import TypeRep ( Type(..) )
import TyCon
import HsSyn
-import Id
import VarEnv
import VarSet
import Var
import Bag
import Outputable
import SrcLoc ( Located(..) )
+import Util ( debugIsOn )
import Maybes
+import MonadUtils
import FastString
-- standard
| not (isOpenSynTyCon tycon) -- unfold *only* _synonym_ family instances
= return Nothing
| otherwise
- = do { -- we only use the indexing arguments for matching,
- -- not the additional ones
- ; maybeFamInst <- tcLookupFamInst tycon idxTys
+ = do { -- The TyCon might be over-saturated, but that's ok for tcLookupFamInst
+ ; maybeFamInst <- tcLookupFamInst tycon tys
; case maybeFamInst of
Nothing -> return Nothing
- Just (rep_tc, rep_tys) -> return $ Just (mkTyConApp rep_tc tys',
- mkTyConApp coe_tc tys')
+ Just (rep_tc, rep_tys) -> return $ Just (mkTyConApp rep_tc rep_tys,
+ mkTyConApp coe_tc rep_tys)
where
- tys' = rep_tys ++ restTys
coe_tc = expectJust "TcTyFuns.tcUnfoldSynFamInst"
(tyConFamilyCoercion_maybe rep_tc)
}
- where
- n = tyConArity tycon
- (idxTys, restTys) = splitAt n tys
tcUnfoldSynFamInst _other = return Nothing
\end{code}
We maintain normalised equalities together with the skolems introduced as
intermediates during flattening of equalities as well as
-!!!TODO: We probably now can do without the skolem set. It's not used during
-finalisation in the current code.
-
\begin{code}
-- |Configuration of normalised equalities used during solving.
--
, binds = emptyBag
, skolems = emptyVarSet
}
+
+instance Outputable EqConfig where
+ ppr (EqConfig {eqs = eqs, locals = locals, wanteds = wanteds, binds = binds})
+ = vcat [ppr eqs, ppr locals, ppr wanteds, ppr binds]
\end{code}
The set of operations on an equality configuration. We obtain the initialise
--
normaliseEqs :: [Inst] -> TcM EqConfig
normaliseEqs eqs
- = do { ASSERTM2( allM isValidWantedEqInst eqs, ppr eqs )
- ; traceTc $ ptext (sLit "normaliseEqs")
+ = do { if debugIsOn then do { all_unsolved <- allM wantedEqInstIsUnsolved eqs
+ ; let msg = ptext (sLit "(This warning is harmless; for Simon & Manuel)")
+ ; WARN( not all_unsolved, msg $$ ppr eqs ) return () }
+ else return ()
+ -- This is just a warning (not an error) because a current
+ -- harmless bug means that we sometimes solve the same
+ -- equality more than once It'll go away with the new
+ -- solver. See Trac #2999 for example
+
+ ; traceTc $ ptext (sLit "Entering normaliseEqs")
; (eqss, skolemss) <- mapAndUnzipM normEqInst eqs
; return $ emptyEqConfig { eqs = concat eqss
--
normaliseDicts :: Bool -> [Inst] -> TcM EqConfig
normaliseDicts isWanted insts
- = do { traceTc $ ptext (sLit "normaliseDicts") <+>
- ptext (if isWanted then sLit "[Wanted]" else sLit "[Local]")
+ = do { traceTc $ hang (ptext (sLit "Entering normaliseDicts") <+>
+ ptext (if isWanted then sLit "[Wanted] for"
+ else sLit "[Local] for"))
+ 4 (ppr insts)
; (insts', eqss, bindss, skolemss) <- mapAndUnzip4M (normDict isWanted)
insts
+
+ ; traceTc $ hang (ptext (sLit "normaliseDicts returns"))
+ 4 (ppr insts' $$ ppr eqss)
; return $ emptyEqConfig { eqs = concat eqss
, locals = if isWanted then [] else insts'
, wanteds = if isWanted then insts' else []
--
propagateEqs :: EqConfig -> TcM EqConfig
propagateEqs eqCfg@(EqConfig {eqs = todoEqs})
- = do { traceTc $ ptext (sLit "propagateEqs")
+ = do { traceTc $ hang (ptext (sLit "Entering propagateEqs:"))
+ 4 (ppr eqCfg)
+
; propagate todoEqs (eqCfg {eqs = []})
}
-- set of instances are the locals (without equalities) and the second set are
-- all residual wanteds, including equalities.
--
--- Remove all identity dictinary bindings (i.e., those whose source and target
--- dictionary are the same). This is important for termination, as
--- TcSimplify.reduceContext takes the presence of dictionary bindings as an
--- indicator that there was some improvement.
