import SrcLoc ( Located(..) )
import Util ( debugIsOn )
import Maybes
+import MonadUtils
import FastString
-- standard
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
+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
; 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
; uMeta swapped tv lookupTV ty cotv
}
where
+ -- 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
+
-- meta variable has been filled already
-- => keep the equality
uMeta _swapped tv (IndirectTv fill_ty) ty _cotv
; return $ Just eq
}
- -- 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"
+ -- signature skolem
+ -- => cannot update (retain the equality)!
+ uMeta _swapped _tv (DoneTv (MetaTv (SigTv _) _)) _non_tv_ty _cotv
+ = return $ Just eq
- | otherwise
+ -- 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 (DoneTv details1) ty cotv
- DoneTv details2 ->
- uMetaVar swapped tv1 details1 tv2 details2 cotv
+ IndirectTv ty' ->
+ uMeta swapped tv1 details1 ty' cotv
+ DoneTv _ ->
+ uMetaInst swapped tv1 ref ty cotv
}
- ------ Beyond this point we know that ty2 is not a type variable
-
- -- signature skolem meets non-variable type
- -- => cannot update (retain the equality)!
- uMeta _swapped _tv (DoneTv (MetaTv (SigTv _) _)) _non_tv_ty _cotv
- = return $ Just eq
-
-- 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 ->
; 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}
projects / ghc-hetmet.git / blobdiff