\begin{code}
module InstEnv (
- DFunId, ClsInstEnv, InstEnv,
+ DFunId, InstEnv,
- emptyInstEnv, extendInstEnv, pprInstEnv,
- lookupInstEnv, InstLookupResult(..),
- classInstEnv, simpleDFunClassTyCon
+ emptyInstEnv, extendInstEnv,
+ lookupInstEnv,
+ classInstEnv, simpleDFunClassTyCon, checkFunDeps
) where
#include "HsVersions.h"
-import Class ( Class )
+import Class ( Class, classTvsFds )
import Var ( Id )
-import VarSet ( TyVarSet, unionVarSet, mkVarSet, varSetElems )
-import VarEnv ( TyVarSubstEnv )
-import Maybes ( MaybeErr(..), returnMaB, failMaB, thenMaB, maybeToBool )
-import Name ( getSrcLoc )
-import Type ( Type, tyConAppTyCon,
- splitSigmaTy, splitDFunTy, tyVarsOfTypes
+import VarSet
+import VarEnv
+import TcType ( Type, tcTyConAppTyCon,
+ tcSplitDFunTy, tyVarsOfTypes,
+ matchTys, unifyTyListsX
)
-import PprType ( )
+import FunDeps ( checkClsFD )
import TyCon ( TyCon )
import Outputable
-import Unify ( matchTys, unifyTyListsX )
-import UniqFM ( UniqFM, lookupWithDefaultUFM, addToUFM, emptyUFM, eltsUFM )
+import UniqFM ( UniqFM, lookupWithDefaultUFM, emptyUFM, eltsUFM, addToUFM_C )
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
+type ClsInstEnv = [InstEnvElt] -- The instances for a particular class
+type InstEnvElt = (TyVarSet, [Type], DFunId)
+ -- INVARIANTs: see notes below
-type InstEnv = UniqFM ClsInstEnv -- Maps Class to instances for that class
+emptyInstEnv :: InstEnv
+emptyInstEnv = emptyUFM
-type ClsInstEnv = [(TyVarSet, [Type], DFunId)] -- The instances for a particular class
+classInstEnv :: InstEnv -> Class -> ClsInstEnv
+classInstEnv env cls = lookupWithDefaultUFM env [] cls
-simpleDFunClassTyCon :: DFunId -> (Class, TyCon)
-simpleDFunClassTyCon dfun
- = (clas, tycon)
+extendInstEnv :: InstEnv -> DFunId -> InstEnv
+extendInstEnv inst_env dfun_id
+ = addToUFM_C add inst_env clas [ins_item]
where
- (_,_,clas,[ty]) = splitDFunTy (idType dfun)
- tycon = tyConAppTyCon ty
+ add old _ = ins_item : old
+ (ins_tvs, _, clas, ins_tys) = tcSplitDFunTy (idType dfun_id)
+ ins_tv_set = mkVarSet ins_tvs
+ ins_item = (ins_tv_set, ins_tys, dfun_id)
+#ifdef UNUSED
pprInstEnv :: InstEnv -> SDoc
pprInstEnv env
= vcat [ brackets (pprWithCommas ppr (varSetElems tyvars)) <+>
| 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}
%************************************************************************
%* *
%************************************************************************
-The actual type declarations are in HscTypes.
-
-\begin{code}
-emptyInstEnv :: InstEnv
-emptyInstEnv = emptyUFM
-
-classInstEnv :: InstEnv -> Class -> ClsInstEnv
-classInstEnv env cls = lookupWithDefaultUFM env [] cls
-\end{code}
-
-A @ClsInstEnv@ lives inside a class, and identifies all the instances
-of that class. The @Id@ inside a ClsInstEnv mapping is the dfun for
-that instance.
+A @ClsInstEnv@ all the instances of that class. The @Id@ inside a
+ClsInstEnv mapping is the dfun for that instance.
If class C maps to a list containing the item ([a,b], [t1,t2,t3], dfun), then
* [a,b] must be a superset of the free vars of [t1,t2,t3]
* The dfun must itself be quantified over [a,b]
+
+ * More specific instances come before less specific ones,
+ where they overlap
Thus, the @ClassInstEnv@ for @Eq@ might contain the following entry:
[a] ===> dfun_Eq_List :: forall a. Eq a => Eq [a]
--Jeff
+BUT NOTE [Nov 2001]: we must actually *unify* not reverse-match in
+this test. Suppose the instance envt had
+ ..., forall a b. C a a b, ..., forall a b c. C a b c, ...
+(still most specific first)
+Now suppose we are looking for (C x y Int), where x and y are unconstrained.
+ C x y Int doesn't match the template {a,b} C a a b
+but neither does
+ C a a b match the template {x,y} C x y Int
+But still x and y might subsequently be unified so they *do* match.
+
+Simple story: unify, don't match.