---
finaliseEqsAndDicts :: EqConfig
-> TcM ([Inst], [Inst], TcDictBinds, Bool)
finaliseEqsAndDicts (EqConfig { eqs = eqs
, locals = locals
, wanteds = wanteds
, binds = binds
+ , skolems = skolems
})
= do { traceTc $ ptext (sLit "finaliseEqsAndDicts")
; (eqs', subst_binds, locals', wanteds') <- substitute eqs locals wanteds
- ; (eqs'', improved) <- instantiateAndExtract eqs'
- ; final_binds <- filterM nonTrivialDictBind $
- bagToList (subst_binds `unionBags` binds)
-
- ; ASSERTM2( allM isValidWantedEqInst eqs'', ppr eqs'' )
- ; return (locals', eqs'' ++ wanteds', listToBag final_binds, improved)
+ ; (eqs'', improved) <- instantiateAndExtract eqs' (null locals) skolems
+ ; let final_binds = subst_binds `unionBags` binds
+
+ -- Assert that all cotvs of wanted equalities are still unfilled, and
+ -- zonk all final insts, to make any improvement visible
+ ; ASSERTM2( allM wantedEqInstIsUnsolved eqs'', ppr eqs'' )
+ ; zonked_locals <- zonkInsts locals'
+ ; zonked_wanteds <- zonkInsts (eqs'' ++ wanteds')
+ ; return (zonked_locals, zonked_wanteds, final_binds, improved)
}
- where
- nonTrivialDictBind (L _ (VarBind { var_id = ide1
- , var_rhs = L _ (HsWrap _ (HsVar ide2))}))
- = do { ty1 <- zonkTcType (idType ide1)
- ; ty2 <- zonkTcType (idType ide2)
- ; return $ not (ty1 `tcEqType` ty2)
- }
- nonTrivialDictBind _ = return True
\end{code}
A normal equality is a properly oriented equality with associated coercion
that contains at most one family equality (in its left-hand side) is oriented
-such that it may be used as a reqrite rule. It has one of the following two
+such that it may be used as a rewrite rule. It has one of the following two
forms:
(1) co :: F t1..tn ~ t (family equalities)
The types t, t1, ..., tn may not contain any occurrences of synonym
families. Moreover, in Forms (2) & (3), the left-hand side may not occur in
-the right-hand side, and the relation x > y is an arbitrary, but total order
-on type variables
-
-!!!TODO: We may need to keep track of swapping for error messages (and to
-re-orient on finilisation).
+the right-hand side, and the relation x > y is an (nearly) arbitrary, but
+total order on type variables. The only restriction that we impose on that
+order is that for x > y, we are happy to instantiate x with y taking into
+account kinds, signature skolems etc (cf, TcUnify.uUnfilledVars).
\begin{code}
data RewriteInst
where
swapped = rwi_swapped rewrite
(left, right) = if not swapped then (ty1, ty2) else (ty2, ty1)
+
+instance Outputable RewriteInst where
+ ppr (RewriteFam {rwi_fam = fam, rwi_args = args, rwi_right = rhs, rwi_co =co})
+ = hsep [ pprEqInstCo co <+> text "::"
+ , ppr (mkTyConApp fam args)
+ , text "~>"
+ , ppr rhs
+ ]
+ ppr (RewriteVar {rwi_var = tv, rwi_right = rhs, rwi_co =co})
+ = hsep [ pprEqInstCo co <+> text "::"
+ , ppr tv
+ , text "~>"
+ , ppr rhs
+ ]
+
+pprEqInstCo :: EqInstCo -> SDoc
+pprEqInstCo (Left cotv) = ptext (sLit "Wanted") <+> ppr cotv
+pprEqInstCo (Right co) = ptext (sLit "Local") <+> ppr co
\end{code}
The following functions turn an arbitrary equality into a set of normal
-- Normalise one equality.
normEqInst inst
= ASSERT( isEqInst inst )
- go ty1 ty2 (eqInstCoercion inst)
+ do { traceTc $ ptext (sLit "normEqInst of ") <+>
+ pprEqInstCo co <+> text "::" <+>
+ ppr ty1 <+> text "~" <+> ppr ty2
+ ; res <- go ty1 ty2 co
+ ; traceTc $ ptext (sLit "normEqInst returns") <+> ppr res
+ ; return res
+ }
where
(ty1, ty2) = eqInstTys inst
+ co = eqInstCoercion inst
-- look through synonyms
go ty1 ty2 co | Just ty1' <- tcView ty1 = go ty1' ty2 co
go ty1 ty2 co | Just ty2' <- tcView ty2 = go ty1 ty2' co
-- left-to-right rule with type family head
- go (TyConApp con args) ty2 co
- | isOpenSynTyCon con
+ go ty1@(TyConApp con args) ty2 co
+ | isOpenSynTyConApp ty1 -- only if not oversaturated
= mkRewriteFam False con args ty2 co
-- right-to-left rule with type family head
go ty1 ty2@(TyConApp con args) co
- | isOpenSynTyCon con
+ | isOpenSynTyConApp ty2 -- only if not oversaturated
= do { co' <- mkSymEqInstCo co (ty2, ty1)
; mkRewriteFam True con args ty1 co'
}
= do { (ty1', co1, ty1_eqs, ty1_skolems) <- flattenType inst ty1
; (ty2', co2, ty2_eqs, ty2_skolems) <- flattenType inst ty2
; let ty12_eqs = ty1_eqs ++ ty2_eqs
- rewriteCo = co1 `mkTransCoercion` mkSymCoercion co2
+ sym_co2 = mkSymCoercion co2
eqTys = (ty1', ty2')
- ; (co', ty12_eqs') <- adjustCoercions co rewriteCo eqTys ty12_eqs
+ ; (co', ty12_eqs') <- adjustCoercions co co1 sym_co2 eqTys ty12_eqs
; eqs <- checkOrientation ty1' ty2' co' inst
; if isLoopyEquality eqs ty12_eqs'
then do { if isWantedCo (tci_co inst)
= do { (args', cargs, args_eqss, args_skolemss)
<- mapAndUnzip4M (flattenType inst) args
; (ty2', co2, ty2_eqs, ty2_skolems) <- flattenType inst ty2
- ; let rewriteCo = mkTyConApp con cargs `mkTransCoercion`
- mkSymCoercion co2
+ ; let co1 = mkTyConApp con cargs
+ sym_co2 = mkSymCoercion co2
all_eqs = concat args_eqss ++ ty2_eqs
eqTys = (mkTyConApp con args', ty2')
- ; (co', all_eqs') <- adjustCoercions co rewriteCo eqTys all_eqs
+ ; (co', all_eqs') <- adjustCoercions co co1 sym_co2 eqTys all_eqs
; let thisRewriteFam = RewriteFam
{ rwi_fam = con
, rwi_args = args'
; eqs' <- if isWanted then return eqs else mapM wantedToLocal eqs
; return (inst', eqs', bind, unionVarSets args_skolemss)
}}
-normDict isWanted inst
+normDict _isWanted inst
= return (inst, [], emptyBag, emptyVarSet)
-- !!!TODO: Still need to normalise IP constraints.
