+Normalisation of type terms relative to type instances as well as
+normalisation and entailment checking of equality constraints.
\begin{code}
module TcTyFuns (
- tcNormalizeFamInst,
+ tcNormaliseFamInst,
- normaliseGivens, normaliseGivenDicts,
- normaliseWanteds, normaliseWantedDicts,
- solveWanteds,
+ normaliseGivenEqs, normaliseGivenDicts,
+ normaliseWantedEqs, normaliseWantedDicts,
+ solveWantedEqs,
substEqInDictInsts,
- addBind -- should not be here
+ -- errors
+ eqInstMisMatch, misMatchMsg,
) where
#include "HsVersions.h"
-import HsSyn
-
+--friends
import TcRnMonad
import TcEnv
import Inst
import TcType
import TcMType
+
+-- GHC
import Coercion
-import TypeRep ( Type(..) )
-import TyCon
-import Var ( isTcTyVar )
import Type
+import TypeRep ( Type(..) )
+import TyCon
+import HsSyn
+import VarEnv
+import Var
+import Name
import Bag
import Outputable
import SrcLoc ( Located(..) )
import Maybes
+-- standard
import Data.List
import Control.Monad (liftM)
\end{code}
Normalise 'Type's and 'PredType's by unfolding type family applications where
possible (ie, we treat family instances as a TRS). Also zonk meta variables.
- tcNormalizeFamInst ty = (co, ty')
+ tcNormaliseFamInst ty = (co, ty')
then co : ty ~ ty'
\begin{code}
-tcNormalizeFamInst :: TcType -> TcM (CoercionI, TcType)
-tcNormalizeFamInst = tcGenericNormalizeFamInst tcUnfoldSynFamInst
+tcNormaliseFamInst :: TcType -> TcM (CoercionI, TcType)
+tcNormaliseFamInst = tcGenericNormaliseFamInst tcUnfoldSynFamInst
-tcNormalizeFamInstPred :: TcPredType -> TcM (CoercionI, TcPredType)
-tcNormalizeFamInstPred = tcGenericNormalizeFamInstPred tcUnfoldSynFamInst
+tcNormaliseFamInstPred :: TcPredType -> TcM (CoercionI, TcPredType)
+tcNormaliseFamInstPred = tcGenericNormaliseFamInstPred tcUnfoldSynFamInst
\end{code}
-Normalise a type relative to the rewrite rule implied by one EqInst.
+Normalise a type relative to the rewrite rule implied by one EqInst or an
+already unpacked EqInst (ie, an equality rewrite rule).
\begin{code}
-tcEqInstNormalizeFamInst :: Inst -> TcType -> TcM (CoercionI, Type)
-tcEqInstNormalizeFamInst inst = ASSERT( isEqInst inst )
- tcGenericNormalizeFamInst matchInst
+-- Rewrite by EqInst
+tcEqInstNormaliseFamInst :: Inst -> TcType -> TcM (CoercionI, Type)
+tcEqInstNormaliseFamInst inst =
+ ASSERT( isEqInst inst )
+ tcEqRuleNormaliseFamInst (pat, rhs, co)
where
pat = eqInstLeftTy inst
rhs = eqInstRightTy inst
- co = eitherEqInst inst TyVarTy id
- --
- matchInst ty | pat `tcEqType` ty = return $ Just (rhs, co)
- | otherwise = return $ Nothing
+ co = eqInstType inst
+
+-- Rewrite by equality rewrite rule
+tcEqRuleNormaliseFamInst :: (TcType, -- rewrite rule lhs
+ TcType, -- rewrite rule rhs
+ TcType) -- coercion witnessing the rewrite rule
+ -> TcType -- type to rewrite
+ -> TcM (CoercionI, Type)
+tcEqRuleNormaliseFamInst (pat, rhs, co) ty
+ = tcGenericNormaliseFamInst matchEqRule ty
+ where
+ matchEqRule sty | pat `tcEqType` sty = return $ Just (rhs, co)
+ | otherwise = return $ Nothing
\end{code}
Generic normalisation of 'Type's and 'PredType's; ie, walk the type term and
apply the normalisation function gives as the first argument to every TyConApp
and every TyVarTy subterm.
- tcGenericNormalizeFamInst fun ty = (co, ty')
+ tcGenericNormaliseFamInst fun ty = (co, ty')
then co : ty ~ ty'
This function is (by way of using smart constructors) careful to ensure that
good error messages, callers should discard ty' in favour of ty in this case.
\begin{code}
-tcGenericNormalizeFamInst :: (TcType -> TcM (Maybe (TcType, Coercion)))
+tcGenericNormaliseFamInst :: (TcType -> TcM (Maybe (TcType, Coercion)))
-- what to do with type functions and tyvars
-> TcType -- old type
-> TcM (CoercionI, TcType) -- (coercion, new type)
-tcGenericNormalizeFamInst fun ty
- | Just ty' <- tcView ty = tcGenericNormalizeFamInst fun ty'
-tcGenericNormalizeFamInst fun (TyConApp tyCon tys)
- = do { (cois, ntys) <- mapAndUnzipM (tcGenericNormalizeFamInst fun) tys
+tcGenericNormaliseFamInst fun ty
+ | Just ty' <- tcView ty = tcGenericNormaliseFamInst fun ty'
+tcGenericNormaliseFamInst fun (TyConApp tyCon tys)
+ = do { (cois, ntys) <- mapAndUnzipM (tcGenericNormaliseFamInst fun) tys
; let tycon_coi = mkTyConAppCoI tyCon ntys cois
- ; maybe_ty_co <- fun (TyConApp tyCon ntys) -- use normalised args!
+ ; maybe_ty_co <- fun (mkTyConApp tyCon ntys) -- use normalised args!
; case maybe_ty_co of
-- a matching family instance exists
Just (ty', co) ->
do { let first_coi = mkTransCoI tycon_coi (ACo co)
- ; (rest_coi, nty) <- tcGenericNormalizeFamInst fun ty'
+ ; (rest_coi, nty) <- tcGenericNormaliseFamInst fun ty'
; let fix_coi = mkTransCoI first_coi rest_coi
; return (fix_coi, nty)
}
-- no matching family instance exists
-- we do not do anything
- Nothing -> return (tycon_coi, TyConApp tyCon ntys)
+ Nothing -> return (tycon_coi, mkTyConApp tyCon ntys)
}
-tcGenericNormalizeFamInst fun (AppTy ty1 ty2)
- = do { (coi1,nty1) <- tcGenericNormalizeFamInst fun ty1
- ; (coi2,nty2) <- tcGenericNormalizeFamInst fun ty2
- ; return (mkAppTyCoI nty1 coi1 nty2 coi2, AppTy nty1 nty2)
+tcGenericNormaliseFamInst fun (AppTy ty1 ty2)
+ = do { (coi1,nty1) <- tcGenericNormaliseFamInst fun ty1
+ ; (coi2,nty2) <- tcGenericNormaliseFamInst fun ty2
+ ; return (mkAppTyCoI nty1 coi1 nty2 coi2, mkAppTy nty1 nty2)
}
-tcGenericNormalizeFamInst fun (FunTy ty1 ty2)
- = do { (coi1,nty1) <- tcGenericNormalizeFamInst fun ty1
- ; (coi2,nty2) <- tcGenericNormalizeFamInst fun ty2
- ; return (mkFunTyCoI nty1 coi1 nty2 coi2, FunTy nty1 nty2)
+tcGenericNormaliseFamInst fun (FunTy ty1 ty2)
+ = do { (coi1,nty1) <- tcGenericNormaliseFamInst fun ty1
+ ; (coi2,nty2) <- tcGenericNormaliseFamInst fun ty2
+ ; return (mkFunTyCoI nty1 coi1 nty2 coi2, mkFunTy nty1 nty2)
}
-tcGenericNormalizeFamInst fun (ForAllTy tyvar ty1)
- = do { (coi,nty1) <- tcGenericNormalizeFamInst fun ty1
- ; return (mkForAllTyCoI tyvar coi,ForAllTy tyvar nty1)
+tcGenericNormaliseFamInst fun (ForAllTy tyvar ty1)
+ = do { (coi,nty1) <- tcGenericNormaliseFamInst fun ty1
+ ; return (mkForAllTyCoI tyvar coi, mkForAllTy tyvar nty1)
}
-tcGenericNormalizeFamInst fun (NoteTy note ty1)
- = do { (coi,nty1) <- tcGenericNormalizeFamInst fun ty1
- ; return (mkNoteTyCoI note coi,NoteTy note nty1)
+tcGenericNormaliseFamInst fun (NoteTy note ty1)
+ = do { (coi,nty1) <- tcGenericNormaliseFamInst fun ty1
+ ; return (mkNoteTyCoI note coi, NoteTy note nty1)
}
-tcGenericNormalizeFamInst fun ty@(TyVarTy tv)
+tcGenericNormaliseFamInst fun ty@(TyVarTy tv)