+
+
+%************************************************************************
+%* *
+\subsection{Looking up an instance}
+%* *
+%************************************************************************
@lookupInstEnv@ looks up in a @InstEnv@, using a one-way match. Since
the env is kept ordered, the first match must be the only one. The
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
+ incoherent_ok = dopt Opt_AllowIncoherentInstances dflags
+ overlap_ok = dopt Opt_AllowOverlappingInstances dflags
+ (home_matches, home_unifs) = lookup_inst_env home_ie cls tys
+ (pkg_matches, pkg_unifs) = lookup_inst_env pkg_ie cls tys
+ 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
+ -> ([(TyVarSubstEnv, InstEnvElt)], -- Successful matches
+ [Id]) -- These don't match but do unify
+lookup_inst_env env key_cls key_tys
+ = find (classInstEnv env key_cls) [] []
where
key_vars = tyVarsOfTypes key_tys
- find [] = NoMatch False
- find ((tpl_tyvars, tpl, val) : rest)
+ find [] ms us = (ms, us)
+ find (item@(tpl_tyvars, tpl, dfun_id) : rest) ms us
= case matchTys tpl_tyvars tpl key_tys of
- Nothing ->
- case matchTys key_vars key_tys tpl of
- Nothing -> find rest
- Just (_, _) -> NoMatch (any_match rest)
Just (subst, leftovers) -> ASSERT( null leftovers )
- FoundInst subst val
+ find rest ((subst,item):ms) us
+ Nothing
+ -- Does not match, so next check whether the things unify
+ -- [see notes about overlapping instances above]
+ -> 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}
-@addToClsInstEnv@ extends a @ClsInstEnv@, checking for overlaps.
-A boolean flag controls overlap reporting.
+%************************************************************************
+%* *
+ Functional dependencies
+%* *
+%************************************************************************
+
+Here is the bad case:
+ class C a b | a->b where ...
+ instance C Int Bool where ...
+ instance C Int Char where ...
+
+The point is that a->b, so Int in the first parameter must uniquely
+determine the second. In general, given the same class decl, and given
+
+ instance C s1 s2 where ...
+ instance C t1 t2 where ...
+
+Then the criterion is: if U=unify(s1,t1) then U(s2) = U(t2).
+
+Matters are a little more complicated if there are free variables in
+the s2/t2.
+
+ class D a b c | a -> b
+ instance D a b => D [(a,a)] [b] Int
+ instance D a b => D [a] [b] Bool
+
+The instance decls don't overlap, because the third parameter keeps
+them separate. But we want to make sure that given any constraint
+ D s1 s2 s3
+if s1 matches
-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 infos
- = go env [] infos
- where
- go env msgs [] = (env, msgs)
- go env msgs (dfun:dfuns) = case addToInstEnv dflags env dfun of
- Succeeded new_env -> go new_env msgs dfuns
- Failed dfun' -> go env (msg:msgs) dfuns
- where
- msg = dupInstErr dfun dfun'
-
-
-dupInstErr dfun1 dfun2
- -- Overlapping/duplicate instances for given class; msg could be more glamourous
- = hang (ptext SLIT("Duplicate or overlapping instance declarations:"))
- 2 (ppr_dfun dfun1 $$ ppr_dfun dfun2)
+checkFunDeps :: (InstEnv, InstEnv) -> DFunId
+ -> Maybe [DFunId] -- Nothing <=> ok
+ -- Just dfs <=> conflict with dfs
+-- Check wheher adding DFunId would break functional-dependency constraints
+checkFunDeps (pkg_ie, home_ie) dfun
+ | null bad_fundeps = Nothing
+ | otherwise = Just bad_fundeps
where
- ppr_dfun dfun = ppr (getSrcLoc dfun) <> colon <+> ppr tau
- where
- (_,_,tau) = splitSigmaTy (idType dfun)
-
-addToInstEnv :: DynFlags
- -> InstEnv -> DFunId
- -> MaybeErr InstEnv -- Success...
- DFunId -- Failure: Offending overlap
-
-addToInstEnv dflags inst_env dfun_id
- = case insert_into (classInstEnv inst_env clas) of
- Failed stuff -> Failed stuff
- Succeeded new_env -> Succeeded (addToUFM inst_env clas new_env)
-
+ (ins_tvs, _, clas, ins_tys) = tcSplitDFunTy (idType dfun)
+ ins_tv_set = mkVarSet ins_tvs
+ cls_inst_env = classInstEnv home_ie clas ++ classInstEnv pkg_ie clas
+ bad_fundeps = badFunDeps cls_inst_env clas ins_tv_set ins_tys
+
+badFunDeps :: ClsInstEnv -> 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,
+ notNull (checkClsFD (tvs `unionVarSet` ins_tv_set) fd clas_tvs tys ins_tys)
+ ]
where
- (ins_tvs, _, clas, ins_tys) = splitDFunTy (idType dfun_id)
-
- 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, val) : rest)
-
- -- FAIL if:
- -- (a) they are the same, or
- -- (b) they unify, and any sort of overlap is prohibited,
- -- (c) they unify but neither is more specific than t'other
- | identical
- || (unifiable && not (dopt Opt_AllowOverlappingInstances dflags))
- || (unifiable && not (ins_item_more_specific || cur_item_more_specific))
- = failMaB val
-
- -- New item is an instance of current item, so drop it here
- | ins_item_more_specific = returnMaB (ins_item : env)
-
- -- Otherwise carry on
- | otherwise = insert_into rest `thenMaB` \ rest' ->
- returnMaB (cur_item : rest')
- where
- unifiable = maybeToBool (unifyTyListsX (ins_tv_set `unionVarSet` tpl_tvs) tpl_tys ins_tys)
- ins_item_more_specific = maybeToBool (matchTys tpl_tvs tpl_tys ins_tys)
- cur_item_more_specific = maybeToBool (matchTys ins_tv_set ins_tys tpl_tys)
- identical = ins_item_more_specific && cur_item_more_specific
+ (clas_tvs, fds) = classTvsFds clas
\end{code}
-
-
projects / ghc-hetmet.git / blobdiff