; return []
}
- -- two tvs, left greater => unchanged
+ -- two tvs (distinct tvs, due to previous equation)
go ty1@(TyVarTy tv1) ty2@(TyVarTy tv2)
- | tv1 > tv2
- = mkRewriteVar False tv1 ty2 co
-
- -- two tvs, right greater => swap
- | otherwise
- = do { co' <- mkSymEqInstCo co (ty2, ty1)
- ; mkRewriteVar True tv2 ty1 co'
+ = do { isBigger <- tv1 `tvIsBigger` tv2
+ ; if isBigger -- left greater
+ then mkRewriteVar False tv1 ty2 co -- => unchanged
+ else do { co' <- mkSymEqInstCo co (ty2, ty1) -- right greater
+ ; mkRewriteVar True tv2 ty1 co' -- => swap
+ }
}
-- only lhs is a tv => unchanged
; mkRewriteVar True tv2 ty1 co'
}
+ -- data type constructor application => decompose
+ -- NB: Special cased for efficiency - could be handled as type application
+ go (TyConApp con1 args1) (TyConApp con2 args2)
+ | con1 == con2
+ && not (isOpenSynTyCon con1) -- don't match family synonym apps
+ = do { co_args <- mkTyConEqInstCo co con1 (zip args1 args2)
+ ; eqss <- zipWith3M (\ty1 ty2 co -> checkOrientation ty1 ty2 co inst)
+ args1 args2 co_args
+ ; return $ concat eqss
+ }
+
+ -- function type => decompose
+ -- NB: Special cased for efficiency - could be handled as type application
+ go (FunTy ty1_l ty1_r) (FunTy ty2_l ty2_r)
+ = do { (co_l, co_r) <- mkFunEqInstCo co (ty1_l, ty2_l) (ty1_r, ty2_r)
+ ; eqs_l <- checkOrientation ty1_l ty2_l co_l inst
+ ; eqs_r <- checkOrientation ty1_r ty2_r co_r inst
+ ; return $ eqs_l ++ eqs_r
+ }
+
-- type applications => decompose
go ty1 ty2
| Just (ty1_l, ty1_r) <- repSplitAppTy_maybe ty1 -- won't split fam apps
; eqs_r <- checkOrientation ty1_r ty2_r co_r inst
; return $ eqs_l ++ eqs_r
}
--- !!!TODO: would be more efficient to handle the FunApp and the data
--- constructor application explicitly.
-- inconsistency => type error
go ty1 ty2
, rwi_swapped = swapped
}]
+ -- if tv1 `tvIsBigger` tv2, we make a rewrite rule tv1 ~> tv2
+ tvIsBigger :: TcTyVar -> TcTyVar -> TcM Bool
+ tvIsBigger tv1 tv2
+ = isBigger tv1 (tcTyVarDetails tv1) tv2 (tcTyVarDetails tv2)
+ where
+ isBigger tv1 (SkolemTv _) tv2 (SkolemTv _)
+ = return $ tv1 > tv2
+ isBigger _ (MetaTv _ _) _ (SkolemTv _)
+ = return True
+ isBigger _ (SkolemTv _) _ (MetaTv _ _)
+ = return False
+ isBigger tv1 (MetaTv info1 _) tv2 (MetaTv info2 _)
+ -- meta variable meets meta variable
+ -- => be clever about which of the two to update
+ -- (from TcUnify.uUnfilledVars minus boxy stuff)
+ = case (info1, info2) of
+ -- Avoid SigTvs if poss
+ (SigTv _, SigTv _) -> return $ tv1 > tv2
+ (SigTv _, _ ) | k1_sub_k2 -> return False
+ (_, SigTv _) | k2_sub_k1 -> return True
+
+ (_, _)
+ | k1_sub_k2 &&
+ k2_sub_k1
+ -> case (nicer_to_update tv1, nicer_to_update tv2) of
+ (True, False) -> return True
+ (False, True) -> return False
+ _ -> return $ tv1 > tv2
+ | k1_sub_k2 -> return False
+ | k2_sub_k1 -> return True
+ | otherwise -> kind_err >> return True
+ -- Update the variable with least kind info
+ -- See notes on type inference in Kind.lhs
+ -- The "nicer to" part only applies if the two kinds are the same,
+ -- so we can choose which to do.