| isTcTyVar tv
- = do { traceTc (text "tcGenericNormalizeFamInst" <+> ppr ty)
+ = do { traceTc (text "tcGenericNormaliseFamInst" <+> ppr ty)
; res <- lookupTcTyVar tv
; case res of
DoneTv _ ->
; case maybe_ty' of
Nothing -> return (IdCo, ty)
Just (ty', co1) ->
- do { (coi2, ty'') <- tcGenericNormalizeFamInst fun ty'
+ do { (coi2, ty'') <- tcGenericNormaliseFamInst fun ty'
; return (ACo co1 `mkTransCoI` coi2, ty'')
}
}
- IndirectTv ty' -> tcGenericNormalizeFamInst fun ty'
+ IndirectTv ty' -> tcGenericNormaliseFamInst fun ty'
}
| otherwise
= return (IdCo, ty)
-tcGenericNormalizeFamInst fun (PredTy predty)
- = do { (coi, pred') <- tcGenericNormalizeFamInstPred fun predty
+tcGenericNormaliseFamInst fun (PredTy predty)
+ = do { (coi, pred') <- tcGenericNormaliseFamInstPred fun predty
; return (coi, PredTy pred') }
---------------------------------
-tcGenericNormalizeFamInstPred :: (TcType -> TcM (Maybe (TcType,Coercion)))
+tcGenericNormaliseFamInstPred :: (TcType -> TcM (Maybe (TcType,Coercion)))
-> TcPredType
-> TcM (CoercionI, TcPredType)
-tcGenericNormalizeFamInstPred fun (ClassP cls tys)
- = do { (cois, tys')<- mapAndUnzipM (tcGenericNormalizeFamInst fun) tys
+tcGenericNormaliseFamInstPred fun (ClassP cls tys)
+ = do { (cois, tys')<- mapAndUnzipM (tcGenericNormaliseFamInst fun) tys
; return (mkClassPPredCoI cls tys' cois, ClassP cls tys')
}
-tcGenericNormalizeFamInstPred fun (IParam ipn ty)
- = do { (coi, ty') <- tcGenericNormalizeFamInst fun ty
+tcGenericNormaliseFamInstPred fun (IParam ipn ty)
+ = do { (coi, ty') <- tcGenericNormaliseFamInst fun ty
; return $ (mkIParamPredCoI ipn coi, IParam ipn ty')
}
-tcGenericNormalizeFamInstPred fun (EqPred ty1 ty2)
- = do { (coi1, ty1') <- tcGenericNormalizeFamInst fun ty1
- ; (coi2, ty2') <- tcGenericNormalizeFamInst fun ty2
+tcGenericNormaliseFamInstPred fun (EqPred ty1 ty2)
+ = do { (coi1, ty1') <- tcGenericNormaliseFamInst fun ty1
+ ; (coi2, ty2') <- tcGenericNormaliseFamInst fun ty2
; return (mkEqPredCoI ty1' coi1 ty2' coi2, EqPred ty1' ty2') }
\end{code}
%************************************************************************
%* *
-\section{Normalisation of Given Dictionaries}
+\section{Normalisation of equality constraints}
+%* *
+%************************************************************************
+
+Note [Inconsistencies in equality constraints]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We guarantee that we raise an error if we discover any inconsistencies (i.e.,
+equalities that if presented to the unifer in TcUnify would result in an
+error) during normalisation of wanted constraints. This is especially so that
+we don't solve wanted constraints under an inconsistent given set. In
+particular, we don't want to permit signatures, such as
+
+ bad :: (Int ~ Bool => Int) -> a -> a
+
+\begin{code}
+normaliseGivenEqs :: [Inst] -> TcM ([Inst], TcM ())
+normaliseGivenEqs givens
+ = do { traceTc (text "normaliseGivenEqs <-" <+> ppr givens)
+ ; (result, deSkolem) <-
+ rewriteToFixedPoint (Just ("(SkolemOccurs)", skolemOccurs))
+ [ ("(ZONK)", dontRerun $ zonkInsts)
+ , ("(TRIVIAL)", dontRerun $ trivialRule)
+ , ("(DECOMP)", decompRule)
+ , ("(TOP)", topRule)
+ , ("(SUBST)", substRule) -- incl. occurs check
+ ] givens
+ ; traceTc (text "normaliseGivenEqs ->" <+> ppr result)
+ ; return (result, deSkolem)
+ }
+\end{code}
+
+\begin{code}
+normaliseWantedEqs :: [Inst] -> TcM [Inst]
+normaliseWantedEqs insts
+ = do { traceTc (text "normaliseWantedEqs <-" <+> ppr insts)
+ ; result <- liftM fst $ rewriteToFixedPoint Nothing
+ [ ("(ZONK)", dontRerun $ zonkInsts)
+ , ("(TRIVIAL)", dontRerun $ trivialRule)
+ , ("(DECOMP)", decompRule)
+ , ("(TOP)", topRule)
+ , ("(UNIFY)", unifyMetaRule) -- incl. occurs check
+ , ("(SUBST)", substRule) -- incl. occurs check
+ ] insts
+ ; traceTc (text "normaliseWantedEqs ->" <+> ppr result)
+ ; return result
+ }
+\end{code}
+
+
+%************************************************************************
+%* *
+\section{Solving of wanted constraints with respect to a given set}
+%* *
+%************************************************************************
+
+The set of given equalities must have been normalised already.
+
+\begin{code}
+solveWantedEqs :: [Inst] -- givens
+ -> [Inst] -- wanteds
+ -> TcM [Inst] -- irreducible wanteds
+solveWantedEqs givens wanteds
+ = do { traceTc $ text "solveWantedEqs <-" <+> ppr wanteds <+> text "with" <+>
+ ppr givens
+ ; result <- liftM fst $ rewriteToFixedPoint Nothing
+ [ ("(ZONK)", dontRerun $ zonkInsts)
+ , ("(TRIVIAL)", dontRerun $ trivialRule)
+ , ("(DECOMP)", decompRule)
+ , ("(TOP)", topRule)
+ , ("(GIVEN)", substGivens givens) -- incl. occurs check
+ , ("(UNIFY)", unifyMetaRule) -- incl. occurs check
+ ] wanteds
+ ; traceTc (text "solveWantedEqs ->" <+> ppr result)
+ ; return result
+ }
+ where
+ -- Use `substInst' with every given on all the wanteds.
+ substGivens :: [Inst] -> [Inst] -> TcM ([Inst], Bool)
+ substGivens [] wanteds = return (wanteds, False)
+ substGivens (g:gs) wanteds
+ = do { (wanteds1, changed1) <- substGivens gs wanteds
+ ; (wanteds2, changed2) <- substInst g wanteds1
+ ; return (wanteds2, changed1 || changed2)
+ }
+\end{code}
+
+
+%************************************************************************
+%* *
+\section{Normalisation of non-equality dictionaries}
%* *
%************************************************************************
-- Fals <=> they are given
-> TcM ([Inst],TcDictBinds)
normalise_dicts given_eqs dicts is_wanted
- = do { traceTc $ text "normaliseGivenDicts <-" <+> ppr dicts <+>
+ = do { traceTc $ text "normalise???Dicts <-" <+> ppr dicts <+>
text "with" <+> ppr given_eqs
; (dicts0, binds0) <- normaliseInsts is_wanted dicts
; (dicts1, binds1) <- substEqInDictInsts given_eqs dicts0
%************************************************************************
%* *
-\section{Normalisation of wanteds constraints}
+\section{Normalisation rules and iterative rule application}
%* *
%************************************************************************
+We have three kinds of normalising rewrite rules:
+
+(1) Normalisation rules that rewrite a set of insts and return a flag indicating
+ whether any changes occurred during rewriting that necessitate re-running
+ the current rule set.
+
+(2) Precondition rules that rewrite a set of insts and return a monadic action
+ that reverts the effect of preconditioning.
+
+(3) Idempotent normalisation rules that never require re-running the rule set.
