-\section[FamInstEnv]{Type checked family instance declarations}
+%
+% (c) The University of Glasgow 2006
+%
+
+FamInstEnv: Type checked family instance declarations
\begin{code}
+{-# OPTIONS_GHC -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+-- http://hackage.haskell.org/trac/ghc/wiki/WorkingConventions#Warnings
+-- for details
+
module FamInstEnv (
- FamInst(..), famInstTyCon, extractFamInsts,
+ FamInst(..), famInstTyCon, famInstTyVars,
pprFamInst, pprFamInstHdr, pprFamInsts,
- {-famInstHead, mkLocalFamInst, mkImportedFamInst-}
+ famInstHead, mkLocalFamInst, mkImportedFamInst,
- FamInstEnv, emptyFamInstEnv, extendFamInstEnv, extendFamInstEnvList,
+ FamInstEnvs, FamInstEnv, emptyFamInstEnv, emptyFamInstEnvs,
+ extendFamInstEnv, extendFamInstEnvList,
famInstEnvElts, familyInstances,
- {-lookupFamInstEnv-}
+
+ lookupFamInstEnv, lookupFamInstEnvUnify,
+
+ -- Normalisation
+ topNormaliseType
) where
#include "HsVersions.h"
-import TcType ( Type )
-import Type ( TyThing (ATyCon), pprParendType )
-import TyCon ( TyCon, isDataTyCon, isNewTyCon, isSynTyCon,
- tyConName, tyConTyVars, tyConFamInst_maybe )
-import VarSet ( TyVarSet, mkVarSet )
-import Name ( Name, getOccName, NamedThing(..), getSrcLoc )
-import OccName ( parenSymOcc )
-import SrcLoc ( pprDefnLoc )
-import UniqFM ( UniqFM, lookupUFM, emptyUFM, addToUFM_C, eltsUFM )
+import InstEnv
+import Unify
+import TcGadt
+import TcType
+import Type
+import TypeRep
+import TyCon
+import Coercion
+import VarSet
+import Var
+import Name
+import OccName
+import SrcLoc
+import UniqFM
import Outputable
+import Maybes
+import Util
-import Monad ( mzero )
+import Maybe
\end{code}
\begin{code}
data FamInst
= FamInst { fi_fam :: Name -- Family name
+ -- INVARIANT: fi_fam = case tyConFamInst_maybe fi_tycon of
+ -- Just (tc, tys) -> tc
+
+ -- Used for "rough matching"; same idea as for class instances
+ , fi_tcs :: [Maybe Name] -- Top of type args
+ -- INVARIANT: fi_tcs = roughMatchTcs fi_tys
+
+ -- Used for "proper matching"; ditto
, fi_tvs :: TyVarSet -- Template tyvars for full match
, fi_tys :: [Type] -- Full arg types
+ -- INVARIANT: fi_tvs = tyConTyVars fi_tycon
+ -- fi_tys = case tyConFamInst_maybe fi_tycon of
+ -- Just (_, tys) -> tys
, fi_tycon :: TyCon -- Representation tycon
}
famInstTyCon :: FamInst -> TyCon
famInstTyCon = fi_tycon
--- Extract all family instances.
---
-extractFamInsts :: [TyThing] -> [FamInst]
-extractFamInsts tythings
- = do { ATyCon tycon <- tythings
- ; case tyConFamInst_maybe tycon of
- Nothing -> mzero
- Just (fam, tys) ->
- return $ FamInst { fi_fam = tyConName fam
- , fi_tvs = mkVarSet . tyConTyVars $ tycon
- , fi_tys = tys
- , fi_tycon = tycon
- }
- }
+famInstTyVars = fi_tvs
\end{code}
\begin{code}
pprFamInst :: FamInst -> SDoc
pprFamInst famInst
= hang (pprFamInstHdr famInst)
- 2 (ptext SLIT("--") <+> (pprDefnLoc (getSrcLoc famInst)))
+ 2 (ptext SLIT("--") <+> (pprDefnLoc (getSrcSpan famInst)))
pprFamInstHdr :: FamInst -> SDoc
pprFamInstHdr (FamInst {fi_fam = fam, fi_tys = tys, fi_tycon = tycon})
= pprTyConSort <+> pprHead
where
- pprHead = parenSymOcc (getOccName fam) (ppr fam) <+>
- sep (map pprParendType tys)
+ pprHead = pprTypeApp fam (ppr fam) tys
pprTyConSort | isDataTyCon tycon = ptext SLIT("data instance")
| isNewTyCon tycon = ptext SLIT("newtype instance")
| isSynTyCon tycon = ptext SLIT("type instance")
pprFamInsts :: [FamInst] -> SDoc
pprFamInsts finsts = vcat (map pprFamInst finsts)
+
+famInstHead :: FamInst -> ([TyVar], TyCon, [Type])
+famInstHead (FamInst {fi_tycon = tycon})
+ = case tyConFamInst_maybe tycon of
+ Nothing -> panic "FamInstEnv.famInstHead"
+ Just (fam, tys) -> (tyConTyVars tycon, fam, tys)
+
+-- Make a family instance representation from a tycon. This is used for local
+-- instances, where we can safely pull on the tycon.
