\begin{code}
module InstEnv (
- DFunId, ClsInstEnv, InstEnv,
+ DFunId, InstEnv,
- emptyInstEnv, extendInstEnv, pprInstEnv,
- lookupInstEnv, InstLookupResult(..),
- classInstEnv, simpleDFunClassTyCon
+ emptyInstEnv, extendInstEnv,
+ lookupInstEnv, instEnvElts,
+ classInstances, simpleDFunClassTyCon, checkFunDeps
) where
#include "HsVersions.h"
import Class ( Class, classTvsFds )
-import Var ( TyVar, Id )
+import Var ( Id, isTcTyVar )
import VarSet
import VarEnv
-import Maybes ( MaybeErr(..), returnMaB, failMaB, thenMaB, maybeToBool )
-import Name ( getSrcLoc )
-import TcType ( Type, tcTyConAppTyCon, mkTyVarTy,
- tcSplitDFunTy, tyVarsOfTypes,
- matchTys, unifyTyListsX, allDistinctTyVars
+import TcType ( Type, tcTyConAppTyCon, tcIsTyVarTy,
+ tcSplitDFunTy, tyVarsOfTypes, isExistentialTyVar,
+ matchTys, unifyTyListsX
)
-import PprType ( pprClassPred )
import FunDeps ( checkClsFD )
import TyCon ( TyCon )
import Outputable
-import UniqFM ( UniqFM, lookupWithDefaultUFM, addToUFM, emptyUFM, eltsUFM )
+import UniqFM ( UniqFM, lookupUFM, emptyUFM, addToUFM_C, eltsUFM )
import Id ( idType )
-import ErrUtils ( Message )
import CmdLineOpts
+import Util ( notNull )
+import Maybe ( isJust )
\end{code}
\begin{code}
type DFunId = Id
+type InstEnv = UniqFM ClsInstEnv -- Maps Class to instances for that class
+
+data ClsInstEnv
+ = ClsIE [InstEnvElt] -- The instances for a particular class, in any order
+ Bool -- True <=> there is an instance of form C a b c
+ -- If *not* then the common case of looking up
+ -- (C a b c) can fail immediately
+ -- NB: use tcIsTyVarTy: don't look through newtypes!!
+
+type InstEnvElt = (TyVarSet, [Type], DFunId)
+ -- INVARIANTs: see notes below
-type InstEnv = UniqFM ClsInstEnv -- Maps Class to instances for that class
+emptyInstEnv :: InstEnv
+emptyInstEnv = emptyUFM
-simpleDFunClassTyCon :: DFunId -> (Class, TyCon)
-simpleDFunClassTyCon dfun
- = (clas, tycon)
+instEnvElts :: InstEnv -> [InstEnvElt]
+instEnvElts ie = [elt | ClsIE elts _ <- eltsUFM ie, elt <- elts]
+
+classInstances :: (InstEnv,InstEnv) -> Class -> [InstEnvElt]
+classInstances (pkg_ie, home_ie) cls
+ = get home_ie ++ get pkg_ie
where
- (_,_,clas,[ty]) = tcSplitDFunTy (idType dfun)
- tycon = tcTyConAppTyCon ty
+ get env = case lookupUFM env cls of
+ Just (ClsIE insts _) -> insts
+ Nothing -> []
+
+extendInstEnv :: InstEnv -> DFunId -> InstEnv
+extendInstEnv inst_env dfun_id
+ = addToUFM_C add inst_env clas (ClsIE [ins_item] ins_tyvar)
+ where
+ add (ClsIE cur_insts cur_tyvar) _ = ClsIE (ins_item : cur_insts)
+ (ins_tyvar || cur_tyvar)
+ (ins_tvs, _, clas, ins_tys) = tcSplitDFunTy (idType dfun_id)
+ ins_tv_set = mkVarSet ins_tvs
+ ins_item = (ins_tv_set, ins_tys, dfun_id)
+ ins_tyvar = all tcIsTyVarTy ins_tys
+#ifdef UNUSED
pprInstEnv :: InstEnv -> SDoc
pprInstEnv env
= vcat [ brackets (pprWithCommas ppr (varSetElems tyvars)) <+>
brackets (pprWithCommas ppr tys) <+> ppr dfun
- | cls_inst_env <- eltsUFM env
+ | ClsIE cls_inst_env _ <- eltsUFM env
, (tyvars, tys, dfun) <- cls_inst_env
]
+#endif
+
+simpleDFunClassTyCon :: DFunId -> (Class, TyCon)
+simpleDFunClassTyCon dfun
+ = (clas, tycon)
+ where
+ (_,_,clas,[ty]) = tcSplitDFunTy (idType dfun)
+ tycon = tcTyConAppTyCon ty
\end{code}
%************************************************************************
%* *
%************************************************************************
-\begin{code}
-type ClsInstEnv = [(TyVarSet, [Type], DFunId)] -- The instances for a particular class
- -- INVARIANTs: see notes below
-
-emptyInstEnv :: InstEnv
-emptyInstEnv = emptyUFM
-
-classInstEnv :: InstEnv -> Class -> ClsInstEnv
-classInstEnv env cls = lookupWithDefaultUFM env [] cls
-\end{code}
-
A @ClsInstEnv@ all the instances of that class. The @Id@ inside a
ClsInstEnv mapping is the dfun for that instance.