+
\begin{code}
-normaliseWanteds :: [Inst] -> TcM [Inst]
-normaliseWanteds insts
- = do { traceTc (text "normaliseWanteds <-" <+> ppr insts)
- ; result <- liftM fst $ rewriteToFixedPoint Nothing
- [ ("(Occurs)", noChange $ occursCheckInsts)
- , ("(ZONK)", dontRerun $ zonkInsts)
- , ("(TRIVIAL)", trivialInsts)
- -- no `swapInsts'; it messes up error messages and should
- -- not be necessary -=chak
- , ("(DECOMP)", decompInsts)
- , ("(TOP)", topInsts)
- , ("(SUBST)", substInsts)
- , ("(UNIFY)", unifyInsts)
- ] insts
- ; traceTc (text "normaliseWanteds ->" <+> ppr result)
- ; return result
- }
+type RewriteRule = [Inst] -> TcM ([Inst], Bool) -- rewrite, maybe re-run
+type PrecondRule = [Inst] -> TcM ([Inst], TcM ()) -- rewrite, revertable
+type IdemRewriteRule = [Inst] -> TcM [Inst] -- rewrite, don't re-run
+
+type NamedRule = (String, RewriteRule) -- rule with description
+type NamedPreRule = (String, PrecondRule) -- precond with desc
+\end{code}
+
+Template lifting idempotent rules to full rules (which can be put into a rule
+set).
+
+\begin{code}
+dontRerun :: IdemRewriteRule -> RewriteRule
+dontRerun rule insts = liftM addFalse $ rule insts
+ where
+ addFalse x = (x, False)
+\end{code}
+
+The following function applies a set of rewrite rules until a fixed point is
+reached; i.e., none of the `RewriteRule's require re-running the rule set.
+Optionally, there may be a pre-conditing rule that is applied before any other
+rules are applied and before the rule set is re-run.
+
+The result is the set of rewritten (i.e., normalised) insts and, in case of a
+pre-conditing rule, a monadic action that reverts the effects of
+pre-conditioning - specifically, this is removing introduced skolems.
+
+\begin{code}
+rewriteToFixedPoint :: Maybe NamedPreRule -- optional preconditioning rule
+ -> [NamedRule] -- rule set
+ -> [Inst] -- insts to rewrite
+ -> TcM ([Inst], TcM ())
+rewriteToFixedPoint precondRule rules insts
+ = completeRewrite (return ()) precondRule insts
+ where
+ completeRewrite :: TcM () -> Maybe NamedPreRule -> [Inst]
+ -> TcM ([Inst], TcM ())
+ completeRewrite dePrecond (Just (precondName, precond)) insts
+ = do { traceTc $ text precondName <+> text " <- " <+> ppr insts
+ ; (insts', dePrecond') <- precond insts
+ ; traceTc $ text precondName <+> text " -> " <+> ppr insts'
+ ; tryRules (dePrecond >> dePrecond') rules insts'
+ }
+ completeRewrite dePrecond Nothing insts
+ = tryRules dePrecond rules insts
+
+ tryRules dePrecond _ [] = return ([] , dePrecond)
+ tryRules dePrecond [] insts = return (insts, dePrecond)
+ tryRules dePrecond ((name, rule):rules) insts
+ = do { traceTc $ text name <+> text " <- " <+> ppr insts
+ ; (insts', rerun) <- rule insts
+ ; traceTc $ text name <+> text " -> " <+> ppr insts'
+ ; if rerun then completeRewrite dePrecond precondRule insts'
+ else tryRules dePrecond rules insts'
+ }
\end{code}
%************************************************************************
%* *
-\section{Normalisation of givens constraints}
+\section{Different forms of Inst rewrite rules}
%* *
%************************************************************************
-\begin{code}
-normaliseGivens :: [Inst] -> TcM ([Inst], TcM ())
-normaliseGivens givens
- = do { traceTc (text "normaliseGivens <-" <+> ppr givens)
- ; (result, deSkolem) <-
- rewriteToFixedPoint (Just ("(SkolemOccurs)", skolemOccurs))
- [ ("(Occurs)", noChange $ occursCheckInsts)
- , ("(ZONK)", dontRerun $ zonkInsts)
- , ("(TRIVIAL)", trivialInsts)
- , ("(SWAP)", swapInsts)
- , ("(DECOMP)", decompInsts)
- , ("(TOP)", topInsts)
- , ("(SUBST)", substInsts)
- ] givens
- ; traceTc (text "normaliseGivens ->" <+> ppr result)
- ; return (result, deSkolem)
- }
-\end{code}
-
+Splitting of non-terminating given constraints: skolemOccurs
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+This is a preconditioning rule exclusively applied to given constraints.
+Moreover, its rewriting is only temporary, as it is undone by way of
+side-effecting mutable type variables after simplification and constraint
+entailment has been completed.
-This is an (attempt at, yet unproven, an) *unflattened* version of
+This version is an (attempt at, yet unproven, an) *unflattened* version of
the SubstL-Ev completion rule.
-The above rule is essential to catch non-terminating
-rules that cannot be oriented properly, like
+The above rule is essential to catch non-terminating rules that cannot be
+oriented properly, like
F a ~ [G (F a)]
or even
a ~ [G a]
The left-to-right orientiation is not suitable because it does not
-terminate.
-The right-to-left orientation is not suitable because it
+terminate. The right-to-left orientation is not suitable because it
does not have a type-function on the left. This is undesirable because
it would hide information. E.g. assume
+
instance C [x]
+
then rewriting C [G (F a)] to C (F a) is bad because we cannot now
see that the C [x] instance applies.
The rule also caters for badly-oriented rules of the form:
+
F a ~ G (F a)
+
for which other solutions are possible, but this one will do too.
It's behavior is:
+
co : ty1 ~ ty2{F ty1}
>-->
co : ty1 ~ ty2{b}
sym (F co) : F ty2{b} ~ b
where b is a fresh skolem variable
+We also cater for the symmetric situation *if* the rule cannot be used as a
+left-to-right rewrite rule.
+
We also return an action (b := ty1) which is used to eliminate b
after the dust of normalisation with the completed rewrite system
has settled.
}
where
oneSkolemOccurs inst
- | null tysToLiftOut
- = return ([inst], return ())
- | otherwise
- = do { skTvs <- mapM (newMetaTyVar TauTv . typeKind) tysToLiftOut
- ; let skTvs_tysTLO = zip skTvs tysToLiftOut
- insertSkolems = return . replace skTvs_tysTLO
- ; (_, ty2') <- tcGenericNormalizeFamInst insertSkolems ty2
- ; inst' <- mkEqInst (EqPred ty1 ty2') co
- ; (insts, undoSk) <- mapAndUnzipM (mkSkolemInst inst') skTvs_tysTLO
- ; return (inst':insts, sequence_ undoSk)
- }
+ = ASSERT( isEqInst inst )
+ isRewriteRule (eqInstLeftTy inst) (eqInstRightTy inst)
where
- ty1 = eqInstLeftTy inst
- ty2 = eqInstRightTy inst
- co = eqInstCoercion inst
-
- -- all subtypes that are (1) type family instances and (2) contain the
- -- lhs type as part of the type arguments of the type family constructor
- tysToLiftOut = ASSERT( isEqInst inst )
- [mkTyConApp tc tys | (tc, tys) <- tyFamInsts ty2
- , any (ty1 `tcPartOfType`) tys]
-
- replace :: [(TcTyVar, Type)] -> Type -> Maybe (Type, Coercion)
- replace [] _ = Nothing
- replace ((skTv, tyTLO):rest) ty
- | tyTLO `tcEqType` ty = Just (mkTyVarTy skTv, undefined)
- | otherwise = replace rest ty
-
- -- create the EqInst for the equality determining the skolem and a
- -- TcM action undoing the skolem introduction
- mkSkolemInst inst' (skTv, tyTLO)
- = do { (co, tyLiftedOut) <- tcEqInstNormalizeFamInst inst' tyTLO
- ; inst <- mkEqInst (EqPred tyLiftedOut (mkTyVarTy skTv))
- (mkGivenCo $ mkSymCoercion (fromACo co))
- ; return (inst, writeMetaTyVar skTv tyTLO)
+
+ -- look through synonyms
+ isRewriteRule ty1 ty2 | Just ty1' <- tcView ty1 = isRewriteRule ty1' ty2
+ isRewriteRule ty1 ty2 | Just ty2' <- tcView ty2 = isRewriteRule ty1 ty2'
+
