import MkCore
import DsMonad
import DsUtils
-import Util ( takeList )
+import Util ( all2, takeList, zipEqual )
+import ListSetOps ( runs )
import Id
-import Var (TyVar)
+import Var ( Var )
+import NameEnv
import SrcLoc
import Outputable
\end{code}
= do { alts <- mapM (matchOneCon vars ty) groups
; return (mkCoAlgCaseMatchResult var ty alts) }
+type ConArgPats = HsConDetails (LPat Id) (HsRecFields Id (LPat Id))
+
matchOneCon :: [Id]
-> Type
-> [EquationInfo]
- -> DsM (DataCon, [TyVar], MatchResult)
+ -> DsM (DataCon, [Var], MatchResult)
matchOneCon vars ty (eqn1 : eqns) -- All eqns for a single constructor
- = do { (wraps, eqns') <- mapAndUnzipM shift (eqn1:eqns)
- ; arg_vars <- selectMatchVars (take (dataConSourceArity con1)
- (eqn_pats (head eqns')))
- -- Use the new argument patterns as a source of
+ = do { arg_vars <- selectConMatchVars arg_tys args1
+ -- Use the first equation as a source of
-- suggestions for the new variables
- ; match_result <- match (arg_vars ++ vars) ty eqns'
+
+ -- Divide into sub-groups; see Note [Record patterns]
+ ; let groups :: [[(ConArgPats, EquationInfo)]]
+ groups = runs compatible_pats [ (pat_args (firstPat eqn), eqn)
+ | eqn <- eqn1:eqns ]
+
+ ; match_results <- mapM (match_group arg_vars) groups
+
; return (con1, tvs1 ++ dicts1 ++ arg_vars,
- adjustMatchResult (foldr1 (.) wraps) match_result) }
+ foldr1 combineMatchResults match_results) }
where
ConPatOut { pat_con = L _ con1, pat_ty = pat_ty1,
- pat_tvs = tvs1, pat_dicts = dicts1 } = firstPat eqn1
+ pat_tvs = tvs1, pat_dicts = dicts1, pat_args = args1 }
+ = firstPat eqn1
+ fields1 = dataConFieldLabels con1
arg_tys = dataConInstOrigArgTys con1 inst_tys
inst_tys = tcTyConAppArgs pat_ty1 ++
-- dataConInstOrigArgTys takes the univ and existential tyvars
-- and returns the types of the *value* args, which is what we want
- shift eqn@(EqnInfo { eqn_pats = ConPatOut{ pat_tvs = tvs, pat_dicts = ds,
- pat_binds = bind, pat_args = args
- } : pats })
- = do { prs <- dsLHsBinds bind
- ; return (wrapBinds (tvs `zip` tvs1)
- . wrapBinds (ds `zip` dicts1)
- . mkCoreLet (Rec prs),
- eqn { eqn_pats = conArgPats con1 arg_tys args ++ pats }) }
-
-conArgPats :: DataCon
- -> [Type] -- Instantiated argument types
+ match_group :: [Id] -> [(ConArgPats, EquationInfo)] -> DsM MatchResult
+ -- All members of the group have compatible ConArgPats
+ match_group arg_vars arg_eqn_prs
+ = do { (wraps, eqns') <- mapAndUnzipM shift arg_eqn_prs
+ ; let group_arg_vars = select_arg_vars arg_vars arg_eqn_prs
+ ; match_result <- match (group_arg_vars ++ vars) ty eqns'
+ ; return (adjustMatchResult (foldr1 (.) wraps) match_result) }
+
+ shift (_, eqn@(EqnInfo { eqn_pats = ConPatOut{ pat_tvs = tvs, pat_dicts = ds,
+ pat_binds = bind, pat_args = args
+ } : pats }))
+ = do { prs <- dsLHsBinds bind
+ ; return (wrapBinds (tvs `zip` tvs1)
+ . wrapBinds (ds `zip` dicts1)
+ . mkCoreLet (Rec prs),
+ eqn { eqn_pats = conArgPats arg_tys args ++ pats }) }
+
+ -- Choose the right arg_vars in the right order for this group
+ -- Note [Record patterns]
+ select_arg_vars arg_vars ((arg_pats, _) : _)
+ | RecCon flds <- arg_pats
+ , let rpats = rec_flds flds
+ , not (null rpats) -- Treated specially; cf conArgPats
+ = ASSERT2( length fields1 == length arg_vars,
+ ppr con1 $$ ppr fields1 $$ ppr arg_vars )
+ map lookup_fld rpats
+ | otherwise
+ = arg_vars
+ where
+ fld_var_env = mkNameEnv $ zipEqual "get_arg_vars" fields1 arg_vars
+ lookup_fld rpat = lookupNameEnv_NF fld_var_env