+--
+mkLocalFamInst :: TyCon -> FamInst
+mkLocalFamInst tycon
+ = case tyConFamInst_maybe tycon of
+ Nothing -> panic "FamInstEnv.mkLocalFamInst"
+ Just (fam, tys) ->
+ FamInst {
+ fi_fam = tyConName fam,
+ fi_tcs = roughMatchTcs tys,
+ fi_tvs = mkVarSet . tyConTyVars $ tycon,
+ fi_tys = tys,
+ fi_tycon = tycon
+ }
+
+-- Make a family instance representation from the information found in an
+-- unterface file. In particular, we get the rough match info from the iface
+-- (instead of computing it here).
+--
+mkImportedFamInst :: Name -> [Maybe Name] -> TyCon -> FamInst
+mkImportedFamInst fam mb_tcs tycon
+ = FamInst {
+ fi_fam = fam,
+ fi_tcs = mb_tcs,
+ fi_tvs = mkVarSet . tyConTyVars $ tycon,
+ fi_tys = case tyConFamInst_maybe tycon of
+ Nothing -> panic "FamInstEnv.mkImportedFamInst"
+ Just (_, tys) -> tys,
+ fi_tycon = tycon
+ }
\end{code}
InstEnv maps a family name to the list of known instances for that family.
\begin{code}
-type FamInstEnv = UniqFM [FamInst] -- Maps a family to its instances
+type FamInstEnv = UniqFM FamilyInstEnv -- Maps a family to its instances
+
+type FamInstEnvs = (FamInstEnv, FamInstEnv)
+ -- External package inst-env, Home-package inst-env
+
+data FamilyInstEnv
+ = FamIE [FamInst] -- The instances for a particular family, in any order
+ Bool -- True <=> there is an instance of form T a b c
+ -- If *not* then the common case of looking up
+ -- (T a b c) can fail immediately
-- INVARIANTS:
-- * The fs_tvs are distinct in each FamInst
-- of a range value of the map (so we can safely unify them)
+emptyFamInstEnvs :: (FamInstEnv, FamInstEnv)
+emptyFamInstEnvs = (emptyFamInstEnv, emptyFamInstEnv)
+
emptyFamInstEnv :: FamInstEnv
emptyFamInstEnv = emptyUFM
famInstEnvElts :: FamInstEnv -> [FamInst]
-famInstEnvElts = concat . eltsUFM
+famInstEnvElts fi = [elt | FamIE elts _ <- eltsUFM fi, elt <- elts]
familyInstances :: (FamInstEnv, FamInstEnv) -> TyCon -> [FamInst]
familyInstances (pkg_fie, home_fie) fam
= get home_fie ++ get pkg_fie
where
get env = case lookupUFM env fam of
- Just insts -> insts
- Nothing -> []
+ Just (FamIE insts _) -> insts
+ Nothing -> []
extendFamInstEnvList :: FamInstEnv -> [FamInst] -> FamInstEnv
extendFamInstEnvList inst_env fis = foldl extendFamInstEnv inst_env fis
extendFamInstEnv :: FamInstEnv -> FamInst -> FamInstEnv
-extendFamInstEnv inst_env ins_item@(FamInst {fi_fam = cls_nm})
- = addToUFM_C add inst_env cls_nm [ins_item]
+extendFamInstEnv inst_env ins_item@(FamInst {fi_fam = cls_nm, fi_tcs = mb_tcs})
+ = addToUFM_C add inst_env cls_nm (FamIE [ins_item] ins_tyvar)
+ where
+ add (FamIE items tyvar) _ = FamIE (ins_item:items)
+ (ins_tyvar || tyvar)
+ ins_tyvar = not (any isJust mb_tcs)
+\end{code}
+
+%************************************************************************
+%* *
+ Looking up a family instance
+%* *
+%************************************************************************
+
+@lookupFamInstEnv@ looks up in a @FamInstEnv@, using a one-way match.