+ -- left-to-right rule with type family head
+ isRewriteRule ty1@(TyConApp con _) ty2
+ | isOpenSynTyCon con
+ = breakRecursion ty1 ty2 False -- not swapped
+
+ -- left-to-right rule with type variable head
+ isRewriteRule ty1@(TyVarTy _) ty2
+ = breakRecursion ty1 ty2 False -- not swapped
+
+ -- right-to-left rule with type family head
+ isRewriteRule ty1 ty2@(TyConApp con _)
+ | isOpenSynTyCon con
+ = breakRecursion ty2 ty1 True -- swapped
+
+ -- right-to-left rule with type variable head
+ isRewriteRule ty1 ty2@(TyVarTy _)
+ = breakRecursion ty2 ty1 True -- swapped
+
+ -- this equality is not a rewrite rule => ignore
+ isRewriteRule _ _ = return ([inst], return ())
+
+
+ breakRecursion pat body swapped
+ | null tysToLiftOut
+ = return ([inst], return ())
+ | otherwise
+ = do { skTvs <- mapM (newMetaTyVar TauTv . typeKind) tysToLiftOut
+ ; let skTvs_tysTLO = zip skTvs tysToLiftOut
+ insertSkolems = return . replace skTvs_tysTLO
+ ; (_, body') <- tcGenericNormaliseFamInst insertSkolems body
+ ; inst' <- if swapped then mkEqInst (EqPred body' pat) co
+ else mkEqInst (EqPred pat body') co
+ -- ensure to reconstruct the inst in the
+ -- original orientation
+ ; (insts, undoSk) <- mapAndUnzipM (mkSkolemInst inst')
+ skTvs_tysTLO
+ ; return (inst':insts, sequence_ undoSk)
}
+ where
+ co = eqInstCoercion inst
+
+ -- all subtypes that are (1) type family instances and (2) contain
+ -- the lhs type as part of the type arguments of the type family
+ -- constructor
+ tysToLiftOut = [mkTyConApp tc tys | (tc, tys) <- tyFamInsts body
+ , any (pat `tcPartOfType`) tys]
+
+ replace :: [(TcTyVar, Type)] -> Type -> Maybe (Type, Coercion)
+ replace [] _ = Nothing
+ replace ((skTv, tyTLO):rest) ty
+ | tyTLO `tcEqType` ty = Just (mkTyVarTy skTv, undefined)
+ | otherwise = replace rest ty
+
+ -- create the EqInst for the equality determining the skolem and a
+ -- TcM action undoing the skolem introduction
+ mkSkolemInst inst' (skTv, tyTLO)
+ = do { (co, tyLiftedOut) <- tcEqInstNormaliseFamInst inst' tyTLO
+ ; inst <- mkEqInst (EqPred tyLiftedOut (mkTyVarTy skTv))
+ (mkGivenCo $ mkSymCoercion (fromACo co))
+ ; return (inst, writeMetaTyVar skTv tyTLO)
+ }
\end{code}
-%************************************************************************
-%* *
-\section{Solving of wanted constraints with respect to a given set}
-%* *
-%************************************************************************
+Removal of trivial equalities: trivialRule
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The following rules exploits the reflexivity of equality:
+
+ (Trivial)
+ g1 : t ~ t
+ >-->
+ g1 := t
\begin{code}
-solveWanteds :: [Inst] -- givens
- -> [Inst] -- wanteds
- -> TcM [Inst] -- irreducible wanteds
-solveWanteds givens wanteds
- = do { traceTc $ text "solveWanteds <-" <+> ppr wanteds <+> text "with" <+>
- ppr givens
- ; result <- liftM fst $ rewriteToFixedPoint Nothing
- [ ("(Occurs)", noChange $ occursCheckInsts)
- , ("(TRIVIAL)", trivialInsts)
- , ("(DECOMP)", decompInsts)
- , ("(TOP)", topInsts)
- , ("(GIVEN)", givenInsts givens)
- , ("(UNIFY)", unifyInsts)
- ] wanteds
- ; traceTc (text "solveWanteds ->" <+> ppr result)
- ; return result
- }
+trivialRule :: IdemRewriteRule
+trivialRule insts
+ = liftM catMaybes $ mappM trivial insts
where
- -- Use `substInst' with every given on all the wanteds.
- givenInsts :: [Inst] -> [Inst] -> TcM ([Inst],Bool)
- givenInsts [] wanteds = return (wanteds,False)
- givenInsts (g:gs) wanteds
- = do { (wanteds1, changed1) <- givenInsts gs wanteds
- ; (wanteds2, changed2) <- substInst g wanteds1
- ; return (wanteds2, changed1 || changed2)
+ trivial inst
+ | ASSERT( isEqInst inst )
+ ty1 `tcEqType` ty2
+ = do { eitherEqInst inst
+ (\cotv -> writeMetaTyVar cotv ty1)
+ (\_ -> return ())
+ ; return Nothing
}
+ | otherwise
+ = return $ Just inst
+ where
+ ty1 = eqInstLeftTy inst
+ ty2 = eqInstRightTy inst
\end{code}
-%************************************************************************
-%* *
-\section{Normalisation rules and iterative rule application}
-%* *
-%************************************************************************
-
-We have four kinds of normalising rewrite rules:
-
-(1) Normalisation rules that rewrite a set of insts and return a flag indicating
- whether any changes occurred during rewriting that necessitate re-running
- the current rule set.
+Decomposition of data type constructors: decompRule
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Whenever, the same *data* constructors occurs on both sides of an equality, we
+can decompose as in standard unification.
-(2) Precondition rules that rewrite a set of insts and return a monadic action
- that reverts the effect of preconditioning.
+ (Decomp)
+ g1 : T cs ~ T ds
+ >-->
+ g21 : c1 ~ d1, ..., g2n : cn ~ dn
+ g1 := T g2s
-(3) Idempotent normalisation rules that never require re-running the rule set.
+Works also for the case where T is actually an application of a type family
+constructor to a set of types, provided the applications on both sides of the
+~ are identical; see also Note [OpenSynTyCon app] in TcUnify.
-(4) Checking rule that does not alter the set of insts.
+We guarantee to raise an error for any inconsistent equalities;
+cf Note [Inconsistencies in equality constraints].
\begin{code}
-type RewriteRule = [Inst] -> TcM ([Inst], Bool) -- rewrite, maybe re-run
-type PrecondRule = [Inst] -> TcM ([Inst], TcM ()) -- rewrite, revertable
-type IdemRewriteRule = [Inst] -> TcM [Inst] -- rewrite, don't re-run
-type CheckRule = [Inst] -> TcM () -- check
-
-type NamedRule = (String, RewriteRule) -- rule with description
-type NamedPreRule = (String, PrecondRule) -- precond with desc
+decompRule :: RewriteRule
+decompRule insts
+ = do { (insts, changed) <- mapAndUnzipM decomp insts
+ ; return (concat insts, or changed)
+ }
+ where
+ decomp inst
+ = ASSERT( isEqInst inst )
+ go (eqInstLeftTy inst) (eqInstRightTy inst)
+ where
+ go ty1 ty2
+ | Just ty1' <- tcView ty1 = go ty1' ty2
+ | Just ty2' <- tcView ty2 = go ty1 ty2'
+
+ go (TyConApp con1 tys1) (TyConApp con2 tys2)
+ | con1 == con2 && identicalHead
+ = mkArgInsts (mkTyConApp con1) tys1 tys2
+
+ | con1 /= con2 && not (isOpenSynTyCon con1 || isOpenSynTyCon con2)
+ -- not matching data constructors (of any flavour) are bad news
+ = eqInstMisMatch inst
+ where
+ n = tyConArity con1
+ (idxTys1, _) = splitAt n tys1
+ (idxTys2, _) = splitAt n tys2
+ identicalHead = not (isOpenSynTyCon con1) ||
+ idxTys1 `tcEqTypes` idxTys2
+
+ go (FunTy fun1 arg1) (FunTy fun2 arg2)
+ = mkArgInsts (\[funCo, argCo] -> mkFunTy funCo argCo) [fun1, arg1]
+ [fun2, arg2]
+
+ -- Applications need a bit of care!
+ -- They can match FunTy and TyConApp, so use splitAppTy_maybe
+ go (AppTy s1 t1) ty2
+ | Just (s2, t2) <- tcSplitAppTy_maybe ty2
+ = mkArgInsts (\[s, t] -> mkAppTy s t) [s1, t1] [s2, t2]
+
+ -- Symmetric case
+ go ty1 (AppTy s2 t2)
+ | Just (s1, t1) <- tcSplitAppTy_maybe ty1
+ = mkArgInsts (\[s, t] -> mkAppTy s t) [s1, t1] [s2, t2]
+
+ -- We already covered all the consistent cases of rigid types on both
+ -- sides; so, if we see two rigid types here, we discovered an
+ -- inconsistency.
