# foldr -text -containers

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, 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, 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.
foldr1 is a variant of foldr that has no starting value argument, and thus must be applied to non-empty lists.
Fold over the elements of a structure, associating to the right, but strictly.
Monadic fold over the elements of a structure, associating to the right, i.e. from right to left.
'foldr\'' is a strict variant of foldr
'foldr\'' is like foldr, but strict in the accumulator.
foldr1 is a variant of foldr that has no starting value argument, and thus must be applied to non-empty ByteStrings
foldr1 is a variant of foldr that has no starting value argument, and thus must be applied to non-empty ByteStrings
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.
A strict variant of foldr1
'foldr1\'' is a variant of foldr1, but is strict in the accumulator.
Consume the chunks of a lazy ByteString with a natural right fold.
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]
Create a Builder that encodes a sequence generated from a seed value using a BoundedPrim for each sequence element.
Encode a list of values represented as an unfoldr with a FixedPrim.
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.