--
normaliseEqs :: [Inst] -> TcM EqConfig
normaliseEqs eqs
- = do { ASSERTM2( allM isValidWantedEqInst eqs, ppr eqs )
+ = do { ASSERTM2( allM wantedEqInstIsUnsolved eqs, ppr eqs )
; traceTc $ ptext (sLit "Entering normaliseEqs")
; (eqss, skolemss) <- mapAndUnzipM normEqInst eqs
--
normaliseDicts :: Bool -> [Inst] -> TcM EqConfig
normaliseDicts isWanted insts
- = do { traceTc $ ptext (sLit "Entering 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' $$ ppr eqss)
; return $ emptyEqConfig { eqs = concat eqss
, locals = if isWanted then [] else insts'
, wanteds = if isWanted then insts' else []
-- Assert that all cotvs of wanted equalities are still unfilled, and
-- zonk all final insts, to make any improvement visible
- ; ASSERTM2( allM isValidWantedEqInst eqs'', ppr eqs'' )
+ ; ASSERTM2( allM wantedEqInstIsUnsolved eqs'', ppr eqs'' )
; zonked_locals <- zonkInsts locals'
; zonked_wanteds <- zonkInsts (eqs'' ++ wanteds')
; return (zonked_locals, zonked_wanteds, final_binds, improved)
where
loc = tci_loc dict
--- gamma :: Fam args ~ alpha
--- => alpha :: Fam args ~ alpha, with alpha := Fam args
+-- gamma ::^l Fam args ~ alpha
+-- => gamma ::^w Fam args ~ alpha, with alpha := Fam args & gamma := Fam args
-- (the update of alpha will not be apparent during propagation, as we
-- never follow the indirections of meta variables; it will be revealed
-- when the equality is zonked)
+--
+-- NB: It's crucial to update *both* alpha and gamma, as gamma may already
+-- have escaped into some other coercions during normalisation.
+--
wantedToLocal :: RewriteInst -> TcM RewriteInst
wantedToLocal eq@(RewriteFam {rwi_fam = fam,
rwi_args = args,
- rwi_right = alphaTy@(TyVarTy alpha)})
+ rwi_right = TyVarTy alpha,
+ rwi_co = Left gamma})
= do { writeMetaTyVar alpha (mkTyConApp fam args)
- ; return $ eq {rwi_co = mkGivenCo alphaTy}
+ ; writeMetaTyVar gamma (mkTyConApp fam args)
+ ; return $ eq {rwi_co = mkGivenCo $ mkTyVarTy gamma}
}
wantedToLocal _ = panic "TcTyFuns.wantedToLocal"
\end{code}
}
where
substRules eq1 eq2
- = do { -- try the SubstFam rule
- optEqs <- applySubstFam eq1 eq2
+ = do {traceTc $ hang (ptext (sLit "Trying subst rules with"))
+ 4 (ppr eq1 $$ 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
; 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}
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] -> Bool -> TyVarSet -> TcM ([Inst], Bool)
instantiateAndExtract eqs localsEmpty skolems
- = do { results <- mapM inst wanteds
- ; let residuals = [eq | Left eq <- results]
- only_skolems = and [tv `elemVarSet` skolems | Right tv <- results]
+ = 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', not only_skolems)
+ ; return (residuals', improvement)
}
where
wanteds = filter (isWantedCo . rwi_co) eqs
checkingMode = length eqs > length wanteds || not localsEmpty
-- no local equalities or dicts => checking mode
- 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
-
- -- co :: a ~ alpha
- | Just tv2 <- tcGetTyVar_maybe ty2
- , isMetaTyVar tv2
- = doInst (not $ rwi_swapped eq) tv2 (mkTyVarTy tv1) co eq
+ -- 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 :: F args ~ alpha, and we are in checking mode (ie, no locals)
- inst eq@(RewriteFam {rwi_fam = fam, rwi_args = args, rwi_right = ty2,
- rwi_co = co})
+ inst mayInst eq@(RewriteFam {rwi_fam = fam, rwi_args = args,
+ rwi_right = ty2, rwi_co = co})
| Just tv2 <- tcGetTyVar_maybe ty2
, isMetaTyVar tv2
- , checkingMode || tv2 `elemVarSet` skolems
+ , mayInst tv2 && (checkingMode || tv2 `elemVarSet` skolems)
-- !!!TODO: 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 eq = return $ Left 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)
ptext (sLit "flexible") <+> ppr tv <+>
ptext (sLit "already filled with") <+> ppr fill_ty <+>
ptext (sLit "meant to fill with") <+> ppr ty
- ; return $ Left eq
+ ; return $ Just eq
}
-- type variable meets type variable
-- signature skolem meets non-variable type
-- => cannot update (retain the equality)!
uMeta _swapped _tv (DoneTv (MetaTv (SigTv _) _)) _non_tv_ty _cotv
- = return $ Left eq
+ = return $ Just eq
-- updatable meta variable meets non-variable type
-- => occurs check, monotype check, and kinds match check, then update
; 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 $ Right tv
+ ; return Nothing
}
}
uMetaVar swapped tv1 (MetaTv _ ref) tv2 (SkolemTv _) cotv
= do { checkUpdateMeta swapped tv1 ref (mkTyVarTy tv2)
; writeMetaTyVar cotv (mkTyVarTy tv2)
- ; return $ Right tv1
+ ; 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 { tv <- 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 >> return tv1
+ = 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 $ Right tv
+ ; return Nothing
}
where
-- Kinds should be guaranteed ok at this point
update_tv1 = updateMeta tv1 ref1 (mkTyVarTy tv2)
- >> return tv1
update_tv2 = updateMeta tv2 ref2 (mkTyVarTy tv1)
- >> return tv2
kind_err = addErrCtxtM (unifyKindCtxt swapped tv1 (mkTyVarTy tv2)) $
unifyKindMisMatch k1 k2
projects / ghc-hetmet.git / blobdiff