2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1999
4 \section[Variance]{Variance in @Type@ and @TyCon@}
12 #include "HsVersions.h"
14 import TypeRep ( Type(..), TyNote(..) ) -- friend
15 import TyCon ( TyCon, ArgVrcs, tyConArity, tyConDataCons_maybe, tyConDataCons, tyConTyVars,
16 tyConArgVrcs_maybe, getSynTyConDefn, isSynTyCon, isAlgTyCon )
17 import DataCon ( dataConRepArgTys )
22 import Maybes ( expectJust )
23 import Maybe ( isNothing )
28 Computing the tyConArgVrcs info
29 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
31 @tyConArgVrcs@ gives a list of (occPos,occNeg) flags, one for each
32 tyvar. For @AlgTyCon@s and @SynTyCon@s, this info must be precomputed
33 separately. Note that this is information about occurrences of type
34 variables, not usages of term variables.
36 The function @calcTyConArgVrcs@ must be passed a list of *algebraic or
37 syntycons only* such that all tycons referred to (by mutual recursion)
38 appear in the list. The fixpointing will be done on this set of
39 tycons as a whole. It returns a list of @tyconVrcInfo@ data, ready to
40 be (knot-tyingly?) stuck back into the appropriate fields.
43 calcTyConArgVrcs :: [TyCon] -> FiniteMap TyCon ArgVrcs
45 calcTyConArgVrcs tycons
49 initial_oi :: FiniteMap TyCon ArgVrcs
50 initial_oi = foldl (\fm tc -> addToFM fm tc (initial tc)) emptyFM tycons
51 initial tc = if isAlgTyCon tc && isNothing (tyConDataCons_maybe tc) then
52 -- make pessimistic assumption (and warn)
55 replicate (tyConArity tc) (False,False)
57 tcaoFix :: FiniteMap TyCon ArgVrcs -- initial ArgVrcs per tycon
58 -> FiniteMap TyCon ArgVrcs -- fixpointed ArgVrcs per tycon
60 tcaoFix oi = let (changed,oi') = foldFM (\ tc pms
62 -> let pms' = tcaoIter oi' tc -- seq not simult
63 in (changed || (pms /= pms'),
65 (False,oi) -- seq not simult for faster fixpting
71 tcaoIter :: FiniteMap TyCon ArgVrcs -- reference ArgVrcs (initial)
72 -> TyCon -- tycon to update
73 -> ArgVrcs -- new ArgVrcs for tycon
75 tcaoIter oi tc | isAlgTyCon tc
76 = if null data_cons then
77 -- Abstract types get uninformative variances
80 map (\v -> anyVrc (\ty -> vrcInTy myfao v ty) argtys)
83 data_cons = tyConDataCons tc
85 argtys = concatMap dataConRepArgTys data_cons
86 myfao tc = lookupWithDefaultFM oi (expectJust "tcaoIter(Alg)" $
87 tyConArgVrcs_maybe tc)
89 -- we use the already-computed result for tycons not in this SCC
91 tcaoIter oi tc | isSynTyCon tc
92 = let (tyvs,ty) = getSynTyConDefn tc
93 myfao tc = lookupWithDefaultFM oi (expectJust "tcaoIter(Syn)" $
94 tyConArgVrcs_maybe tc)
96 -- we use the already-computed result for tycons not in this SCC
97 in map (\v -> vrcInTy myfao v ty) tyvs
100 abstractVrcs :: TyCon -> ArgVrcs
103 pprTrace "Vrc: abstract tycon:" (ppr tc) $
105 replicate (tyConArity tc) (True,True)
109 Variance of tyvars in a type
110 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
112 A general variance-check function. We pass a function for determining
113 the @ArgVrc@s of a tycon; when fixpointing this refers to the current
114 value; otherwise this should be looked up from the tycon's own
118 vrcInTy :: (TyCon -> ArgVrcs) -- function to get argVrcs of a tycon (break out of recursion)
119 -> TyVar -- tyvar to check Vrcs of
120 -> Type -- type to check for occ in
121 -> (Bool,Bool) -- (occurs positively, occurs negatively)
123 vrcInTy fao v (NoteTy (SynNote _) ty) = vrcInTy fao v ty
124 -- SynTyCon doesn't neccessarily have vrcInfo at this point,
125 -- so don't try and use it
127 vrcInTy fao v (NoteTy (FTVNote ftv) ty) = if elemVarSet v ftv
128 then vrcInTy fao v ty
130 -- note that ftv cannot be calculated as occPos||occNeg,
131 -- since if a tyvar occurs only as unused tyconarg,
132 -- occPos==occNeg==False, but ftv=True
134 vrcInTy fao v (TyVarTy v') = if v==v'
138 vrcInTy fao v (AppTy ty1 ty2) = if vrcInTy fao v ty2 /= (False,False)
140 else vrcInTy fao v ty1
141 -- ty1 is probably unknown (or it would have been beta-reduced);
142 -- hence if v occurs in ty2 at all then it could occur with
143 -- either variance. Otherwise it occurs as it does in ty1.
145 vrcInTy fao v (FunTy ty1 ty2) = negVrc (vrcInTy fao v ty1)
149 vrcInTy fao v (ForAllTy v' ty) = if v==v'
151 else vrcInTy fao v ty
153 vrcInTy fao v (TyConApp tc tys) = let pms1 = map (vrcInTy fao v) tys
155 in orVrcs (zipWith timesVrc pms1 pms2)
159 External entry point: assumes tyconargvrcs already computed.
162 tyVarVrc :: TyVar -- tyvar to check Vrc of
163 -> Type -- type to check for occ in
164 -> (Bool,Bool) -- (occurs positively, occurs negatively)
166 tyVarVrc = vrcInTy (expectJust "tyVarVrcs" . tyConArgVrcs_maybe)
174 orVrc :: (Bool,Bool) -> (Bool,Bool) -> (Bool,Bool)
175 orVrc (p1,m1) (p2,m2) = (p1||p2,m1||m2)
177 orVrcs :: [(Bool,Bool)] -> (Bool,Bool)
178 orVrcs = foldl orVrc (False,False)
180 negVrc :: (Bool,Bool) -> (Bool,Bool)
181 negVrc (p1,m1) = (m1,p1)
183 anyVrc :: (a -> (Bool,Bool)) -> [a] -> (Bool,Bool)
184 anyVrc p as = foldl (\ pm a -> pm `orVrc` p a)
187 timesVrc :: (Bool,Bool) -> (Bool,Bool) -> (Bool,Bool)
188 timesVrc (p1,m1) (p2,m2) = (p1 && p2 || m1 && m2,
189 p1 && m2 || m1 && p2)