foldr -text

foldr :: (a -> b -> b) -> b -> [a] -> b
base Prelude, base Data.List
foldr, applied to a binary operator, a starting value (typically the right-identity of the operator), and a list, reduces the list using the binary operator, from right to left: > foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)
foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b
base Data.Foldable
foldr :: (Char -> a -> a) -> a -> ByteString -> a
bytestring Data.ByteString.Char8, bytestring Data.ByteString.Lazy.Char8
foldr, applied to a binary operator, a starting value (typically the right-identity of the operator), and a packed string, reduces the packed string using the binary operator, from right to left.
foldr :: (Key -> b -> b) -> b -> IntSet -> b
containers Data.IntSet
O(n). Fold the elements in the set using the given right-associative binary operator, such that foldr f z == foldr f z . toAscList. For example, > toAscList set = foldr (:) [] set
foldr :: (Word8 -> a -> a) -> a -> ByteString -> a
bytestring Data.ByteString, bytestring Data.ByteString.Lazy
foldr, applied to a binary operator, a starting value (typically the right-identity of the operator), and a ByteString, reduces the ByteString using the binary operator, from right to left.
foldr :: (a -> b -> b) -> b -> IntMap a -> b
containers Data.IntMap.Strict, containers Data.IntMap.Lazy
O(n). Fold the values in the map using the given right-associative binary operator, such that foldr f z == foldr f z . elems. For example, > elems map = foldr (:) [] map > let f a len = len + (length a) > foldr f 0 (fromList [(5,"a"), (3,"bbb")]) == 4
foldr :: (a -> b -> b) -> b -> Map k a -> b
containers Data.Map.Lazy, containers Data.Map.Strict
O(n). Fold the values in the map using the given right-associative binary operator, such that foldr f z == foldr f z . elems. For example, > elems map = foldr (:) [] map > let f a len = len + (length a) > foldr f 0 (fromList [(5,"a"), (3,"bbb")]) == 4
foldr :: (a -> b -> b) -> b -> Set a -> b
containers Data.Set
O(n). Fold the elements in the set using the given right-associative binary operator, such that foldr f z == foldr f z . toAscList. For example, > toAscList set = foldr (:) [] set
foldr1 :: (a -> a -> a) -> [a] -> a
base Prelude, base Data.List
foldr1 is a variant of foldr that has no starting value argument, and thus must be applied to non-empty lists.
foldr' :: Foldable t => (a -> b -> b) -> b -> t a -> b
base Data.Foldable
Fold over the elements of a structure, associating to the right, but strictly.
foldr1 :: Foldable t => (a -> a -> a) -> t a -> a
base Data.Foldable
foldrM :: (Foldable t, Monad m) => (a -> b -> m b) -> b -> t a -> m b
base Data.Foldable
Monadic fold over the elements of a structure, associating to the right, i.e. from right to left.
foldr' :: (Char -> a -> a) -> a -> ByteString -> a
bytestring Data.ByteString.Char8
'foldr\'' is a strict variant of foldr
foldr' :: (Key -> b -> b) -> b -> IntSet -> b
containers Data.IntSet
O(n). A strict version of foldr. Each application of the operator is evaluated before using the result in the next application. This function is strict in the starting value.
foldr' :: (Word8 -> a -> a) -> a -> ByteString -> a
bytestring Data.ByteString
'foldr\'' is like foldr, but strict in the accumulator.
foldr' :: (a -> b -> b) -> b -> IntMap a -> b
containers Data.IntMap.Strict, containers Data.IntMap.Lazy
O(n). A strict version of foldr. Each application of the operator is evaluated before using the result in the next application. This function is strict in the starting value.
foldr' :: (a -> b -> b) -> b -> Map k a -> b
containers Data.Map.Lazy, containers Data.Map.Strict
O(n). A strict version of foldr. Each application of the operator is evaluated before using the result in the next application. This function is strict in the starting value.
foldr' :: (a -> b -> b) -> b -> Set a -> b
containers Data.Set
O(n). A strict version of foldr. Each application of the operator is evaluated before using the result in the next application. This function is strict in the starting value.
foldr1 :: (Char -> Char -> Char) -> ByteString -> Char
bytestring Data.ByteString.Char8, bytestring Data.ByteString.Lazy.Char8
foldr1 is a variant of foldr that has no starting value argument, and thus must be applied to non-empty ByteStrings
foldr1 :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8
bytestring Data.ByteString.Lazy
foldr1 is a variant of foldr that has no starting value argument, and thus must be applied to non-empty ByteStrings
foldr1 :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8
bytestring Data.ByteString
foldr1 is a variant of foldr that has no starting value argument, and thus must be applied to non-empty ByteStrings An exception will be thrown in the case of an empty ByteString.
foldr1' :: (Char -> Char -> Char) -> ByteString -> Char
bytestring Data.ByteString.Char8
A strict variant of foldr1
foldr1' :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8
bytestring Data.ByteString
'foldr1\'' is a variant of foldr1, but is strict in the accumulator.
foldrChunks :: (ByteString -> a -> a) -> a -> ByteString -> a
bytestring Data.ByteString.Lazy
Consume the chunks of a lazy ByteString with a natural right fold.
foldrWithIndex :: (Int -> a -> b -> b) -> b -> Seq a -> b
containers Data.Sequence
foldrWithIndex is a version of foldr that also provides access to the index of each element.