+ go ty1 ty2
+ | isRigid ty1 && isRigid ty2
+ = eqInstMisMatch inst
+
+ -- We can neither assert consistency nor inconsistency => defer
+ go _ _ = return ([inst], False)
+
+ isRigid (TyConApp con _) = not (isOpenSynTyCon con)
+ isRigid (FunTy _ _) = True
+ isRigid (AppTy _ _) = True
+ isRigid _ = False
+
+ -- Create insts for matching argument positions (ie, the bit after
+ -- '>-->' in the rule description above)
+ mkArgInsts con tys1 tys2
+ = do { cos <- eitherEqInst inst
+ -- old_co := Con1 cos
+ (\old_covar ->
+ do { cotvs <- zipWithM newMetaCoVar tys1 tys2
+ ; let cos = map mkTyVarTy cotvs
+ ; writeMetaTyVar old_covar (con cos)
+ ; return $ map mkWantedCo cotvs
+ })
+ -- co_i := Con_i old_co
+ (\old_co ->
+ return $ map mkGivenCo $
+ mkRightCoercions (length tys1) old_co)
+ ; insts <- zipWithM mkEqInst (zipWith EqPred tys1 tys2) cos
+ ; traceTc (text "decomp identicalHead" <+> ppr insts)
+ ; return (insts, not $ null insts)
+ }
\end{code}
-Templates lifting idempotent and checking rules to full rules (which can be put
-into a rule set).
+
+Rewriting with type instances: topRule
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We use (toplevel) type instances to normalise both sides of equalities.
+
+ (Top)
+ g1 : t ~ s
+ >--> co1 :: t ~ t' / co2 :: s ~ s'
+ g2 : t' ~ s'
+ g1 := co1 * g2 * sym co2
\begin{code}
-dontRerun :: IdemRewriteRule -> RewriteRule
-dontRerun rule insts = liftM addFalse $ rule insts
+topRule :: RewriteRule
+topRule insts
+ = do { (insts, changed) <- mapAndUnzipM top insts
+ ; return (insts, or changed)
+ }
where
- addFalse x = (x, False)
-
-noChange :: CheckRule -> RewriteRule
-noChange rule insts = rule insts >> return (insts, False)
+ top inst
+ = ASSERT( isEqInst inst )
+ do { (coi1, ty1') <- tcNormaliseFamInst ty1
+ ; (coi2, ty2') <- tcNormaliseFamInst ty2
+ ; case (coi1, coi2) of
+ (IdCo, IdCo) -> return (inst, False)
+ _ ->
+ do { wg_co <-
+ eitherEqInst inst
+ -- old_co = co1 * new_co * sym co2
+ (\old_covar ->
+ do { new_cotv <- newMetaCoVar ty1' ty2'
+ ; let new_co = mkTyVarTy new_cotv
+ old_coi = coi1 `mkTransCoI`
+ ACo new_co `mkTransCoI`
+ (mkSymCoI coi2)
+ ; writeMetaTyVar old_covar (fromACo old_coi)
+ ; return $ mkWantedCo new_cotv
+ })
+ -- new_co = sym co1 * old_co * co2
+ (\old_co ->
+ return $
+ mkGivenCo $
+ fromACo $
+ mkSymCoI coi1 `mkTransCoI`
+ ACo old_co `mkTransCoI` coi2)
+ ; new_inst <- mkEqInst (EqPred ty1' ty2') wg_co
+ ; return (new_inst, True)
+ }
+ }
+ where
+ ty1 = eqInstLeftTy inst
+ ty2 = eqInstRightTy inst
\end{code}
-The following function applies a set of rewrite rules until a fixed point is
-reached; i.e., none of the `RewriteRule's require re-running the rule set.
-Optionally, there may be a pre-conditing rule that is applied before any other
-rules are applied and before the rule set is re-run.
-The result is the set of rewritten (i.e., normalised) insts and, in case of a
-pre-conditing rule, a monadic action that reverts the effects of
-pre-conditioning - specifically, this is removing introduced skolems.
+Rewriting with equalities: substRule
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+From a set of insts, use all insts that can be read as rewrite rules to
+rewrite the types in all other insts.
+
+ (Subst)
+ g : F c ~ t,
+ forall g1 : s1{F c} ~ s2{F c}
+ >-->
+ g2 : s1{t} ~ s2{t}
+ g1 := s1{g} * g2 * sym s2{g} <=> g2 := sym s1{g} * g1 * s2{g}
+
+Alternatively, the rewrite rule may have the form (g : a ~ t).
+
+To avoid having to swap rules of the form (g : t ~ F c) and (g : t ~ a),
+where t is neither a variable nor a type family application, we use them for
+rewriting from right-to-left. However, it is crucial to only apply rules
+from right-to-left if they cannot be used left-to-right.
+
+The workhorse is substInst, which performs an occurs check before actually
+using an equality for rewriting. If the type pattern occurs in the type we
+substitute for the pattern, normalisation would diverge.
\begin{code}
-rewriteToFixedPoint :: Maybe NamedPreRule -- optional preconditioning rule
- -> [NamedRule] -- rule set
- -> [Inst] -- insts to rewrite
- -> TcM ([Inst], TcM ())
-rewriteToFixedPoint precondRule rules insts
- = completeRewrite (return ()) precondRule insts
+substRule :: RewriteRule
+substRule insts = tryAllInsts insts []
where
- completeRewrite :: TcM () -> Maybe NamedPreRule -> [Inst]
- -> TcM ([Inst], TcM ())
- completeRewrite dePrecond (Just (precondName, precond)) insts
- = do { (insts', dePrecond') <- precond insts
- ; traceTc $ text precondName <+> ppr insts'
- ; tryRules (dePrecond >> dePrecond') rules insts'
+ -- for every inst check whether it can be used to rewrite the others
+ -- (we make an effort to keep the insts in order; it makes debugging
+ -- easier)
+ tryAllInsts [] triedInsts = return (reverse triedInsts, False)
+ tryAllInsts (inst:insts) triedInsts
+ = do { (insts', changed) <- substInst inst (reverse triedInsts ++ insts)
+ ; if changed then return (insertAt (length triedInsts) inst insts',
+ True)
+ else tryAllInsts insts (inst:triedInsts)
}
- completeRewrite dePrecond Nothing insts
- = tryRules dePrecond rules insts
-
- tryRules dePrecond _ [] = return ([] , dePrecond)
- tryRules dePrecond [] insts = return (insts, dePrecond)
- tryRules dePrecond ((name, rule):rules) insts
- = do { (insts', rerun) <- rule insts
- ; traceTc $ text name <+> ppr insts'
- ; if rerun then completeRewrite dePrecond precondRule insts'
- else tryRules dePrecond rules insts'
+ where
+ insertAt n x xs = let (xs1, xs2) = splitAt n xs
+ in xs1 ++ [x] ++ xs2
+
+-- Use the given inst as a rewrite rule to normalise the insts in the second
+-- argument. Don't do anything if the inst cannot be used as a rewrite rule,
+-- but do apply it right-to-left, if possible, and if it cannot be used
+-- left-to-right.
+--
+substInst :: Inst -> [Inst] -> TcM ([Inst], Bool)
+substInst inst insts
+ = ASSERT( isEqInst inst )
+ go (eqInstLeftTy inst) (eqInstRightTy inst) (eqInstType inst)
+ where
+ -- 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
+
+ -- rewrite type family applications
+ go ty1@(TyConApp con _) ty2 co
+ | isOpenSynTyCon con
+ = substEquality (ty1, ty2, co) insts
+
+ -- rewrite skolems
+ go ty1@(TyVarTy tv) ty2 co
+ | isSkolemTyVar tv
+ = substEquality (ty1, ty2, co) insts
+
+ -- rewrite type family applications from right-to-left, only after
+ -- having checked whether we can work left-to-right
+ go ty1 ty2@(TyConApp con _) co
+ | isOpenSynTyCon con
+ = substEquality (ty2, ty1, mkSymCoercion co) insts
+
+ -- rewrite skolems from right-to-left, only after having checked
+ -- whether we can work left-to-right
+ go ty1 ty2@(TyVarTy tv) co
+ | isSkolemTyVar tv
+ = substEquality (ty2, ty1, mkSymCoercion co) insts
+
+ go _ _ _ = return (insts, False)
+
+ substEquality :: (TcType, -- rewrite rule lhs
+ TcType, -- rewrite rule rhs
+ TcType) -- coercion witnessing the rewrite rule
+ -> [Inst] -- insts to rewrite
+ -> TcM ([Inst], Bool)
+ substEquality eqRule@(pat, rhs, _) insts
+ | pat `tcPartOfType` rhs -- occurs check!