+ where
+ kind_err = addErrCtxtM (unifyKindCtxt False tv1 (mkTyVarTy tv2)) $
+ unifyKindMisMatch k1 k2
+
+ k1 = tyVarKind tv1
+ k2 = tyVarKind tv2
+ k1_sub_k2 = k1 `isSubKind` k2
+ k2_sub_k1 = k2 `isSubKind` k1
+
+ nicer_to_update tv = isSystemName (Var.varName tv)
+ -- Try to update sys-y type variables in preference to ones
+ -- gotten (say) by instantiating a polymorphic function with
+ -- a user-written type sig
+
flattenType :: Inst -- context to get location & name
-> Type -- the type to flatten
-> TcM (Type, -- the flattened type
= go ty
where
-- look through synonyms
- go ty | Just ty' <- tcView ty = go ty'
+ go ty | Just ty' <- tcView ty
+ = do { (ty_flat, co, eqs, skolems) <- go ty'
+ ; if null eqs
+ then -- unchanged, keep the old type with folded synonyms
+ return (ty, ty, [], emptyVarSet)
+ else
+ return (ty_flat, co, eqs, skolems)
+ }
-- type variable => nothing to do
go ty@(TyVarTy _)
= return (ty, ty, [] , emptyVarSet)
- -- type family application
+ -- type family application & family arity matches number of args
-- => flatten to "gamma :: F t1'..tn' ~ alpha" (alpha & gamma fresh)
go ty@(TyConApp con args)
- | isOpenSynTyCon con
+ | isOpenSynTyConApp ty -- only if not oversaturated
= do { (args', cargs, args_eqss, args_skolemss) <- mapAndUnzip4M go args
; alpha <- newFlexiTyVar (typeKind ty)
; let alphaTy = mkTyVarTy alpha
-- data constructor application => flatten subtypes
-- NB: Special cased for efficiency - could be handled as type application
- go (TyConApp con args)
+ go ty@(TyConApp con args)
+ | not (isOpenSynTyCon con) -- don't match oversaturated family apps
= do { (args', cargs, args_eqss, args_skolemss) <- mapAndUnzip4M go args
- ; return (mkTyConApp con args',
- mkTyConApp con cargs,
- concat args_eqss,
- unionVarSets args_skolemss)
+ ; if null args_eqss
+ then -- unchanged, keep the old type with folded synonyms
+ return (ty, ty, [], emptyVarSet)
+ else
+ return (mkTyConApp con args',
+ mkTyConApp con cargs,
+ concat args_eqss,
+ unionVarSets args_skolemss)
}
-- function type => flatten subtypes
-- NB: Special cased for efficiency - could be handled as type application
- go (FunTy ty_l ty_r)
+ go ty@(FunTy ty_l ty_r)
= do { (ty_l', co_l, eqs_l, skolems_l) <- go ty_l
; (ty_r', co_r, eqs_r, skolems_r) <- go ty_r
- ; return (mkFunTy ty_l' ty_r',
- mkFunTy co_l co_r,
- eqs_l ++ eqs_r,
- skolems_l `unionVarSet` skolems_r)
+ ; if null eqs_l && null eqs_r
+ then -- unchanged, keep the old type with folded synonyms
+ return (ty, ty, [], emptyVarSet)
+ else
+ return (mkFunTy ty_l' ty_r',
+ mkFunTy co_l co_r,
+ eqs_l ++ eqs_r,
+ skolems_l `unionVarSet` skolems_r)
}
-- type application => flatten subtypes
- go (AppTy ty_l ty_r)
--- | Just (ty_l, ty_r) <- repSplitAppTy_maybe ty
+ go ty
+ | Just (ty_l, ty_r) <- repSplitAppTy_maybe ty
+ -- need to use the smart split as ty may be an
+ -- oversaturated family application
= do { (ty_l', co_l, eqs_l, skolems_l) <- go ty_l
; (ty_r', co_r, eqs_r, skolems_r) <- go ty_r
- ; return (mkAppTy ty_l' ty_r',
- mkAppTy co_l co_r,
- eqs_l ++ eqs_r,
- skolems_l `unionVarSet` skolems_r)
+ ; if null eqs_l && null eqs_r
+ then -- unchanged, keep the old type with folded synonyms
+ return (ty, ty, [], emptyVarSet)
+ else
+ return (mkAppTy ty_l' ty_r',
+ mkAppTy co_l co_r,
+ eqs_l ++ eqs_r,
+ skolems_l `unionVarSet` skolems_r)
}
-- forall type => panic if the body contains a type family
go (PredTy _)
= panic "TcTyFuns.flattenType: unexpected PredType"
+ go _ = panic "TcTyFuns: suppress bogus warning"
+
adjustCoercions :: EqInstCo -- coercion of original equality
- -> Coercion -- coercion witnessing the rewrite
+ -> Coercion -- coercion witnessing the left rewrite
+ -> Coercion -- coercion witnessing the right rewrite
-> (Type, Type) -- types of flattened equality
-> [RewriteInst] -- equalities from flattening
-> TcM (EqInstCo, -- coercion for flattened equality
-- Depending on whether we flattened a local or wanted equality, that equality's
-- coercion and that of the new equalities produced during flattening are
-- adjusted .