foldrWithKey :: (Key -> a -> b -> b) -> b -> IntMap a -> b
containers Data.IntMap.Strict, containers Data.IntMap.Lazy
O(n). Fold the keys and values in the map using the given right-associative binary operator, such that foldrWithKey f z == foldr (uncurry f) z . toAscList. For example, > keys map = foldrWithKey (\k x ks -> k:ks) [] map > let f k a result = result ++ "(" ++ (show k) ++ ":" ++ a ++ ")" > foldrWithKey f "Map: " (fromList [(5,"a"), (3,"b")]) == "Map: (5:a)(3:b)"
foldrWithKey :: (k -> a -> b -> b) -> b -> Map k a -> b
containers Data.Map.Lazy, containers Data.Map.Strict
O(n). Fold the keys and values in the map using the given right-associative binary operator, such that foldrWithKey f z == foldr (uncurry f) z . toAscList. For example, > keys map = foldrWithKey (\k x ks -> k:ks) [] map > let f k a result = result ++ "(" ++ (show k) ++ ":" ++ a ++ ")" > foldrWithKey f "Map: " (fromList [(5,"a"), (3,"b")]) == "Map: (5:a)(3:b)"
foldrWithKey' :: (Key -> a -> b -> b) -> b -> IntMap a -> b
containers Data.IntMap.Strict, containers Data.IntMap.Lazy
O(n). A strict version of foldrWithKey. Each application of the operator is evaluated before using the result in the next application. This function is strict in the starting value.
foldrWithKey' :: (k -> a -> b -> b) -> b -> Map k a -> b
containers Data.Map.Lazy, containers Data.Map.Strict
O(n). A strict version of foldrWithKey. Each application of the operator is evaluated before using the result in the next application. This function is strict in the starting value.
unfoldr :: (b -> Maybe (a, b)) -> b -> [a]
base Data.List
The unfoldr function is a `dual' to foldr: while foldr reduces a list to a summary value, unfoldr builds a list from a seed value. The function takes the element and returns Nothing if it is done producing the list or returns Just (a,b), in which case, a is a prepended to the list and b is used as the next element in a recursive call. For example, > iterate f == unfoldr (\x -> Just (x, f x)) In some cases, unfoldr can undo a foldr operation: > unfoldr f' (foldr f z xs) == xs if the following holds: > f' (f x y) = Just (x,y) > f' z = Nothing A simple use of unfoldr: > unfoldr (\b -> if b == 0 then Nothing else Just (b, b-1)) 10 > [10,9,8,7,6,5,4,3,2,1]
primUnfoldrBounded :: BoundedPrim b -> (a -> Maybe (b, a)) -> a -> Builder
bytestring Data.ByteString.Builder.Prim
Create a Builder that encodes a sequence generated from a seed value using a BoundedPrim for each sequence element.
primUnfoldrFixed :: FixedPrim b -> (a -> Maybe (b, a)) -> a -> Builder
bytestring Data.ByteString.Builder.Prim
Encode a list of values represented as an unfoldr with a FixedPrim.
unfoldr :: (a -> Maybe (Char, a)) -> a -> ByteString
bytestring Data.ByteString.Lazy.Char8
O(n) The unfoldr function is analogous to the List 'unfoldr'. unfoldr builds a ByteString from a seed value. The function takes the element and returns Nothing if it is done producing the ByteString or returns Just (a,b), in which case, a is a prepending to the ByteString and b is used as the next element in a recursive call.
unfoldr :: (a -> Maybe (Char, a)) -> a -> ByteString
bytestring Data.ByteString.Char8
O(n), unfoldr function is analogous to the List 'unfoldr'. unfoldr builds a ByteString from a seed value. The function takes the element and returns Nothing if it is done producing the ByteString or returns Just (a,b), in which case, a is the next character in the string, and b is the seed value for further production. Examples: > unfoldr (\x -> if x <= '9' then Just (x, succ x) else Nothing) '0' == "0123456789"
unfoldr :: (a -> Maybe (Word8, a)) -> a -> ByteString
bytestring Data.ByteString.Lazy
O(n) The unfoldr function is analogous to the List 'unfoldr'. unfoldr builds a ByteString from a seed value. The function takes the element and returns Nothing if it is done producing the ByteString or returns Just (a,b), in which case, a is a prepending to the ByteString and b is used as the next element in a recursive call.
unfoldr :: (a -> Maybe (Word8, a)) -> a -> ByteString
bytestring Data.ByteString
O(n), unfoldr function is analogous to the List 'unfoldr'. unfoldr builds a ByteString from a seed value. The function takes the element and returns Nothing if it is done producing the ByteString or returns Just (a,b), in which case, a is the next byte in the string, and b is the seed value for further production. Examples: > unfoldr (\x -> if x <= 5 then Just (x, x + 1) else Nothing) 0 > == pack [0, 1, 2, 3, 4, 5]
unfoldr :: (b -> Maybe (a, b)) -> b -> Seq a
containers Data.Sequence
Builds a sequence from a seed value. Takes time linear in the number of generated elements. WARNING: If the number of generated elements is infinite, this method will not terminate.
unfoldrN :: Int -> (a -> Maybe (Char, a)) -> a -> (ByteString, Maybe a)
bytestring Data.ByteString.Char8
O(n) Like unfoldr, unfoldrN builds a ByteString from a seed value. However, the length of the result is limited by the first argument to unfoldrN. This function is more efficient than unfoldr when the maximum length of the result is known. The following equation relates unfoldrN and unfoldr: > unfoldrN n f s == take n (unfoldr f s)
unfoldrN :: Int -> (a -> Maybe (Word8, a)) -> a -> (ByteString, Maybe a)
bytestring Data.ByteString
O(n) Like unfoldr, unfoldrN builds a ByteString from a seed value. However, the length of the result is limited by the first argument to unfoldrN. This function is more efficient than unfoldr when the maximum length of the result is known. The following equation relates unfoldrN and unfoldr: > fst (unfoldrN n f s) == take n (unfoldr f s)