foldr

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 :: (Char -> a -> a) -> a -> Text -> a
text Data.Text, text Data.Text.Lazy
O(n) foldr, applied to a binary operator, a starting value (typically the right-identity of the operator), and a Text, reduces the Text using the binary operator, from right to left. Subject to fusion.
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 :: (Char -> Char -> Char) -> Text -> Char
text Data.Text, text Data.Text.Lazy
O(n) A variant of foldr that has no starting value argument, and thus must be applied to a non-empty Text. Subject to fusion.
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.
foldrChunks :: (Text -> a -> a) -> a -> Text -> a
text Data.Text.Lazy.Internal, text Data.Text.Lazy
Consume the chunks of a lazy Text 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 (Char, a)) -> a -> Text
text Data.Text.Lazy
O(n), unfoldr function is analogous to the List unfoldr. unfoldr builds a Text from a seed value. The function takes the element and returns Nothing if it is done producing the Text, otherwise Just (a,b). In this case, a is the next Char in the string, and b is the seed value for further production. Performs replacement on invalid scalar values.
unfoldr :: (a -> Maybe (Char, a)) -> a -> Text
text Data.Text
O(n), unfoldr function is analogous to the List unfoldr. unfoldr builds a Text from a seed value. The function takes the element and returns Nothing if it is done producing the Text, otherwise Just (a,b). In this case, a is the next Char in the string, and b is the seed value for further production. Subject to fusion. Performs replacement on invalid scalar values.
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.

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