-adjustCoercions co rewriteCo eqTys all_eqs
-
+adjustCoercions (Left cotv) co1 co2 (ty_l, ty_r) all_eqs
-- wanted => generate a fresh coercion variable for the flattened equality
- | isWantedCo co
- = do { co' <- mkRightTransEqInstCo co rewriteCo eqTys
- ; return (co', all_eqs)
+ = do { cotv' <- newMetaCoVar ty_l ty_r
+ ; writeMetaTyVar cotv $
+ (co1 `mkTransCoercion` TyVarTy cotv' `mkTransCoercion` co2)
+ ; return (Left cotv', all_eqs)
}
+adjustCoercions co@(Right _) _co1 _co2 _eqTys all_eqs
-- local => turn all new equalities into locals and update (but not zonk)
-- the skolem
- | otherwise
= do { all_eqs' <- mapM wantedToLocal all_eqs
; return (co, all_eqs')
}
where
loc = tci_loc dict
--- gamma :: Fam args ~ alpha
--- => alpha :: Fam args ~ alpha, with alpha := Fam args
+-- gamma ::^l Fam args ~ alpha
+-- => gamma ::^w Fam args ~ alpha, with alpha := Fam args & gamma := Fam args
-- (the update of alpha will not be apparent during propagation, as we
-- never follow the indirections of meta variables; it will be revealed
-- when the equality is zonked)
+--
+-- NB: It's crucial to update *both* alpha and gamma, as gamma may already
+-- have escaped into some other coercions during normalisation.
+--
wantedToLocal :: RewriteInst -> TcM RewriteInst
wantedToLocal eq@(RewriteFam {rwi_fam = fam,
rwi_args = args,
- rwi_right = alphaTy@(TyVarTy alpha)})
+ rwi_right = TyVarTy alpha,
+ rwi_co = Left gamma})
= do { writeMetaTyVar alpha (mkTyConApp fam args)
- ; return $ eq {rwi_co = mkGivenCo alphaTy}
+ ; writeMetaTyVar gamma (mkTyConApp fam args)
+ ; return $ eq {rwi_co = mkGivenCo $ mkTyVarTy gamma}
}
wantedToLocal _ = panic "TcTyFuns.wantedToLocal"
\end{code}
}
where
substRules eq1 eq2
- = do { -- try the SubstFam rule
- optEqs <- applySubstFam eq1 eq2
+ = do {traceTc $ hang (ptext (sLit "Trying subst rules with"))
+ 4 (ppr eq1 $$ ppr eq2)
+
+ -- try the SubstFam rule
+ ; optEqs <- applySubstFam eq1 eq2
; case optEqs of
Just (eqs, skolems) -> return (eqs, [], skolems)
Nothing -> do
-> TcM (Maybe ([RewriteInst], TyVarSet))
applySubstFam eq1@(RewriteFam {rwi_fam = fam1, rwi_args = args1})
eq2@(RewriteFam {rwi_fam = fam2, rwi_args = args2})
+
+ -- rule matches => rewrite
| fam1 == fam2 && tcEqTypes args1 args2 &&
(isWantedRewriteInst eq2 || not (isWantedRewriteInst eq1))
--- !!!TODO: tcEqTypes is insufficient as it does not look through type synonyms
--- !!!Check whether anything breaks by making tcEqTypes look through synonyms.
--- !!!Should be ok and we don't want three type equalities.
= do { co2' <- mkRightTransEqInstCo co2 co1 (lhs, rhs)
; eq2' <- deriveEqInst eq2 lhs rhs co2'
; liftM Just $ normEqInst eq2'
}
+
+ -- rule would match with eq1 and eq2 swapped => put eq2 into todo list
+ | fam1 == fam2 && tcEqTypes args1 args2 &&
+ (isWantedRewriteInst eq1 || not (isWantedRewriteInst eq2))
+ = return $ Just ([eq2], emptyVarSet)
+
where
lhs = rwi_right eq1
rhs = rwi_right eq2
co1 = eqInstCoType (rwi_co eq1)
co2 = rwi_co eq2
+
applySubstFam _ _ = return Nothing
\end{code}
-> TcM (Maybe ([RewriteInst], TyVarSet))
applySubstVarVar eq1@(RewriteVar {rwi_var = tv1})
eq2@(RewriteVar {rwi_var = tv2})
+
+ -- rule matches => rewrite
| tv1 == tv2 &&
(isWantedRewriteInst eq2 || not (isWantedRewriteInst eq1))
= do { co2' <- mkRightTransEqInstCo co2 co1 (lhs, rhs)
; eq2' <- deriveEqInst eq2 lhs rhs co2'
; liftM Just $ normEqInst eq2'
}
+
+ -- rule would match with eq1 and eq2 swapped => put eq2 into todo list
+ | tv1 == tv2 &&
+ (isWantedRewriteInst eq1 || not (isWantedRewriteInst eq2))
+ = return $ Just ([eq2], emptyVarSet)
+
where
lhs = rwi_right eq1
rhs = rwi_right eq2
co1 = eqInstCoType (rwi_co eq1)
co2 = rwi_co eq2
+
applySubstVarVar _ _ = return Nothing
\end{code}
\begin{code}
applySubstVarFam :: RewriteInst -> RewriteInst -> TcM (Maybe RewriteInst)
+
+ -- rule matches => rewrite
applySubstVarFam eq1@(RewriteVar {rwi_var = tv1})
eq2@(RewriteFam {rwi_fam = fam2, rwi_args = args2})
| tv1 `elemVarSet` tyVarsOfTypes args2
rhs2 = rwi_right eq2
co1 = eqInstCoType (rwi_co eq1)
co2 = rwi_co eq2
+
+ -- rule would match with eq1 and eq2 swapped => put eq2 into todo list
+applySubstVarFam (RewriteFam {rwi_args = args1})
+ eq2@(RewriteVar {rwi_var = tv2})
+ | tv2 `elemVarSet` tyVarsOfTypes args1
+ = return $ Just eq2
+
applySubstVarFam _ _ = return Nothing
\end{code}
We also apply the same substitutions to the local and wanted class and IP
dictionaries.
