%
+% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[InstEnv]{Utilities for typechecking instance declarations}
#include "HsVersions.h"
-import Class ( Class )
-import Var ( Id, TyVar, isTcTyVar )
+import Class
+import Var
import VarSet
-import Name ( Name, NamedThing(..), getSrcLoc, nameIsLocalOrFrom, nameModule )
-import OccName ( OccName )
-import NameSet ( unionNameSets, unitNameSet, nameSetToList )
-import Type ( TvSubst )
-import TcType ( Type, PredType, tcEqType,
- tcSplitDFunTy, tyVarsOfTypes, isExistentialTyVar,
- pprThetaArrow, pprClassPred,
- tyClsNamesOfType, tcSplitTyConApp_maybe
- )
-import TyCon ( tyConName )
-import TcGadt ( tcUnifyTys, BindFlag(..) )
-import Unify ( tcMatchTys )
+import Name
+import TcType
+import TyCon
+import TcGadt
+import Unify
import Outputable
-import BasicTypes ( OverlapFlag(..) )
-import UniqFM ( UniqFM, lookupUFM, emptyUFM, addToUFM_C, eltsUFM )
-import Id ( idType, idName )
-import SrcLoc ( pprDefnLoc )
-import Maybe ( isJust, isNothing )
+import BasicTypes
+import UniqFM
+import Id
+import SrcLoc
+
+import Data.Maybe ( isJust, isNothing )
\end{code}
data Instance
= Instance { is_cls :: Name -- Class name
- -- Used for "rough matching"; see note below
+ -- Used for "rough matching"; see Note [Rough-match field]
+ -- INVARIANT: is_tcs = roughMatchTcs is_tys
, is_tcs :: [Maybe Name] -- Top of type args
- -- Used for "proper matching"; see note
+ -- Used for "proper matching"; see Note [Proper-match fields]
, is_tvs :: TyVarSet -- Template tyvars for full match
, is_tys :: [Type] -- Full arg types
+ -- INVARIANT: is_dfun Id has type
+ -- forall is_tvs. (...) => is_cls is_tys
, is_dfun :: DFunId
, is_flag :: OverlapFlag -- See detailed comments with
-- the decl of BasicTypes.OverlapFlag
+ }
+\end{code}
+
+Note [Rough-match field]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The is_cls, is_tcs fields allow a "rough match" to be done
+without poking inside the DFunId. Poking the DFunId forces
+us to suck in all the type constructors etc it involves,
+which is a total waste of time if it has no chance of matching
+So the Name, [Maybe Name] fields allow us to say "definitely
+does not match", based only on the Name.
+
+In is_tcs,
+ Nothing means that this type arg is a type variable
+
+ (Just n) means that this type arg is a
+ TyConApp with a type constructor of n.
+ This is always a real tycon, never a synonym!
+ (Two different synonyms might match, but two
+ different real tycons can't.)
+ NB: newtypes are not transparent, though!
+
+Note [Proper-match fields]
+~~~~~~~~~~~~~~~~~~~~~~~~~
+The is_tvs, is_tys fields are simply cached values, pulled
+out (lazily) from the dfun id. They are cached here simply so
+that we don't need to decompose the DFunId each time we want
+to match it. The hope is that the fast-match fields mean
+that we often never poke th proper-match fields
- , is_orph :: Maybe OccName }
-
--- The "rough-match" fields
--- ~~~~~~~~~~~~~~~~~~~~~~~~~
--- The is_cls, is_args fields allow a "rough match" to be done
--- without poking inside the DFunId. Poking the DFunId forces
--- us to suck in all the type constructors etc it involves,
--- which is a total waste of time if it has no chance of matching
--- So the Name, [Maybe Name] fields allow us to say "definitely
--- does not match", based only on the Name.
---
--- In is_tcs,
--- Nothing means that this type arg is a type variable
---
--- (Just n) means that this type arg is a
--- TyConApp with a type constructor of n.
--- This is always a real tycon, never a synonym!
--- (Two different synonyms might match, but two
--- different real tycons can't.)
--- NB: newtypes are not transparent, though!
