--- /dev/null
+%
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
+%
+\section[Bags]{@Bag@: an unordered collection with duplicates}
+
+\begin{code}
+module Bag (
+ Bag, -- abstract type
+
+ emptyBag, unitBag, unionBags, unionManyBags,
+ mapBag,
+ elemBag,
+ filterBag, partitionBag, concatBag, foldBag, foldrBag, foldlBag,
+ isEmptyBag, isSingletonBag, consBag, snocBag, anyBag,
+ listToBag, bagToList,
+ mapBagM, mapAndUnzipBagM
+ ) where
+
+#include "HsVersions.h"
+
+import Outputable
+import Util ( isSingleton )
+import List ( partition )
+\end{code}
+
+
+\begin{code}
+data Bag a
+ = EmptyBag
+ | UnitBag a
+ | TwoBags (Bag a) (Bag a) -- INVARIANT: neither branch is empty
+ | ListBag [a] -- INVARIANT: the list is non-empty
+
+emptyBag = EmptyBag
+unitBag = UnitBag
+
+elemBag :: Eq a => a -> Bag a -> Bool
+
+elemBag x EmptyBag = False
+elemBag x (UnitBag y) = x==y
+elemBag x (TwoBags b1 b2) = x `elemBag` b1 || x `elemBag` b2
+elemBag x (ListBag ys) = any (x ==) ys
+
+unionManyBags :: [Bag a] -> Bag a
+unionManyBags xs = foldr unionBags EmptyBag xs
+
+-- This one is a bit stricter! The bag will get completely evaluated.
+
+unionBags :: Bag a -> Bag a -> Bag a
+unionBags EmptyBag b = b
+unionBags b EmptyBag = b
+unionBags b1 b2 = TwoBags b1 b2
+
+consBag :: a -> Bag a -> Bag a
+snocBag :: Bag a -> a -> Bag a
+
+consBag elt bag = (unitBag elt) `unionBags` bag
+snocBag bag elt = bag `unionBags` (unitBag elt)
+
+isEmptyBag EmptyBag = True
+isEmptyBag other = False -- NB invariants
+
+isSingletonBag :: Bag a -> Bool
+isSingletonBag EmptyBag = False
+isSingletonBag (UnitBag x) = True
+isSingletonBag (TwoBags b1 b2) = False -- Neither is empty
+isSingletonBag (ListBag xs) = isSingleton xs
+
+filterBag :: (a -> Bool) -> Bag a -> Bag a
+filterBag pred EmptyBag = EmptyBag
+filterBag pred b@(UnitBag val) = if pred val then b else EmptyBag
+filterBag pred (TwoBags b1 b2) = sat1 `unionBags` sat2
+ where
+ sat1 = filterBag pred b1
+ sat2 = filterBag pred b2
+filterBag pred (ListBag vs) = listToBag (filter pred vs)
+
+anyBag :: (a -> Bool) -> Bag a -> Bool
+anyBag p EmptyBag = False
+anyBag p (UnitBag v) = p v
+anyBag p (TwoBags b1 b2) = anyBag p b1 || anyBag p b2
+anyBag p (ListBag xs) = any p xs
+
+concatBag :: Bag (Bag a) -> Bag a
+concatBag EmptyBag = EmptyBag
+concatBag (UnitBag b) = b
+concatBag (TwoBags b1 b2) = concatBag b1 `unionBags` concatBag b2
+concatBag (ListBag bs) = unionManyBags bs
+
+partitionBag :: (a -> Bool) -> Bag a -> (Bag a {- Satisfy predictate -},
+ Bag a {- Don't -})
+partitionBag pred EmptyBag = (EmptyBag, EmptyBag)
+partitionBag pred b@(UnitBag val) = if pred val then (b, EmptyBag) else (EmptyBag, b)
+partitionBag pred (TwoBags b1 b2) = (sat1 `unionBags` sat2, fail1 `unionBags` fail2)