+ = occurCheckErr pat rhs
+ | otherwise
+ = do { (insts', changed) <- mapAndUnzipM substOne insts
+ ; return (insts', or changed)
}
+ where
+ substOne inst
+ = ASSERT( isEqInst inst )
+ do { (coi1, ty1') <- tcEqRuleNormaliseFamInst eqRule ty1
+ ; (coi2, ty2') <- tcEqRuleNormaliseFamInst eqRule ty2
+ ; case (coi1, coi2) of
+ (IdCo, IdCo) -> return (inst, False)
+ _ ->
+ do { gw_co <-
+ eitherEqInst inst
+ -- old_co := co1 * new_co * sym co2
+ (\old_covar ->
+ do { new_cotv <- newMetaCoVar ty1' ty2'
+ ; let new_co = mkTyVarTy new_cotv
+ old_coi = coi1 `mkTransCoI`
+ ACo new_co `mkTransCoI`
+ (mkSymCoI coi2)
+ ; writeMetaTyVar old_covar (fromACo old_coi)
+ ; return $ mkWantedCo new_cotv
+ })
+ -- new_co := sym co1 * old_co * co2
+ (\old_co ->
+ return $
+ mkGivenCo $
+ fromACo $
+ mkSymCoI coi1 `mkTransCoI`
+ ACo old_co `mkTransCoI` coi2)
+ ; new_inst <- mkEqInst (EqPred ty1' ty2') gw_co
+ ; return (new_inst, True)
+ }
+ }
+ where
+ ty1 = eqInstLeftTy inst
+ ty2 = eqInstRightTy inst
\end{code}
-%************************************************************************
-%* *
-\section{Different forms of Inst rewritings}
-%* *
-%************************************************************************
+Instantiate meta variables: unifyMetaRule
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+If an equality equates a meta type variable with a type, we simply instantiate
+the meta variable.
-Rewrite schemata applied by way of eq_rewrite and friends.
+ (UnifyMeta)
+ g : alpha ~ t
+ >-->
+ alpha := t
+ g := t
-\begin{code}
+Meta variables can only appear in wanted constraints, and this rule should
+only be applied to wanted constraints. We also know that t definitely is
+distinct from alpha (as the trivialRule) has been run on the insts beforehand.
- -- (Trivial)
- -- g1 : t ~ t
- -- >-->
- -- g1 := t
- --
-trivialInsts :: RewriteRule
-trivialInsts []
- = return ([],False)
-trivialInsts (i@(EqInst {}):is)
- = do { (is',changed)<- trivialInsts is
- ; if tcEqType ty1 ty2
- then do { eitherEqInst i
- (\covar -> writeMetaTyVar covar ty1)
- (\_ -> return ())
- ; return (is',True)
- }
- else return (i:is',changed)
- }
- where
- ty1 = eqInstLeftTy i
- ty2 = eqInstRightTy i
-trivialInsts _ = panic "TcTyFuns.trivialInsts: not EqInst"
-
--- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-swapInsts :: RewriteRule
--- All the inputs and outputs are equalities
-swapInsts insts
- = do { (insts', changeds) <- mapAndUnzipM swapInst insts
- ; return (insts', or changeds)
- }
+NB: We cannot assume that meta tyvars are empty. They may have been updated
+by another inst in the currently processed wanted list. We need to be very
+careful when updateing type variables (see TcUnify.uUnfilledVar), but at least
+we know that we have no boxes. It's unclear that it would be an advantage to
+common up the code in TcUnify and the code below. Firstly, we don't want
+calls to TcUnify.defer_unification here, and secondly, TcUnify import the
+current module, so we would have to move everything here (Yuk!) or to
+TcMType. Besides, the code here is much simpler due to the lack of boxes.
- -- (Swap)
- -- g1 : c ~ F d
- -- >-->
- -- g2 : F d ~ c
- -- g1 := sym g2
- -- where c isn't a function call
- -- and
- --
- -- g1 : c ~ a
- -- >-->
- -- g2 : a ~ c
- -- g1 := sym g2
- -- where c isn't a function call or other variable
-swapInst :: Inst -> TcM (Inst, Bool)
-swapInst i@(EqInst {})
- = go ty1 ty2
- where
- ty1 = eqInstLeftTy i
- ty2 = eqInstRightTy i
- go ty1 ty2 | Just ty1' <- tcView ty1
- = go ty1' ty2
- go ty1 ty2 | Just ty2' <- tcView ty2
- = go ty1 ty2'
- go (TyConApp tyCon _) _ | isOpenSynTyCon tyCon
- = return (i,False)
- -- we should swap!
- go ty1 ty2@(TyConApp tyCon _)
- | isOpenSynTyCon tyCon
- = actual_swap ty1 ty2
- go ty1@(TyConApp _ _) ty2@(TyVarTy _)
- = actual_swap ty1 ty2
- go _ _ = return (i,False)
-
- actual_swap ty1 ty2 = do { wg_co <- eitherEqInst i
- -- old_co := sym new_co
- (\old_covar ->
- do { new_cotv <- newMetaTyVar TauTv (mkCoKind ty2 ty1)
- ; let new_co = TyVarTy new_cotv
- ; writeMetaTyVar old_covar (mkCoercion symCoercionTyCon [new_co])
- ; return $ mkWantedCo new_cotv
- })
- -- new_co := sym old_co
- (\old_co -> return $ mkGivenCo $ mkCoercion symCoercionTyCon [old_co])
- ; new_inst <- mkEqInst (EqPred ty2 ty1) wg_co
- ; return (new_inst,True)
- }
-swapInst _ = panic "TcTyFuns.swapInst: not EqInst"
-
--- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-decompInsts :: RewriteRule
-decompInsts insts = do { (insts,bs) <- mapAndUnzipM decompInst insts
- ; return (concat insts,or bs)
- }
-
- -- (Decomp)
- -- g1 : T cs ~ T ds
- -- >-->
- -- g21 : c1 ~ d1, ..., g2n : cn ~ dn
- -- g1 := T g2s
- --
- -- Works also for the case where T is actually an application of a
- -- type family constructor to a set of types, provided the
- -- applications on both sides of the ~ are identical;
- -- see also Note [OpenSynTyCon app] in TcUnify
- --
-decompInst :: Inst -> TcM ([Inst],Bool)
-decompInst i@(EqInst {})
- = go ty1 ty2
- where
- ty1 = eqInstLeftTy i
- ty2 = eqInstRightTy i
- go ty1 ty2
- | Just ty1' <- tcView ty1 = go ty1' ty2
- | Just ty2' <- tcView ty2 = go ty1 ty2'
-
- go ty1@(TyConApp con1 tys1) ty2@(TyConApp con2 tys2)
- | con1 == con2 && identicalHead
- = do { cos <- eitherEqInst i
- -- old_co := Con1 cos
- (\old_covar ->
- do { cotvs <- zipWithM (\t1 t2 ->
- newMetaTyVar TauTv
- (mkCoKind t1 t2))
- tys1 tys2
- ; let cos = map TyVarTy cotvs
- ; writeMetaTyVar old_covar (TyConApp con1 cos)
- ; return $ map mkWantedCo cotvs
- })
- -- co_i := Con_i old_co
- (\old_co -> return $
- map mkGivenCo $
- mkRightCoercions (length tys1) old_co)
- ; insts <- zipWithM mkEqInst (zipWith EqPred tys1 tys2) cos
- ; traceTc (text "decomp identicalHead" <+> ppr insts)
- ; return (insts, not $ null insts)
- }
- | con1 /= con2 && not (isOpenSynTyCon con1 || isOpenSynTyCon con2)
- -- not matching data constructors (of any flavour) are bad news
- = do { env0 <- tcInitTidyEnv
- ; let (env1, tidy_ty1) = tidyOpenType env0 ty1
- (env2, tidy_ty2) = tidyOpenType env1 ty2
- extra = sep [ppr tidy_ty1, char '~', ppr tidy_ty2]
- msg =
- ptext SLIT("Unsolvable equality constraint:")
- ; failWithTcM (env2, hang msg 2 extra)
- }
+\begin{code}
+unifyMetaRule :: RewriteRule
+unifyMetaRule insts
+ = do { (insts', changed) <- mapAndUnzipM unifyMeta insts
+ ; return (concat insts', or changed)
+ }
+ where
+ unifyMeta inst
+ = ASSERT( isEqInst inst )
+ go (eqInstLeftTy inst) (eqInstRightTy inst)
+ (fromWantedCo "unifyMetaRule" $ eqInstCoercion inst)
where
- n = tyConArity con1
- (idxTys1, _) = splitAt n tys1
- (idxTys2, _) = splitAt n tys2
- identicalHead = not (isOpenSynTyCon con1) ||
- idxTys1 `tcEqTypes` idxTys2
-
- go _ _ = return ([i], False)
-decompInst _ = panic "TcTyFuns.decompInst: not EqInst"
-
--- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-topInsts :: RewriteRule