---
--- The "proper-match" fields
--- ~~~~~~~~~~~~~~~~~~~~~~~~~
--- The is_tvs, is_tys fields are simply cahced values, pulled
--- out (lazily) from the dfun id. They are cached here simply so
--- that we don't need to decompose the DFunId each time we want
--- to match it. The hope is that the fast-match fields mean
--- that we often never poke th proper-match fields
---
--- However, note that:
--- * is_tvs must be a superset of the free vars of is_tys
---
--- * The is_dfun must itself be quantified over exactly is_tvs
--- (This is so that we can use the matching substitution to
--- instantiate the dfun's context.)
---
--- The "orphan" field
--- ~~~~~~~~~~~~~~~~~~
--- An instance is an orphan if its head (after the =>) mentions
--- nothing defined in this module.
---
--- Just n The head mentions n, which is defined in this module
--- This is used for versioning; the instance decl is
--- considered part of the defn of n when computing versions
---
--- Nothing The head mentions nothing defined in this module
---
--- If a module contains any orphans, then its interface file is read
--- regardless, so that its instances are not missed.
---
--- Functional dependencies worsen the situation a bit. Consider
--- class C a b | a -> b
--- In some other module we might have
--- module M where
--- data T = ...
--- instance C Int T where ...
--- This isn't considered an orphan, so we will only read M's interface
--- if something from M is used (e.g. T). So there's a risk we'll
--- miss the improvement from the instance. Workaround: import M.
+However, note that:
+ * is_tvs must be a superset of the free vars of is_tys
+ * The is_dfun must itself be quantified over exactly is_tvs
+ (This is so that we can use the matching substitution to
+ instantiate the dfun's context.)
+
+
+
+\begin{code}
instanceDFunId :: Instance -> DFunId
instanceDFunId = is_dfun
mkLocalInstance dfun oflag
= Instance { is_flag = oflag, is_dfun = dfun,
is_tvs = mkVarSet tvs, is_tys = tys,
- is_cls = cls_name, is_tcs = roughMatchTcs tys,
- is_orph = orph }
+ is_cls = className cls, is_tcs = roughMatchTcs tys }
where
(tvs, _, cls, tys) = tcSplitDFunTy (idType dfun)
- mod = nameModule (idName dfun)
- cls_name = getName cls
- tycl_names = foldr (unionNameSets . tyClsNamesOfType)
- (unitNameSet cls_name) tys
- orph = case filter (nameIsLocalOrFrom mod) (nameSetToList tycl_names) of
- [] -> Nothing
- (n:ns) -> Just (getOccName n)
-
-mkImportedInstance :: Name -> [Maybe Name] -> Maybe OccName
+
+mkImportedInstance :: Name -> [Maybe Name]
-> DFunId -> OverlapFlag -> Instance
-- Used for imported instances, where we get the rough-match stuff
-- from the interface file
-mkImportedInstance cls mb_tcs orph dfun oflag
+mkImportedInstance cls mb_tcs dfun oflag
= Instance { is_flag = oflag, is_dfun = dfun,
is_tvs = mkVarSet tvs, is_tys = tys,
- is_cls = cls, is_tcs = mb_tcs, is_orph = orph }
+ is_cls = cls, is_tcs = mb_tcs }
where
(tvs, _, _, tys) = tcSplitDFunTy (idType dfun)
= find ms us rest
| otherwise
- = ASSERT2( not (tyVarsOfTypes tys `intersectsVarSet` tpl_tvs),
- (ppr cls <+> ppr tys <+> ppr all_tvs) $$
- (ppr dfun <+> ppr tpl_tvs <+> ppr tpl_tys)
+ = ASSERT2( tyVarsOfTypes tys `disjointVarSet` tpl_tvs,
+ (ppr cls <+> ppr tys <+> ppr all_tvs) $$
+ (ppr dfun <+> ppr tpl_tvs <+> ppr tpl_tys)
)
-- Unification will break badly if the variables overlap
-- They shouldn't because we allocate separate uniques for them
projects / ghc-hetmet.git / blobdiff