+Multiple matches are only possible in case of type families (not data
+families), and then, it doesn't matter which match we choose (as the
+instances are guaranteed confluent).
+
+We return the matching family instances and the type instance at which it
+matches. For example, if we lookup 'T [Int]' and have a family instance
+
+ data instance T [a] = ..
+
+desugared to
+
+ data :R42T a = ..
+ coe :Co:R42T a :: T [a] ~ :R42T a
+
+we return the matching instance '(FamInst{.., fi_tycon = :R42T}, Int)'.
+
+\begin{code}
+type FamInstMatch = (FamInst, [Type]) -- Matching type instance
+
+lookupFamInstEnv :: FamInstEnvs
+ -> TyCon -> [Type] -- What we are looking for
+ -> [FamInstMatch] -- Successful matches
+lookupFamInstEnv (pkg_ie, home_ie) fam tys
+ | not (isOpenTyCon fam)
+ = []
+ | otherwise
+ = home_matches ++ pkg_matches
where
- add items _ = ins_item:items
-\end{code}
+ rough_tcs = roughMatchTcs tys
+ all_tvs = all isNothing rough_tcs
+ home_matches = lookup home_ie
+ pkg_matches = lookup pkg_ie
+
+ --------------
+ lookup env = case lookupUFM env fam of
+ Nothing -> [] -- No instances for this class
+ Just (FamIE insts has_tv_insts)
+ -- Short cut for common case:
+ -- The thing we are looking up is of form (C a
+ -- b c), and the FamIE has no instances of
+ -- that form, so don't bother to search
+ | all_tvs && not has_tv_insts -> []
+ | otherwise -> find insts
+
+ --------------
+ find [] = []
+ find (item@(FamInst { fi_tcs = mb_tcs, fi_tvs = tpl_tvs,
+ fi_tys = tpl_tys, fi_tycon = tycon }) : rest)
+ -- Fast check for no match, uses the "rough match" fields
+ | instanceCantMatch rough_tcs mb_tcs
+ = find rest
+ -- Proper check
+ | Just subst <- tcMatchTys tpl_tvs tpl_tys tys
+ = (item, substTyVars subst (tyConTyVars tycon)) : find rest
+
+ -- No match => try next
+ | otherwise
+ = find rest
+\end{code}
+
+While @lookupFamInstEnv@ uses a one-way match, the next function
+@lookupFamInstEnvUnify@ uses two-way matching (ie, unification). This is
+needed to check for overlapping instances.
+
+For class instances, these two variants of lookup are combined into one
+function (cf, @InstEnv@). We don't do that for family instances as the
+results of matching and unification are used in two different contexts.
+Moreover, matching is the wildly more frequently used operation in the case of
+indexed synonyms and we don't want to slow that down by needless unification.
+
+\begin{code}
+lookupFamInstEnvUnify :: (FamInstEnv, FamInstEnv) -> TyCon -> [Type]
+ -> [(FamInstMatch, TvSubst)]
+lookupFamInstEnvUnify (pkg_ie, home_ie) fam tys
+ | not (isOpenTyCon fam)
+ = []
+ | otherwise
+ = home_matches ++ pkg_matches
+ where
+ rough_tcs = roughMatchTcs tys
+ all_tvs = all isNothing rough_tcs
+ home_matches = lookup home_ie
+ pkg_matches = lookup pkg_ie
+
+ --------------
+ lookup env = case lookupUFM env fam of
+ Nothing -> [] -- No instances for this class
+ Just (FamIE insts has_tv_insts)
+ -- Short cut for common case:
+ -- The thing we are looking up is of form (C a
+ -- b c), and the FamIE has no instances of
+ -- that form, so don't bother to search
+ | all_tvs && not has_tv_insts -> []
+ | otherwise -> find insts
+
+ --------------
+ find [] = []
+ find (item@(FamInst { fi_tcs = mb_tcs, fi_tvs = tpl_tvs,
+ fi_tys = tpl_tys, fi_tycon = tycon }) : rest)
+ -- Fast check for no match, uses the "rough match" fields
+ | instanceCantMatch rough_tcs mb_tcs
+ = find rest
+
+ | otherwise
+ = ASSERT2( tyVarsOfTypes tys `disjointVarSet` tpl_tvs,
+ (ppr fam <+> ppr tys <+> ppr all_tvs) $$
+ (ppr tycon <+> ppr tpl_tvs <+> ppr tpl_tys)
+ )
+ -- Unification will break badly if the variables overlap
+ -- They shouldn't because we allocate separate uniques for them
+ case tcUnifyTys bind_fn tpl_tys tys of
+ Just subst -> let rep_tys = substTyVars subst (tyConTyVars tycon)
+ in
+ ((item, rep_tys), subst) : find rest
+ Nothing -> find rest
+
+-- See explanation at @InstEnv.bind_fn@.