thing we are looking up can have an arbitrary "flexi" part.
\begin{code}
-lookupInstEnv :: InstEnv -- The envt
- -> Class -> [Type] -- Key
- -> InstLookupResult
-
-data InstLookupResult
- = FoundInst -- There is a (template,substitution) pair
- -- that makes the template match the key,
- -- and no template is an instance of the key
- TyVarSubstEnv Id
-
- | NoMatch Bool -- Boolean is true iff there is at least one
- -- template that matches the key.
- -- (but there are other template(s) that are
- -- instances of the key, so we don't report
- -- FoundInst)
- -- The NoMatch True case happens when we look up
+lookupInstEnv :: DynFlags
+ -> (InstEnv -- External package inst-env
+ ,InstEnv) -- Home-package inst-env
+ -> Class -> [Type] -- What we are looking for
+ -> ([(TyVarSubstEnv, InstEnvElt)], -- Successful matches
+ [Id]) -- These don't match but do unify
+ -- The second component of the tuple happens when we look up
-- Foo [a]
-- in an InstEnv that has entries for
-- Foo [Int]
-- Foo [b]
-- Then which we choose would depend on the way in which 'a'
- -- is instantiated. So we say there is no match, but identify
- -- it as ambiguous case in the hope of giving a better error msg.
- -- See the notes above from Jeff Lewis
-
-lookupInstEnv env key_cls key_tys
- = find (classInstEnv env key_cls)
+ -- is instantiated. So we report that Foo [b] is a match (mapping b->a)
+ -- but Foo [Int] is a unifier. This gives the caller a better chance of
+ -- giving a suitable error messagen
+
+lookupInstEnv dflags (pkg_ie, home_ie) cls tys
+ | not (null all_unifs) = (all_matches, all_unifs) -- This is always an error situation,
+ -- so don't attempt to pune the matches
+ | otherwise = (pruned_matches, [])
where
- key_vars = tyVarsOfTypes key_tys
-
- find [] = NoMatch False
- find ((tpl_tyvars, tpl, dfun_id) : rest)
+ all_tvs = all tcIsTyVarTy tys
+ incoherent_ok = dopt Opt_AllowIncoherentInstances dflags
+ overlap_ok = dopt Opt_AllowOverlappingInstances dflags
+ (home_matches, home_unifs) = lookup_inst_env home_ie cls tys all_tvs
+ (pkg_matches, pkg_unifs) = lookup_inst_env pkg_ie cls tys all_tvs
+ all_matches = home_matches ++ pkg_matches
+ all_unifs | incoherent_ok = [] -- Don't worry about these if incoherent is ok!
+ | otherwise = home_unifs ++ pkg_unifs
+
+ pruned_matches | overlap_ok = foldr insert_overlapping [] all_matches
+ | otherwise = all_matches
+
+lookup_inst_env :: InstEnv -- The envt
+ -> Class -> [Type] -- What we are looking for
+ -> Bool -- All the [Type] are tyvars
+ -> ([(TyVarSubstEnv, InstEnvElt)], -- Successful matches
+ [Id]) -- These don't match but do unify
+lookup_inst_env env key_cls key_tys key_all_tvs
+ = case lookupUFM env key_cls of
+ Nothing -> ([],[]) -- No instances for this class
+ Just (ClsIE insts has_tv_insts)
+ | key_all_tvs && not has_tv_insts -> ([],[]) -- Short cut for common case
+ -- The thing we are looking up is of form (C a b c), and
+ -- the ClsIE has no instances of that form, so don't bother to search
+ | otherwise -> find insts [] []
+ where
+ key_vars = filterVarSet not_existential (tyVarsOfTypes key_tys)
+ not_existential tv = not (isTcTyVar tv && isExistentialTyVar tv)
+ -- The key_tys can contain skolem constants, and we can guarantee that those
+ -- are never going to be instantiated to anything, so we should not involve
+ -- them in the unification test. Example:
+ -- class Foo a where { op :: a -> Int }
+ -- instance Foo a => Foo [a] -- NB overlap
+ -- instance Foo [Int] -- NB overlap
+ -- data T = forall a. Foo a => MkT a
+ -- f :: T -> Int
+ -- f (MkT x) = op [x,x]
+ -- The op [x,x] means we need (Foo [a]). Without the filterVarSet we'd
+ -- complain, saying that the choice of instance depended on the instantiation
+ -- of 'a'; but of course it isn't *going* to be instantiated.