-topInsts insts
- = do { (insts,bs) <- mapAndUnzipM topInst insts
- ; return (insts,or bs)
- }
-
- -- (Top)
- -- g1 : t ~ s
- -- >--> co1 :: t ~ t' / co2 :: s ~ s'
- -- g2 : t' ~ s'
- -- g1 := co1 * g2 * sym co2
-topInst :: Inst -> TcM (Inst,Bool)
-topInst i@(EqInst {})
- = do { (coi1,ty1') <- tcNormalizeFamInst ty1
- ; (coi2,ty2') <- tcNormalizeFamInst ty2
- ; case (coi1,coi2) of
- (IdCo,IdCo) ->
- return (i,False)
- _ ->
- do { wg_co <- eitherEqInst i
- -- old_co = co1 * new_co * sym co2
- (\old_covar ->
- do { new_cotv <- newMetaTyVar TauTv (mkCoKind ty1 ty2)
- ; let new_co = TyVarTy new_cotv
- ; let old_coi = coi1 `mkTransCoI` ACo new_co `mkTransCoI` (mkSymCoI coi2)
- ; writeMetaTyVar old_covar (fromACo old_coi)
- ; return $ mkWantedCo new_cotv
- })
- -- new_co = sym co1 * old_co * co2
- (\old_co -> return $ mkGivenCo $ fromACo $ mkSymCoI coi1 `mkTransCoI` ACo old_co `mkTransCoI` coi2)
- ; new_inst <- mkEqInst (EqPred ty1' ty2') wg_co
- ; return (new_inst,True)
- }
- }
- where
- ty1 = eqInstLeftTy i
- ty2 = eqInstRightTy i
-topInst _ = panic "TcTyFuns.topInsts: not EqInst"
-
--- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-substInsts :: RewriteRule
-substInsts insts = substInstsWorker insts []
-
-substInstsWorker :: [Inst] -> [Inst] -> TcM ([Inst],Bool)
-substInstsWorker [] acc
- = return (acc,False)
-substInstsWorker (i:is) acc
- | (TyConApp con _) <- tci_left i, isOpenSynTyCon con
- = do { (is',change) <- substInst i (acc ++ is)
- ; if change
- then return ((i:is'),True)
- else substInstsWorker is (i:acc)
- }
- | (TyVarTy _) <- tci_left i
- = do { (is',change) <- substInst i (acc ++ is)
- ; if change
- then return ((i:is'),True)
- else substInstsWorker is (i:acc)
- }
- | otherwise
- = substInstsWorker is (i:acc)
-
- -- (Subst)
- -- g : F c ~ t,
- -- forall g1 : s1{F c} ~ s2{F c}
- -- >-->
- -- g2 : s1{t} ~ s2{t}
- -- g1 := s1{g} * g2 * sym s2{g} <=> g2 := sym s1{g} * g1 * s2{g}
-substInst :: Inst -> [Inst] -> TcM ([Inst], Bool)
-substInst _inst [] = return ([],False)
-substInst inst (i@(EqInst {tci_left = ty1, tci_right = ty2}):is)
- = do { (is',changed) <- substInst inst is
- ; (coi1,ty1') <- normalise ty1
- ; (coi2,ty2') <- normalise ty2
- ; case (coi1,coi2) of
- (IdCo,IdCo) ->
- return (i:is',changed)
- _ ->
- do { gw_co <- eitherEqInst i
- -- old_co := co1 * new_co * sym co2
- (\old_covar ->
- do { new_cotv <- newMetaTyVar TauTv (mkCoKind ty1' ty2')
- ; let new_co = TyVarTy new_cotv
- ; let old_coi = coi1 `mkTransCoI` ACo new_co `mkTransCoI` (mkSymCoI coi2)
- ; writeMetaTyVar old_covar (fromACo old_coi)
- ; return $ mkWantedCo new_cotv
- })
- -- new_co := sym co1 * old_co * co2
- (\old_co -> return $ mkGivenCo $ fromACo $ (mkSymCoI coi1) `mkTransCoI` ACo old_co `mkTransCoI` coi2)
- ; new_inst <- mkEqInst (EqPred ty1' ty2') gw_co
- ; return (new_inst:is',True)
- }
- }
- where
- normalise = tcEqInstNormalizeFamInst inst
-substInst _ _ = panic "TcTyFuns.substInst: not EqInst"
-
--- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-unifyInsts :: RewriteRule
-unifyInsts insts
- = do { (insts',changeds) <- mapAndUnzipM unifyInst insts
- ; return (concat insts',or changeds)
- }
+ go ty1 ty2 cotv
+ | Just ty1' <- tcView ty1 = go ty1' ty2 cotv
+ | Just ty2' <- tcView ty2 = go ty1 ty2' cotv
+
+ | TyVarTy tv1 <- ty1
+ , isMetaTyVar tv1 = do { lookupTV <- lookupTcTyVar tv1
+ ; uMeta False tv1 lookupTV ty2 cotv
+ }
+ | TyVarTy tv2 <- ty2
+ , isMetaTyVar tv2 = do { lookupTV <- lookupTcTyVar tv2
+ ; uMeta True tv2 lookupTV ty1 cotv
+ }
+ | otherwise = return ([inst], False)
+
+ -- meta variable has been filled already
+ -- => ignore this inst (we'll come around again, after zonking)
+ uMeta _swapped _tv (IndirectTv _) _ty _cotv
+ = return ([inst], False)
+
+ -- signature skolem meets non-variable type
+ -- => cannot update!
+ uMeta _swapped _tv (DoneTv (MetaTv (SigTv _) _)) ty _cotv
+ | not $ isTyVarTy ty
+ = return ([inst], False)
+
+ -- 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
+ = 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
+ }
+
+ -- updatable meta variable meets non-variable type
+ -- => occurs check, monotype check, and kinds match check, then update
+ uMeta swapped tv (DoneTv (MetaTv _ ref)) ty cotv
+ = do { ty' <- checkTauTvUpdate tv ty -- occurs + monotype check
+ ; checkUpdateMeta swapped tv ref ty' -- update meta var
+ ; writeMetaTyVar cotv ty' -- update the co var
+ ; return ([], True)
+ }
+
+ uMeta _ _ _ _ _ = panic "uMeta"
+
+ -- 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 ([], True)
+ }
+
+ -- 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 ([], True)
+ }
+ where
+ -- Kinds should be guaranteed ok at this point
+ update_tv1 = updateMeta tv1 ref1 (mkTyVarTy tv2)
+ update_tv2 = updateMeta tv2 ref2 (mkTyVarTy tv1)
- -- (UnifyMeta)
- -- g : alpha ~ t
- -- >-->
- -- alpha := t
- -- g := t
- --
- -- TOMDO: you should only do this for certain `meta' type variables
-unifyInst :: Inst -> TcM ([Inst], Bool)
-unifyInst i@(EqInst {tci_left = ty1, tci_right = ty2})
- | TyVarTy tv1 <- ty1, isMetaTyVar tv1 = go ty2 tv1
- | TyVarTy tv2 <- ty2, isMetaTyVar tv2 = go ty1 tv2
- | otherwise = return ([i],False)
- where go ty tv
- = do { let cotv = fromWantedCo "unifyInst" $ eqInstCoercion i
- ; writeMetaTyVar tv ty -- alpha := t
- ; writeMetaTyVar cotv ty -- g := t
- ; return ([],True)
- }
-unifyInst _ = panic "TcTyFuns.unifyInst: not EqInst"
-
--- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-occursCheckInsts :: CheckRule
-occursCheckInsts insts = mappM_ occursCheckInst insts
-
-
- -- (OccursCheck)
- -- t ~ s[T t]
- -- >-->
- -- fail
- --
-occursCheckInst :: Inst -> TcM ()
-occursCheckInst (EqInst {tci_left = ty1, tci_right = ty2})
- = go ty2
- where
- check ty = if ty `tcEqType` ty1
- then occursError
- else go ty
-
- go (TyConApp con tys) = if isOpenSynTyCon con then return () else mappM_ check tys
- go (FunTy arg res) = mappM_ check [arg,res]
- go (AppTy fun arg) = mappM_ check [fun,arg]
- go _ = return ()
-
- occursError = do { env0 <- tcInitTidyEnv
- ; let (env1, tidy_ty1) = tidyOpenType env0 ty1
- (env2, tidy_ty2) = tidyOpenType env1 ty2
- extra = sep [ppr tidy_ty1, char '~', ppr tidy_ty2]
- ; failWithTcM (env2, hang msg 2 extra)
- }
- where msg = ptext SLIT("Occurs check: cannot construct the infinite type")
-occursCheckInst _ = panic "TcTyFuns.occursCheckInst: not eqInst"
+ 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}
+
+%************************************************************************
+%* *
+\section{Normalisation of Insts}
+%* *
+%************************************************************************
+
Normalises a set of dictionaries relative to a set of given equalities (which
are interpreted as rewrite rules). We only consider given equalities of the
form
- F ts ~ t
+ F ts ~ t or a ~ t
where F is a type family.