+--
+bind_fn tv | isTcTyVar tv && isExistentialTyVar tv = Skolem
+ | otherwise = BindMe
+\end{code}
+
+%************************************************************************
+%* *
+ Looking up a family instance
+%* *
+%************************************************************************
+
+\begin{code}
+topNormaliseType :: FamInstEnvs
+ -> Type
+ -> Maybe (Coercion, Type)
+
+-- Get rid of *outermost* (or toplevel) type functions by rewriting them
+-- By "outer" we mean that toplevelNormaliseType guarantees to return
+-- a type that does not have a reducible redex (F ty1 .. tyn) as its
+-- outermost form. It *can* return something like (Maybe (F ty)), where
+-- (F ty) is a redex.
+
+topNormaliseType env ty
+ | Just ty' <- tcView ty = topNormaliseType env ty'
+
+topNormaliseType env ty@(TyConApp tc tys)
+ | isOpenTyCon tc
+ , (ACo co, ty) <- normaliseType env ty
+ = Just (co, ty)
+
+topNormaliseType env ty
+ = Nothing
+
+
+normaliseType :: FamInstEnvs -- environment with family instances
+ -> Type -- old type
+ -> (CoercionI,Type) -- (coercion,new type), where
+ -- co :: old-type ~ new_type
+-- Normalise the input type, by eliminating all type-function redexes
+
+normaliseType env ty
+ | Just ty' <- coreView ty = normaliseType env ty'
+
+normaliseType env ty@(TyConApp tyCon tys)
+ = let -- First normalise the arg types
+ (cois, ntys) = mapAndUnzip (normaliseType env) tys
+ tycon_coi = mkTyConAppCoI tyCon ntys cois
+ in -- Now try the top-level redex
+ case lookupFamInstEnv env tyCon ntys of
+ -- A matching family instance exists
+ [(fam_inst, tys)] -> (fix_coi, nty)
+ where
+ rep_tc = famInstTyCon fam_inst
+ co_tycon = expectJust "lookupFamInst" (tyConFamilyCoercion_maybe rep_tc)
+ co = mkTyConApp co_tycon tys
+ first_coi = mkTransCoI tycon_coi (ACo co)
+ (rest_coi,nty) = normaliseType env (mkTyConApp rep_tc tys)
+ fix_coi = mkTransCoI first_coi rest_coi
+
+ -- No unique matching family instance exists;
+ -- we do not do anything
+ other -> (tycon_coi, TyConApp tyCon ntys)
+
+ where
+
+normaliseType env ty@(AppTy ty1 ty2)
+ = let (coi1,nty1) = normaliseType env ty1
+ (coi2,nty2) = normaliseType env ty2
+ in (mkAppTyCoI nty1 coi1 nty2 coi2, AppTy nty1 nty2)
+normaliseType env ty@(FunTy ty1 ty2)
+ = let (coi1,nty1) = normaliseType env ty1
+ (coi2,nty2) = normaliseType env ty2
+ in (mkFunTyCoI nty1 coi1 nty2 coi2, FunTy nty1 nty2)
+normaliseType env ty@(ForAllTy tyvar ty1)
+ = let (coi,nty1) = normaliseType env ty1
+ in (mkForAllTyCoI tyvar coi,ForAllTy tyvar nty1)
+normaliseType env ty@(NoteTy note ty1)
+ = let (coi,nty1) = normaliseType env ty1
+ in (mkNoteTyCoI note coi,NoteTy note nty1)
+normaliseType env ty@(TyVarTy _)
+ = (IdCo,ty)
+normaliseType env (PredTy predty)
+ = normalisePred env predty
+
+normalisePred :: FamInstEnvs -> PredType -> (CoercionI,Type)
+normalisePred env (ClassP cls tys)
+ = let (cois,tys') = mapAndUnzip (normaliseType env) tys
+ in (mkClassPPredCoI cls tys' cois, PredTy $ ClassP cls tys')
+normalisePred env (IParam ipn ty)
+ = let (coi,ty') = normaliseType env ty
+ in (mkIParamPredCoI ipn coi, PredTy $ IParam ipn ty')
+normalisePred env (EqPred ty1 ty2)
+ = let (coi1,ty1') = normaliseType env ty1
+ (coi2,ty2') = normaliseType env ty2
+ in (mkEqPredCoI ty1' coi1 ty2' coi2, PredTy $ EqPred ty1' ty2')
+\end{code}
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