-NB: Given that we apply the substitution corresponding to a single equality
-exhaustively, before turning to the next, and because we eliminate recursive
-equalities, all opportunities for subtitution will have been exhausted after
-we have considered each equality once.
+The treatment of flexibles in wanteds is quite subtle. We absolutely want to
+substitute them into right-hand sides of equalities, to avoid getting two
+competing instantiations for a type variables; e.g., consider
+
+ F s ~ alpha, alpha ~ t
+
+If we don't substitute `alpha ~ t', we may instantiate t with `F s' instead.
+This would be bad as `F s' is less useful, eg, as an argument to a class
+constraint.
+
+However, there is no reason why we would want to *substitute* `alpha ~ t' into a
+class constraint. We rather wait until `alpha' is instantiated to `t` and
+save the extra dictionary binding that substitution would introduce.
+Moreover, we may substitute wanted equalities only into wanted dictionaries.
+
+NB:
+* Given that we apply the substitution corresponding to a single equality
+ exhaustively, before turning to the next, and because we eliminate recursive
+ equalities, all opportunities for subtitution will have been exhausted after
+ we have considered each equality once.
\begin{code}
substitute :: [RewriteInst] -- equalities
where
subst [] res binds locals wanteds
= return (res, binds, locals, wanteds)
+
subst (eq@(RewriteVar {rwi_var = tv, rwi_right = ty, rwi_co = co}):eqs)
res binds locals wanteds
- = do { traceTc $ ptext (sLit "TcTyFuns.substitute:") <+> ppr tv <+>
- ptext (sLit "->") <+> ppr ty
+ = do { traceTc $ ptext (sLit "TcTyFuns.substitute:") <+> ppr eq
+
; let coSubst = zipOpenTvSubst [tv] [eqInstCoType co]
tySubst = zipOpenTvSubst [tv] [ty]
- ; eqs' <- mapM (substEq eq coSubst tySubst) eqs
- ; res' <- mapM (substEq eq coSubst tySubst) res
- ; (lbinds, locals') <- mapAndUnzipM
- (substDict eq coSubst tySubst False)
- locals
- ; (wbinds, wanteds') <- mapAndUnzipM
- (substDict eq coSubst tySubst True)
- wanteds
+ ; eqs' <- mapM (substEq eq coSubst tySubst) eqs
+ ; res' <- mapM (substEq eq coSubst tySubst) res
+
+ -- only susbtitute local equalities into local dictionaries
+ ; (lbinds, locals') <- if not (isWantedCo co)
+ then
+ mapAndUnzipM
+ (substDict eq coSubst tySubst False)
+ locals
+ else
+ return ([], locals)
+
+ -- flexible tvs in wanteds will be instantiated anyway, there is
+ -- no need to substitute them into dictionaries
+ ; (wbinds, wanteds') <- if not (isMetaTyVar tv && isWantedCo co)
+ then
+ mapAndUnzipM
+ (substDict eq coSubst tySubst True)
+ wanteds
+ else
+ return ([], wanteds)
+
; let binds' = unionManyBags $ binds : lbinds ++ wbinds
; subst eqs' (eq:res') binds' locals' wanteds'
}
-- We have, co :: tv ~ ty
-- => apply [ty/tv] to right-hand side of eq2
-- (but only if tv actually occurs in the right-hand side of eq2)
- substEq (RewriteVar {rwi_var = tv, rwi_right = ty, rwi_co = co})
+ substEq (RewriteVar {rwi_var = tv, rwi_right = ty})
coSubst tySubst eq2
| tv `elemVarSet` tyVarsOfType (rwi_right eq2)
= do { let co1Subst = mkSymCoercion $ substTy coSubst (rwi_right eq2)
-- We have, co :: tv ~ ty
-- => apply [ty/tv] to dictionary predicate
-- (but only if tv actually occurs in the predicate)
- substDict (RewriteVar {rwi_var = tv, rwi_right = ty, rwi_co = co})
- coSubst tySubst isWanted dict
+ substDict (RewriteVar {rwi_var = tv}) coSubst tySubst isWanted dict
| isClassDict dict
, tv `elemVarSet` tyVarsOfPred (tci_pred dict)
- = do { let co1Subst = mkSymCoercion $
- PredTy (substPred coSubst (tci_pred dict))
+ = do { let co1Subst = PredTy (substPred coSubst (tci_pred dict))
pred' = substPred tySubst (tci_pred dict)
; (dict', binds) <- mkDictBind dict isWanted co1Subst pred'
; return (binds, dict')
For any *wanted* variable equality of the form co :: alpha ~ t or co :: a ~
alpha, we instantiate alpha with t or a, respectively, and set co := id.
Return all remaining wanted equalities. The Boolean result component is True
-if at least one instantiation of a flexible was performed.
+if at least one instantiation of a flexible that is *not* a skolem from
+flattening was performed.