+
+ find [] ms us = (ms, us)
+ find (item@(tpl_tyvars, tpl, dfun_id) : rest) ms us
= case matchTys tpl_tyvars tpl key_tys of
- Nothing ->
- -- Check whether the things unify, so that
- -- we bale out if a later instantiation of this
- -- predicate might match this instance
- -- [see notes about overlapping instances above]
- case unifyTyListsX (key_vars `unionVarSet` tpl_tyvars) key_tys tpl of
- Nothing -> find rest
- Just _ -> NoMatch (any_match rest)
Just (subst, leftovers) -> ASSERT( null leftovers )
- FoundInst subst dfun_id
+ find rest ((subst,item):ms) us
+ Nothing
+ -- Does not match, so next check whether the things unify
+ -- [see notes about overlapping instances above]
+ -> ASSERT( not (key_vars `intersectsVarSet` tpl_tyvars) )
+ -- Unification will break badly if the variables overlap
+ -- They shouldn't because we allocate separate uniques for them
+ case unifyTyListsX (key_vars `unionVarSet` tpl_tyvars) key_tys tpl of
+ Just _ -> find rest ms (dfun_id:us)
+ Nothing -> find rest ms us
+
+insert_overlapping :: (TyVarSubstEnv, InstEnvElt) -> [(TyVarSubstEnv, InstEnvElt)]
+ -> [(TyVarSubstEnv, InstEnvElt)]
+-- Add a new solution, knocking out strictly less specific ones
+insert_overlapping new_item [] = [new_item]
+insert_overlapping new_item (item:items)
+ | new_beats_old && old_beats_new = item : insert_overlapping new_item items
+ -- Duplicate => keep both for error report
+ | new_beats_old = insert_overlapping new_item items
+ -- Keep new one
+ | old_beats_new = item : items
+ -- Keep old one
+ | otherwise = item : insert_overlapping new_item items
+ -- Keep both
+ where
+ new_beats_old = new_item `beats` item
+ old_beats_new = item `beats` new_item
- any_match rest = or [ maybeToBool (matchTys tvs tpl key_tys)
- | (tvs,tpl,_) <- rest
- ]
+ (_, (tvs1, tys1, _)) `beats` (_, (tvs2, tys2, _))
+ = isJust (matchTys tvs2 tys2 tys1) -- A beats B if A is more specific than B
+ -- I.e. if B can be instantiated to match A
\end{code}
%************************************************************************
%* *
-\subsection{Extending an instance environment}
+ Functional dependencies
%* *
%************************************************************************
-@extendInstEnv@ extends a @ClsInstEnv@, checking for overlaps.
-
-A boolean flag controls overlap reporting.
-
-True => overlap is permitted, but only if one template matches the other;
- not if they unify but neither is
-
-\begin{code}
-extendInstEnv :: DynFlags -> InstEnv -> [DFunId] -> (InstEnv, [Message])
- -- Similar, but all we have is the DFuns
-extendInstEnv dflags env dfun_ids = foldl (addToInstEnv dflags) (env, []) dfun_ids
-
-
-addToInstEnv :: DynFlags
- -> (InstEnv, [Message])
- -> DFunId
- -> (InstEnv, [Message]) -- Resulting InstEnv and augmented error messages
-
-addToInstEnv dflags (inst_env, errs) dfun_id
- -- Check first that the new instance doesn't
- -- conflict with another. See notes below about fundeps.