substEqInDictInsts :: [Inst] -- given equalities (used as rewrite rules)
-> [Inst] -- dictinaries to be normalised
-> TcM ([Inst], TcDictBinds)
-substEqInDictInsts eq_insts insts
- = do { traceTc (text "substEqInDictInst <-" <+> ppr insts)
- ; result <- foldlM rewriteWithOneEquality (insts, emptyBag) eq_insts
- ; traceTc (text "substEqInDictInst ->" <+> ppr result)
- ; return result
+substEqInDictInsts eqInsts dictInsts
+ = do { traceTc (text "substEqInDictInst <-" <+> ppr dictInsts)
+ ; dictInsts' <-
+ foldlM rewriteWithOneEquality (dictInsts, emptyBag) eqInsts
+ ; traceTc (text "substEqInDictInst ->" <+> ppr dictInsts')
+ ; return dictInsts'
}
where
- -- (1) Given equality of form 'F ts ~ t': use for rewriting
- rewriteWithOneEquality (insts, dictBinds)
- inst@(EqInst {tci_left = pattern,
- tci_right = target})
- | isOpenSynTyConApp pattern
- = do { (insts', moreDictBinds) <- genericNormaliseInsts True {- wanted -}
- applyThisEq insts
- ; return (insts', dictBinds `unionBags` moreDictBinds)
+ -- (1) Given equality of form 'F ts ~ t' or 'a ~ t': use for rewriting
+ rewriteWithOneEquality (dictInsts, dictBinds)
+ eqInst@(EqInst {tci_left = pattern,
+ tci_right = target})
+ | isOpenSynTyConApp pattern || isTyVarTy pattern
+ = do { (dictInsts', moreDictBinds) <-
+ genericNormaliseInsts True {- wanted -} applyThisEq dictInsts
+ ; return (dictInsts', dictBinds `unionBags` moreDictBinds)
}
where
- applyThisEq = tcGenericNormalizeFamInstPred (return . matchResult)
+ applyThisEq = tcGenericNormaliseFamInstPred (return . matchResult)
-- rewrite in case of an exact match
- matchResult ty | tcEqType pattern ty = Just (target, eqInstType inst)
+ matchResult ty | tcEqType pattern ty = Just (target, eqInstType eqInst)
| otherwise = Nothing
-- (2) Given equality has the wrong form: ignore
- rewriteWithOneEquality (insts, dictBinds) _not_a_rewrite_rule
- = return (insts, dictBinds)
+ rewriteWithOneEquality (dictInsts, dictBinds) _not_a_rewrite_rule
+ = return (dictInsts, dictBinds)
\end{code}
-%************************************************************************
-%* *
- Normalisation of Insts
-%* *
-%************************************************************************
Take a bunch of Insts (not EqInsts), and normalise them wrt the top-level
type-function equations, where
= True, (binds + norm_insts) defines insts (wanteds)
= False, (binds + insts) defines norm_insts (givens)
+Ie, in the case of normalising wanted dictionaries, we use the normalised
+dictionaries to define the originally wanted ones. However, in the case of
+given dictionaries, we use the originally given ones to define the normalised
+ones.
+
\begin{code}
normaliseInsts :: Bool -- True <=> wanted insts
-> [Inst] -- wanted or given insts
- -> TcM ([Inst], TcDictBinds) -- normalized insts and bindings
+ -> TcM ([Inst], TcDictBinds) -- normalised insts and bindings
normaliseInsts isWanted insts
- = genericNormaliseInsts isWanted tcNormalizeFamInstPred insts
+ = genericNormaliseInsts isWanted tcNormaliseFamInstPred insts
genericNormaliseInsts :: Bool -- True <=> wanted insts
-> (TcPredType -> TcM (CoercionI, TcPredType))
-- how to normalise
-> [Inst] -- wanted or given insts
- -> TcM ([Inst], TcDictBinds) -- normalized insts & binds
+ -> TcM ([Inst], TcDictBinds) -- normalised insts & binds
genericNormaliseInsts isWanted fun insts
= do { (insts', binds) <- mapAndUnzipM (normaliseOneInst isWanted fun) insts
; return (insts', unionManyBags binds)
normaliseOneInst isWanted fun
dict@(Dict {tci_pred = pred,
tci_loc = loc})
- = do { traceTc (text "genericNormaliseInst 1")
+ = do { traceTc $ text "genericNormaliseInst <-" <+> ppr dict
; (coi, pred') <- fun pred
- ; traceTc (text "genericNormaliseInst 2")
; case coi of
- IdCo -> return (dict, emptyBag)
+ IdCo ->
+ do { traceTc $ text "genericNormaliseInst ->" <+> ppr dict
+ ; return (dict, emptyBag)
+ }
-- don't use pred' in this case; otherwise, we get
-- more unfolded closed type synonyms in error messages
ACo co ->
; let (target_dict, source_dict, st_co)
| isWanted = (dict, dict', mkSymCoercion co)
| otherwise = (dict', dict, co)
- -- if isWanted
- -- co :: dict ~ dict'
- -- hence dict = dict' `cast` sym co
- -- else
- -- co :: dict ~ dict'
- -- hence dict' = dict `cast` co
+ -- we have
+ -- co :: dict ~ dict'
+ -- hence, if isWanted
+ -- dict = dict' `cast` sym co
+ -- else
+ -- dict' = dict `cast` co
expr = HsVar $ instToId source_dict
cast_expr = HsWrap (WpCo st_co) expr
rhs = L (instLocSpan loc) cast_expr
- binds = mkBind target_dict rhs
+ binds = instToDictBind target_dict rhs
-- return the new inst
- ; return (dict', binds)
+ ; traceTc $ text "genericNormaliseInst ->" <+> ppr dict'
+ ; return (dict', binds)
}
}
- -- TOMDO: treat other insts appropriately
+ -- TOMDO: What do we have to do about ImplicInst, Method, and LitInst??
normaliseOneInst _isWanted _fun inst
= do { inst' <- zonkInst inst
; return (inst', emptyBag)
}
+\end{code}
+
+
+%************************************************************************
+%* *
+\section{Errors}
+%* *
+%************************************************************************
+
+The infamous couldn't match expected type soandso against inferred type
+somethingdifferent message.
-addBind :: Bag (LHsBind TcId) -> Inst -> LHsExpr TcId -> Bag (LHsBind TcId)
-addBind binds inst rhs = binds `unionBags` mkBind inst rhs
+\begin{code}
+eqInstMisMatch :: Inst -> TcM a
+eqInstMisMatch inst
+ = ASSERT( isEqInst inst )
+ do { (env, msg) <- misMatchMsg ty_act ty_exp
+ ; setErrCtxt ctxt $
+ failWithTcM (env, msg)
+ }
+ where
+ ty_act = eqInstLeftTy inst
+ ty_exp = eqInstRightTy inst
+ InstLoc _ _ ctxt = instLoc inst
+
+-----------------------
+misMatchMsg :: TcType -> TcType -> TcM (TidyEnv, SDoc)
+-- Generate the message when two types fail to match,
+-- going to some trouble to make it helpful.
+-- The argument order is: actual type, expected type
+misMatchMsg ty_act ty_exp
+ = do { env0 <- tcInitTidyEnv
+ ; ty_exp <- zonkTcType ty_exp
+ ; ty_act <- zonkTcType ty_act
+ ; (env1, pp_exp, extra_exp) <- ppr_ty env0 ty_exp
+ ; (env2, pp_act, extra_act) <- ppr_ty env1 ty_act
+ ; return (env2,
+ sep [sep [ptext SLIT("Couldn't match expected type") <+> pp_exp,
+ nest 7 $
+ ptext SLIT("against inferred type") <+> pp_act],
+ nest 2 (extra_exp $$ extra_act)]) }
+
+ppr_ty :: TidyEnv -> TcType -> TcM (TidyEnv, SDoc, SDoc)
+ppr_ty env ty
+ = do { let (env1, tidy_ty) = tidyOpenType env ty
+ ; (env2, extra) <- ppr_extra env1 tidy_ty
+ ; return (env2, quotes (ppr tidy_ty), extra) }
+
+-- (ppr_extra env ty) shows extra info about 'ty'
+ppr_extra :: TidyEnv -> Type -> TcM (TidyEnv, SDoc)
+ppr_extra env (TyVarTy tv)
+ | isSkolemTyVar tv || isSigTyVar tv
+ = return (env1, pprSkolTvBinding tv1)
+ where
+ (env1, tv1) = tidySkolemTyVar env tv
-mkBind :: Inst -> LHsExpr TcId -> Bag (LHsBind TcId)
-mkBind inst rhs = unitBag (L (instSpan inst)
- (VarBind (instToId inst) rhs))
+ppr_extra env _ty = return (env, empty) -- Normal case
\end{code}
projects / ghc-hetmet.git / commitdiff