+
+We need to instantiate all flexibles that arose as skolems during flattening
+of wanteds before we instantiate any other flexibles. Consider F delta ~
+alpha, F alpha ~ delta, where alpha is a skolem and delta a free flexible. We
+need to produce F (F delta) ~ delta (and not F (F alpha) ~ alpha). Otherwise,
+we may wrongly claim to having performed an improvement, which can lead to
+non-termination of the combined class-family solver.
\begin{code}
-instantiateAndExtract :: [RewriteInst] -> TcM ([Inst], Bool)
-instantiateAndExtract eqs
- = do { let wanteds = filter (isWantedCo . rwi_co) eqs
- ; wanteds' <- mapM inst wanteds
- ; let residuals = catMaybes wanteds'
- improved = length wanteds /= length residuals
+instantiateAndExtract :: [RewriteInst] -> Bool -> TyVarSet -> TcM ([Inst], Bool)
+instantiateAndExtract eqs localsEmpty skolems
+ = do { traceTc $ hang (ptext (sLit "instantiateAndExtract:"))
+ 4 (ppr eqs $$ ppr skolems)
+ -- start by *only* instantiating skolem flexibles from flattening
+ ; unflat_wanteds <- liftM catMaybes $
+ mapM (inst (`elemVarSet` skolems)) wanteds
+ -- only afterwards instantiate free flexibles
+ ; residuals <- liftM catMaybes $ mapM (inst (const True)) unflat_wanteds
+ ; let improvement = length residuals < length unflat_wanteds
; residuals' <- mapM rewriteInstToInst residuals
- ; return (residuals', improved)
+ ; return (residuals', improvement)
}
where
- inst eq@(RewriteVar {rwi_var = tv1, rwi_right = ty2, rwi_co = co})
-
- -- co :: alpha ~ t
- | isMetaTyVar tv1
- = doInst (rwi_swapped eq) tv1 ty2 co eq
+ wanteds = filter (isWantedCo . rwi_co) eqs
+ checkingMode = length eqs > length wanteds || not localsEmpty
+ -- no local equalities or dicts => checking mode
+
+ -- co :: alpha ~ t or co :: a ~ alpha
+ inst mayInst eq@(RewriteVar {rwi_var = tv1, rwi_right = ty2, rwi_co = co})
+ = do { flexi_tv1 <- isFlexible mayInst tv1
+ ; maybe_flexi_tv2 <- isFlexibleTy mayInst ty2
+ ; case (flexi_tv1, maybe_flexi_tv2) of
+ (True, _)
+ -> -- co :: alpha ~ t
+ doInst (rwi_swapped eq) tv1 ty2 co eq
+ (False, Just tv2)
+ -> -- co :: a ~ alpha
+ doInst (not $ rwi_swapped eq) tv2 (mkTyVarTy tv1) co eq
+ _ -> return $ Just eq
+ }
- -- co :: a ~ alpha
+ -- co :: F args ~ alpha, and we are in checking mode (ie, no locals)
+ inst mayInst eq@(RewriteFam {rwi_fam = fam, rwi_args = args,
+ rwi_right = ty2, rwi_co = co})
| Just tv2 <- tcGetTyVar_maybe ty2
, isMetaTyVar tv2
- = doInst (not $ rwi_swapped eq) tv2 (mkTyVarTy tv1) co eq
-
- inst eq = return $ Just eq
+ , mayInst tv2 && (checkingMode || tv2 `elemVarSet` skolems)
+ -- !!!FIXME: this is too liberal, even if tv2 is in
+ -- skolems we shouldn't instantiate if tvs occurs
+ -- in other equalities that may propagate it into the
+ -- environment
+ = doInst (not $ rwi_swapped eq) tv2 (mkTyConApp fam args) co eq
+
+ inst _mayInst eq = return $ Just eq
+
+ -- tv is a meta var and not filled
+ isFlexible mayInst tv
+ | isMetaTyVar tv && mayInst tv = liftM isFlexi $ readMetaTyVar tv
+ | otherwise = return False
+
+ -- type is a tv that is a meta var and not filled
+ isFlexibleTy mayInst ty
+ | Just tv <- tcGetTyVar_maybe ty = do {flexi <- isFlexible mayInst tv
+ ; if flexi then return $ Just tv
+ else return Nothing
+ }
+ | otherwise = return Nothing
doInst _swapped _tv _ty (Right ty) _eq
= pprPanic "TcTyFuns.doInst: local eq: " (ppr ty)
; uMeta swapped tv lookupTV ty cotv
}
where
- -- meta variable has been filled already
- -- => ignore (must be a skolem that was introduced by flattening locals)
- uMeta _swapped _tv (IndirectTv _) _ty _cotv
- = return Nothing
+ -- Try to fill in a meta variable. There is *no* need to consider
+ -- reorienting the underlying equality; `checkOrientation' makes sure
+ -- that we get variable-variable equalities only in the appropriate
+ -- orientation.
+ --
+ uMeta :: Bool -- is this a swapped equality?
+ -> TcTyVar -- tyvar to instantiate
+ -> LookupTyVarResult -- lookup result of that tyvar
+ -> TcType -- to to instantiate tyvar with
+ -> TcTyVar -- coercion tyvar of current equality
+ -> TcM (Maybe RewriteInst) -- returns the original equality if
+ -- the tyvar could not be instantiated,
+ -- and hence, the equality must be kept
- -- type variable meets type variable
- -- => check that tv2 hasn't been updated yet and choose which to update
- uMeta swapped tv1 (DoneTv details1) (TyVarTy tv2) cotv
- | tv1 == tv2
- = panic "TcTyFuns.uMeta: normalisation shouldn't allow x ~ x"
-
- | otherwise
- = do { lookupTV2 <- lookupTcTyVar tv2
- ; case lookupTV2 of
- IndirectTv ty ->
- uMeta swapped tv1 (DoneTv details1) ty cotv
- DoneTv details2 ->
- uMetaVar swapped tv1 details1 tv2 details2 cotv
+ -- meta variable has been filled already
+ -- => keep the equality
+ uMeta _swapped tv (IndirectTv fill_ty) ty _cotv
+ = do { traceTc $
+ ptext (sLit "flexible") <+> ppr tv <+>
+ ptext (sLit "already filled with") <+> ppr fill_ty <+>
+ ptext (sLit "meant to fill with") <+> ppr ty
+ ; return $ Just eq
}
- ------ Beyond this point we know that ty2 is not a type variable
-
- -- signature skolem meets non-variable type
+ -- signature skolem
-- => cannot update (retain the equality)!