- | not (null bad_fundeps)
- = (inst_env, fundep_err : errs) -- Bad fundeps; report the first only
-
- | otherwise
- = case insert_into cls_inst_env of
- Failed err -> (inst_env, err : errs)
- Succeeded new_env -> (addToUFM inst_env clas new_env, errs)
-
- where
- cls_inst_env = classInstEnv inst_env clas
- (ins_tvs, _, clas, ins_tys) = tcSplitDFunTy (idType dfun_id)
- bad_fundeps = badFunDeps cls_inst_env clas ins_tv_set ins_tys
- fundep_err = fundepErr dfun_id (head bad_fundeps)
-
- ins_tv_set = mkVarSet ins_tvs
- ins_item = (ins_tv_set, ins_tys, dfun_id)
-
- insert_into [] = returnMaB [ins_item]
- insert_into env@(cur_item@(tpl_tvs, tpl_tys, tpl_dfun_id) : rest)
- = case unifyTyListsX (ins_tv_set `unionVarSet` tpl_tvs) tpl_tys ins_tys of
- Just subst -> insert_unifiable env subst
- Nothing -> carry_on cur_item rest
-
- carry_on cur_item rest = insert_into rest `thenMaB` \ rest' ->
- returnMaB (cur_item : rest')
-
- -- The two templates unify. This is acceptable iff
- -- (a) -fallow-overlapping-instances is on
- -- (b) one is strictly more specific than the other
- -- [It's bad if they are identical or incomparable]
- insert_unifiable env@(cur_item@(tpl_tvs, tpl_tys, tpl_dfun_id) : rest) subst
- | ins_item_more_specific && cur_item_more_specific
- = -- Duplicates
- failMaB (dupInstErr dfun_id tpl_dfun_id)
-
- | not (dopt Opt_AllowOverlappingInstances dflags)
- || not (ins_item_more_specific || cur_item_more_specific)
- = -- Overlap illegal, or the two are incomparable
- failMaB (overlapErr dfun_id tpl_dfun_id)
-
- | otherwise
- = -- OK, it's acceptable. Remaining question is whether
- -- we drop it here or compare it with others
- if ins_item_more_specific then
- -- New item is an instance of current item, so drop it here
- returnMaB (ins_item : env)
- else
- carry_on cur_item rest
-
- where
- ins_item_more_specific = allVars subst ins_tvs
- cur_item_more_specific = allVars subst (varSetElems tpl_tvs)
-
-allVars :: TyVarSubstEnv -> [TyVar] -> Bool
--- True iff all the type vars are mapped to distinct type vars
-allVars subst tvs
- = allDistinctTyVars (map lookup tvs) emptyVarSet
- where
- lookup tv = case lookupSubstEnv subst tv of
- Just (DoneTy ty) -> ty
- Nothing -> mkTyVarTy tv
-\end{code}
-
-Functional dependencies
-~~~~~~~~~~~~~~~~~~~~~~~
Here is the bad case:
class C a b | a->b where ...
instance C Int Bool where ...
if s1 matches
-
-
\begin{code}
-badFunDeps :: ClsInstEnv -> Class
+checkFunDeps :: (InstEnv, InstEnv) -> DFunId
+ -> Maybe [DFunId] -- Nothing <=> ok
+ -- Just dfs <=> conflict with dfs
+-- Check wheher adding DFunId would break functional-dependency constraints
+checkFunDeps inst_envs dfun
+ | null bad_fundeps = Nothing
+ | otherwise = Just bad_fundeps
+ where
+ (ins_tvs, _, clas, ins_tys) = tcSplitDFunTy (idType dfun)
+ ins_tv_set = mkVarSet ins_tvs
+ cls_inst_env = classInstances inst_envs clas
+ bad_fundeps = badFunDeps cls_inst_env clas ins_tv_set ins_tys
+
+badFunDeps :: [InstEnvElt] -> Class
-> TyVarSet -> [Type] -- Proposed new instance type
-> [DFunId]
badFunDeps cls_inst_env clas ins_tv_set ins_tys
= [ dfun_id | fd <- fds,
(tvs, tys, dfun_id) <- cls_inst_env,
- not (null (checkClsFD (tvs `unionVarSet` ins_tv_set) fd clas_tvs tys ins_tys))
+ notNull (checkClsFD (tvs `unionVarSet` ins_tv_set) fd clas_tvs tys ins_tys)
]
where
(clas_tvs, fds) = classTvsFds clas
\end{code}
-
-
-\begin{code}
-dupInstErr dfun1 dfun2 = addInstErr (ptext SLIT("Duplicate instance declarations:")) dfun1 dfun2
-overlapErr dfun1 dfun2 = addInstErr (ptext SLIT("Overlapping instance declarations:")) dfun1 dfun2
-fundepErr dfun1 dfun2 = addInstErr (ptext SLIT("Functional dependencies conflict between instance declarations:"))
- dfun1 dfun2
-
-addInstErr what dfun1 dfun2
- = hang what 2 (ppr_dfun dfun1 $$ ppr_dfun dfun2)
- where
- ppr_dfun dfun = ppr (getSrcLoc dfun) <> colon <+> pprClassPred clas tys
- where
- (_,_,clas,tys) = tcSplitDFunTy (idType dfun)
-\end{code}
projects / ghc-hetmet.git / blobdiff