_) -> False -- Not overloaded
+ (_,theta,_) -> not (any isLinearPred theta)
+ -- This is a slight hack.
+ -- If f :: (%x :: T) => Int -> Int
+ -- Then if we have two separate calls, (f 3, f 4), we cannot
+ -- make a method constraint that then gets shared, thus:
+ -- let m = f %x in (m 3, m 4)
+ -- because that loses the linearity of the constraint.
+ -- The simplest thing to do is never to construct a method constraint
+ -- in the first place that has a linear implicit parameter in it.
\end{code}
Typecheck expression which in most cases will be an Id.
+The expression can return a higher-ranked type, such as
+ (forall a. a->a) -> Int
+so we must create a HoleTyVarTy to pass in as the expected tyvar.
\begin{code}
tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
tcExpr_id (HsVar name) = tcId name
-tcExpr_id expr = newTyVarTy openTypeKind `thenNF_Tc` \ id_ty ->
+tcExpr_id expr = newHoleTyVarTy `thenNF_Tc` \ id_ty ->
tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
returnTc (expr', lie_id, id_ty)
\end{code}
projects / ghc-hetmet.git / blobdiff