uMeta _swapped _tv (DoneTv (MetaTv (SigTv _) _)) _non_tv_ty _cotv
= return $ Just eq
+ -- type variable meets type variable
+ -- => `checkOrientation' already ensures that it is fine to instantiate
+ -- tv1 with tv2, but chase tv2's instantiations if necessary
+ -- NB: tv's instantiations won't alter the orientation in which we
+ -- want to instantiate as they either constitute a family
+ -- application or are themselves due to a properly oriented
+ -- instantiation
+ uMeta swapped tv1 details1@(DoneTv (MetaTv _ ref)) ty@(TyVarTy tv2) cotv
+ = do { lookupTV2 <- lookupTcTyVar tv2
+ ; case lookupTV2 of
+ IndirectTv ty' ->
+ uMeta swapped tv1 details1 ty' cotv
+ DoneTv _ ->
+ uMetaInst swapped tv1 ref ty cotv
+ }
+
-- updatable meta variable meets non-variable type
-- => occurs check, monotype check, and kinds match check, then update
uMeta swapped tv (DoneTv (MetaTv _ ref)) non_tv_ty cotv
+ = uMetaInst swapped tv ref non_tv_ty cotv
+
+ uMeta _ _ _ _ _ = panic "TcTyFuns.uMeta"
+
+ -- We know `tv' can be instantiated; check that `ty' is alright for
+ -- instantiating `tv' with and then do it; otherwise, return the original
+ -- equality.
+ uMetaInst swapped tv ref ty cotv
= do { -- occurs + monotype check
- ; mb_ty' <- checkTauTvUpdate tv non_tv_ty
+ ; mb_ty' <- checkTauTvUpdate tv ty
; case mb_ty' of
Nothing ->
- -- normalisation shouldn't leave families in non_tv_ty
- panic "TcTyFuns.uMeta: unexpected synonym family"
+ -- there may be a family in non_tv_ty due to an unzonked,
+ -- but updated skolem for a local equality
+ return $ Just eq
Just ty' ->
do { checkUpdateMeta swapped tv ref ty' -- update meta var
; writeMetaTyVar cotv ty' -- update co var
; return Nothing
}
}
-
- uMeta _ _ _ _ _ = panic "TcTyFuns.uMeta"
-
- -- uMetaVar: unify two type variables
- -- meta variable meets skolem
- -- => just update
- uMetaVar swapped tv1 (MetaTv _ ref) tv2 (SkolemTv _) cotv
- = do { checkUpdateMeta swapped tv1 ref (mkTyVarTy tv2)
- ; writeMetaTyVar cotv (mkTyVarTy tv2)
- ; return Nothing
- }
-
- -- meta variable meets meta variable
- -- => be clever about which of the two to update
- -- (from TcUnify.uUnfilledVars minus boxy stuff)
- uMetaVar swapped tv1 (MetaTv info1 ref1) tv2 (MetaTv info2 ref2) cotv
- = do { case (info1, info2) of
- -- Avoid SigTvs if poss
- (SigTv _, _ ) | k1_sub_k2 -> update_tv2
- (_, SigTv _) | k2_sub_k1 -> update_tv1
-
- (_, _) | 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
- -- Update the variable with least kind info
- -- See notes on type inference in Kind.lhs
- -- The "nicer to" part only applies if the two kinds are the same,
- -- so we can choose which to do.
-
- ; writeMetaTyVar cotv (mkTyVarTy tv2)
- ; return Nothing
- }
- where
- -- Kinds should be guaranteed ok at this point
- update_tv1 = updateMeta tv1 ref1 (mkTyVarTy tv2)
- update_tv2 = updateMeta tv2 ref2 (mkTyVarTy tv1)
-
- kind_err = addErrCtxtM (unifyKindCtxt swapped tv1 (mkTyVarTy tv2)) $
- unifyKindMisMatch k1 k2
-
- k1 = tyVarKind tv1
- k2 = tyVarKind tv2
- k1_sub_k2 = k1 `isSubKind` k2
- k2_sub_k1 = k2 `isSubKind` k1
-
- 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
-
- uMetaVar _ _ _ _ _ _ = panic "uMetaVar"
\end{code}
= do { env0 <- tcInitTidyEnv
; ty1 <- zonkTcType ty1
; ty2 <- zonkTcType ty2
+ ; let (env1 , tidy_ty1) = tidyOpenType env0 ty1
+ (_env2, tidy_ty2) = tidyOpenType env1 ty2
; addWarnTc $ hang (ptext (sLit "Dropping loopy given equality"))
- 2 (ppr ty1 <+> text "~" <+> ppr ty2)
+ 2 (quotes (ppr tidy_ty1 <+> text "~" <+> ppr tidy_ty2))
}
\end{code}
projects / ghc-hetmet.git / blobdiff