+ where
+ (sat1,fail1) = partitionBag pred b1
+ (sat2,fail2) = partitionBag pred b2
+partitionBag pred (ListBag vs) = (listToBag sats, listToBag fails)
+ where
+ (sats,fails) = partition pred vs
+
+
+foldBag :: (r -> r -> r) -- Replace TwoBags with this; should be associative
+ -> (a -> r) -- Replace UnitBag with this
+ -> r -- Replace EmptyBag with this
+ -> Bag a
+ -> r
+
+{- Standard definition
+foldBag t u e EmptyBag = e
+foldBag t u e (UnitBag x) = u x
+foldBag t u e (TwoBags b1 b2) = (foldBag t u e b1) `t` (foldBag t u e b2)
+foldBag t u e (ListBag xs) = foldr (t.u) e xs
+-}
+
+-- More tail-recursive definition, exploiting associativity of "t"
+foldBag t u e EmptyBag = e
+foldBag t u e (UnitBag x) = u x `t` e
+foldBag t u e (TwoBags b1 b2) = foldBag t u (foldBag t u e b2) b1
+foldBag t u e (ListBag xs) = foldr (t.u) e xs
+
+foldrBag :: (a -> r -> r) -> r
+ -> Bag a
+ -> r
+
+foldrBag k z EmptyBag = z
+foldrBag k z (UnitBag x) = k x z
+foldrBag k z (TwoBags b1 b2) = foldrBag k (foldrBag k z b2) b1
+foldrBag k z (ListBag xs) = foldr k z xs
+
+foldlBag :: (r -> a -> r) -> r
+ -> Bag a
+ -> r
+
+foldlBag k z EmptyBag = z
+foldlBag k z (UnitBag x) = k z x
+foldlBag k z (TwoBags b1 b2) = foldlBag k (foldlBag k z b1) b2
+foldlBag k z (ListBag xs) = foldl k z xs
+
+
+mapBag :: (a -> b) -> Bag a -> Bag b
+mapBag f EmptyBag = EmptyBag
+mapBag f (UnitBag x) = UnitBag (f x)
+mapBag f (TwoBags b1 b2) = TwoBags (mapBag f b1) (mapBag f b2)
+mapBag f (ListBag xs) = ListBag (map f xs)
+
+mapBagM :: Monad m => (a -> m b) -> Bag a -> m (Bag b)
+mapBagM f EmptyBag = return EmptyBag
+mapBagM f (UnitBag x) = do { r <- f x; return (UnitBag r) }
+mapBagM f (TwoBags b1 b2) = do { r1 <- mapBagM f b1; r2 <- mapBagM f b2; return (TwoBags r1 r2) }
+mapBagM f (ListBag xs) = do { rs <- mapM f xs; return (ListBag rs) }
+
+mapAndUnzipBagM :: Monad m => (a -> m (b,c)) -> Bag a -> m (Bag b, Bag c)
+mapAndUnzipBagM f EmptyBag = return (EmptyBag, EmptyBag)
+mapAndUnzipBagM f (UnitBag x) = do { (r,s) <- f x; return (UnitBag r, UnitBag s) }
+mapAndUnzipBagM f (TwoBags b1 b2) = do { (r1,s1) <- mapAndUnzipBagM f b1
+ ; (r2,s2) <- mapAndUnzipBagM f b2
+ ; return (TwoBags r1 r2, TwoBags s1 s2) }
+mapAndUnzipBagM f (ListBag xs) = do { ts <- mapM f xs
+ ; let (rs,ss) = unzip ts
+ ; return (ListBag rs, ListBag ss) }
+
+listToBag :: [a] -> Bag a
+listToBag [] = EmptyBag
+listToBag vs = ListBag vs
+
+bagToList :: Bag a -> [a]
+bagToList b = foldrBag (:) [] b
+\end{code}
+
+\begin{code}
+instance (Outputable a) => Outputable (Bag a) where
+ ppr EmptyBag = ptext SLIT("emptyBag")
+ ppr (UnitBag a) = ppr a
+ ppr (TwoBags b1 b2) = hsep [ppr b1 <> comma, ppr b2]
+ ppr (ListBag as) = interpp'SP as
+\end{code}
projects / ghc-hetmet.git / blobdiff