+ (idName (unLoc (hsRecFieldId rpat)))
+
+-----------------
+compatible_pats :: (ConArgPats,a) -> (ConArgPats,a) -> Bool
+-- Two constructors have compatible argument patterns if the number
+-- and order of sub-matches is the same in both cases
+compatible_pats (RecCon flds1, _) (RecCon flds2, _) = same_fields flds1 flds2
+compatible_pats (RecCon flds1, _) _ = null (rec_flds flds1)
+compatible_pats _ (RecCon flds2, _) = null (rec_flds flds2)
+compatible_pats _ _ = True -- Prefix or infix con
+
+same_fields :: HsRecFields Id (LPat Id) -> HsRecFields Id (LPat Id) -> Bool
+same_fields flds1 flds2
+ = all2 (\f1 f2 -> unLoc (hsRecFieldId f1) == unLoc (hsRecFieldId f2))
+ (rec_flds flds1) (rec_flds flds2)
+
+
+-----------------
+selectConMatchVars :: [Type] -> ConArgPats -> DsM [Id]
+selectConMatchVars arg_tys (RecCon {}) = newSysLocalsDs arg_tys
+selectConMatchVars _ (PrefixCon ps) = selectMatchVars (map unLoc ps)
+selectConMatchVars _ (InfixCon p1 p2) = selectMatchVars [unLoc p1, unLoc p2]
+
+conArgPats :: [Type] -- Instantiated argument types
-- Used only to fill in the types of WildPats, which
-- are probably never looked at anyway
- -> HsConDetails (LPat Id) (HsRecFields Id (LPat Id))
+ -> ConArgPats
-> [Pat Id]
-conArgPats _data_con _arg_tys (PrefixCon ps) = map unLoc ps
-conArgPats _data_con _arg_tys (InfixCon p1 p2) = [unLoc p1, unLoc p2]
-conArgPats data_con arg_tys (RecCon (HsRecFields rpats _))
- | null rpats
- = -- Special case for C {}, which can be used for
- -- a constructor that isn't declared to have
- -- fields at all
- map WildPat arg_tys
-
- | otherwise
- = zipWith mk_pat (dataConFieldLabels data_con) arg_tys
- where
- -- mk_pat picks a WildPat of the appropriate type for absent fields,
- -- and the specified pattern for present fields
- mk_pat lbl arg_ty
- = case [ pat | HsRecField sel_id pat _ <- rpats, idName (unLoc sel_id) == lbl ] of
- (pat:pats) -> ASSERT( null pats ) unLoc pat
- [] -> WildPat arg_ty
+conArgPats _arg_tys (PrefixCon ps) = map unLoc ps
+conArgPats _arg_tys (InfixCon p1 p2) = [unLoc p1, unLoc p2]
+conArgPats arg_tys (RecCon (HsRecFields { rec_flds = rpats }))
+ | null rpats = map WildPat arg_tys
+ -- Important special case for C {}, which can be used for a
+ -- datacon that isn't declared to have fields at all
+ | otherwise = map (unLoc . hsRecFieldArg) rpats
\end{code}
+Note [Record patterns]
+~~~~~~~~~~~~~~~~~~~~~~
+Consider
+ data T = T { x,y,z :: Bool }
+
+ f (T { y=True, x=False }) = ...
+
+We must match the patterns IN THE ORDER GIVEN, thus for the first
+one we match y=True before x=False. See Trac #246; or imagine
+matching against (T { y=False, x=undefined }): should fail without
+touching the undefined.
+
+Now consider:
+
+ f (T { y=True, x=False }) = ...
+ f (T { x=True, y= False}) = ...
+
+In the first we must test y first; in the second we must test x
+first. So we must divide even the equations for a single constructor
+T into sub-goups, based on whether they match the same field in the
+same order. That's what the (runs compatible_pats) grouping.
+
+All non-record patterns are "compatible" in this sense, because the
+positional patterns (T a b) and (a `T` b) all match the arguments
+in order. Also T {} is special because it's equivalent to (T _ _).
+Hence the (null rpats) checks here and there.
+
+
Note [Existentials in shift_con_pat]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
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