2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[Bags]{@Bag@: an unordered collection with duplicates}
10 emptyBag, unitBag, unionBags, unionManyBags,
12 filterBag, partitionBag, concatBag, foldBag,
13 isEmptyBag, consBag, snocBag,
14 listToBag, bagToList, bagToList_append
20 import Outputable ( interpp'SP )
27 | TwoBags (Bag a) (Bag a) -- The ADT guarantees that at least
28 -- one branch is non-empty
29 | ListBag [a] -- The list is non-empty
30 | ListOfBags [Bag a] -- The list is non-empty
35 elemBag :: Eq a => a -> Bag a -> Bool
37 elemBag x EmptyBag = False
38 elemBag x (UnitBag y) = x==y
39 elemBag x (TwoBags b1 b2) = x `elemBag` b1 || x `elemBag` b2
40 elemBag x (ListBag ys) = any (x ==) ys
41 elemBag x (ListOfBags bs) = any (x `elemBag`) bs
43 unionManyBags [] = EmptyBag
44 unionManyBags xs = ListOfBags xs
46 -- This one is a bit stricter! The bag will get completely evaluated.
48 unionBags EmptyBag b = b
49 unionBags b EmptyBag = b
50 unionBags b1 b2 = TwoBags b1 b2
52 consBag :: a -> Bag a -> Bag a
53 consBag elt bag = (unitBag elt) `unionBags` bag
54 snocBag :: Bag a -> a -> Bag a
55 snocBag bag elt = bag `unionBags` (unitBag elt)
57 isEmptyBag EmptyBag = True
58 isEmptyBag (UnitBag x) = False
59 isEmptyBag (TwoBags b1 b2) = isEmptyBag b1 && isEmptyBag b2 -- Paranoid, but safe
60 isEmptyBag (ListBag xs) = null xs -- Paranoid, but safe
61 isEmptyBag (ListOfBags bs) = all isEmptyBag bs
63 filterBag :: (a -> Bool) -> Bag a -> Bag a
64 filterBag pred EmptyBag = EmptyBag
65 filterBag pred b@(UnitBag val) = if pred val then b else EmptyBag
66 filterBag pred (TwoBags b1 b2) = sat1 `unionBags` sat2
68 sat1 = filterBag pred b1
69 sat2 = filterBag pred b2
70 filterBag pred (ListBag vs) = listToBag (filter pred vs)
71 filterBag pred (ListOfBags bs) = ListOfBags sats
73 sats = [filterBag pred b | b <- bs]
75 concatBag :: Bag (Bag a) -> Bag a
77 concatBag EmptyBag = EmptyBag
78 concatBag (UnitBag b) = b
79 concatBag (TwoBags b1 b2) = concatBag b1 `TwoBags` concatBag b2
80 concatBag (ListBag bs) = ListOfBags bs
81 concatBag (ListOfBags bbs) = ListOfBags (map concatBag bbs)
83 partitionBag :: (a -> Bool) -> Bag a -> (Bag a {- Satisfy predictate -},
85 partitionBag pred EmptyBag = (EmptyBag, EmptyBag)
86 partitionBag pred b@(UnitBag val) = if pred val then (b, EmptyBag) else (EmptyBag, b)
87 partitionBag pred (TwoBags b1 b2) = (sat1 `unionBags` sat2, fail1 `unionBags` fail2)
89 (sat1,fail1) = partitionBag pred b1
90 (sat2,fail2) = partitionBag pred b2
91 partitionBag pred (ListBag vs) = (listToBag sats, listToBag fails)
93 (sats,fails) = partition pred vs
94 partitionBag pred (ListOfBags bs) = (ListOfBags sats, ListOfBags fails)
96 (sats, fails) = unzip [partitionBag pred b | b <- bs]
99 foldBag :: (r -> r -> r) -- Replace TwoBags with this; should be associative
100 -> (a -> r) -- Replace UnitBag with this
101 -> r -- Replace EmptyBag with this
105 {- Standard definition
106 foldBag t u e EmptyBag = e
107 foldBag t u e (UnitBag x) = u x
108 foldBag t u e (TwoBags b1 b2) = (foldBag t u e b1) `t` (foldBag t u e b2)
109 foldBag t u e (ListBag xs) = foldr (t.u) e xs
110 foldBag t u e (ListOfBags bs) = foldr (\b r -> foldBag e u t b `t` r) e bs
113 -- More tail-recursive definition, exploiting associativity of "t"
114 foldBag t u e EmptyBag = e
115 foldBag t u e (UnitBag x) = u x `t` e
116 foldBag t u e (TwoBags b1 b2) = foldBag t u (foldBag t u e b2) b1
117 foldBag t u e (ListBag xs) = foldr (t.u) e xs
118 foldBag t u e (ListOfBags bs) = foldr (\b r -> foldBag t u r b) e bs
121 mapBag :: (a -> b) -> Bag a -> Bag b
122 mapBag f EmptyBag = EmptyBag
123 mapBag f (UnitBag x) = UnitBag (f x)
124 mapBag f (TwoBags b1 b2) = TwoBags (mapBag f b1) (mapBag f b2)
125 mapBag f (ListBag xs) = ListBag (map f xs)
126 mapBag f (ListOfBags bs) = ListOfBags (map (mapBag f) bs)
129 listToBag :: [a] -> Bag a
130 listToBag [] = EmptyBag
131 listToBag vs = ListBag vs
133 bagToList :: Bag a -> [a]
134 bagToList EmptyBag = []
135 bagToList (ListBag vs) = vs
136 bagToList b = bagToList_append b []
138 -- (bagToList_append b xs) flattens b and puts xs on the end.
139 bagToList_append EmptyBag xs = xs
140 bagToList_append (UnitBag x) xs = x:xs
141 bagToList_append (TwoBags b1 b2) xs = bagToList_append b1 (bagToList_append b2 xs)
142 bagToList_append (ListBag xx) xs = xx++xs
143 bagToList_append (ListOfBags bs) xs = foldr bagToList_append xs bs
149 instance (Outputable a) => Outputable (Bag a) where
150 ppr sty EmptyBag = ppStr "emptyBag"
151 ppr sty (UnitBag a) = ppr sty a
152 ppr sty (TwoBags b1 b2) = ppCat [ppr sty b1, pp'SP, ppr sty b2]
153 ppr sty (ListBag as) = interpp'SP sty as
154 ppr sty (ListOfBags bs) = ppCat [ppLbrack, interpp'SP sty bs, ppRbrack]
156 #endif {- COMPILING_GHC -}