Optics.IxFold

Type synonym for an indexed fold.

Obtain an indexed fold by lifting itraverse_ like function.

ifoldVL . itraverseOf_ ≡ id
itraverseOf_ . ifoldVL ≡ id

Fold with index via embedding into a monoid.

Fold with index right-associatively.

Fold with index left-associatively, and strictly.

Fold with index to a list.

>>> itoListOf (folded % ifolded) ["abc", "def"][(0,'a'),(1,'b'),(2,'c'),(0,'d'),(1,'e'),(2,'f')]

Note: currently indexed optics can be used as non-indexed.

>>> toListOf (folded % ifolded) ["abc", "def"]"abcdef"

Traverse over all of the targets of an IxFold, computing an Applicative-based answer, but unlike itraverseOf do not construct a new structure.

>>> itraverseOf_ each (curry print) ("hello","world")(0,"hello")(1,"world")

A version of itraverseOf_ with the arguments flipped.

Indexed fold via FoldableWithIndex class.

Obtain an IxFold by lifting an operation that returns a FoldableWithIndex result.

This can be useful to lift operations from Data.List and elsewhere into an IxFold.

>>> itoListOf (ifolding words) "how are you"[(0,"how"),(1,"are"),(2,"you")]

Obtain an IxFold by lifting ifoldr like function.

>>> itoListOf (ifoldring ifoldr) "hello"[(0,'h'),(1,'e'),(2,'l'),(3,'l'),(4,'o')]

Retrieve the first entry of an IxFold along with its index.

>>> iheadOf ifolded [1..10]Just (0,1)

Retrieve the last entry of an IxFold along with its index.

>>> ilastOf ifolded [1..10]Just (9,10)

Return whether or not any element viewed through an IxFold satisfies a predicate, with access to the i.

When you don't need access to the index then anyOf is more flexible in what it accepts.

anyOf o ≡ ianyOf o . const

Return whether or not all elements viewed through an IxFold satisfy a predicate, with access to the i.

When you don't need access to the index then allOf is more flexible in what it accepts.

allOf o ≡ iallOf o . const

Return whether or not none of the elements viewed through an IxFold satisfy a predicate, with access to the i.

When you don't need access to the index then noneOf is more flexible in what it accepts.

noneOf o ≡ inoneOf o . const

The ifindOf function takes an IxFold, a predicate that is also supplied the index, a structure and returns the left-most element of the structure along with its index matching the predicate, or Nothing if there is no such element.

When you don't need access to the index then findOf is more flexible in what it accepts.

The ifindMOf function takes an IxFold, a monadic predicate that is also supplied the index, a structure and returns in the monad the left-most element of the structure matching the predicate, or Nothing if there is no such element.

When you don't need access to the index then findMOf is more flexible in what it accepts.

Convert an indexed fold to an IxAffineFold that visits the first element of the original fold.

For the traversal version see isingular.

Filter results of an IxFold that don't satisfy a predicate.

>>> toListOf (ifolded %& ifiltered (>)) [3,2,1,0][1,0]

This allows you to traverse the elements of an IxFold in the opposite order.

Return entries of the first IxFold, then the second one.

>>> itoListOf (ifolded `isumming` ibackwards_ ifolded) ["a","b"][(0,"a"),(1,"b"),(1,"b"),(0,"a")]

For the traversal version see iadjoin.

Try the first IxFold. If it returns no entries, try the second one.

>>> itoListOf (_1 % ifolded `ifailing` _2 % ifolded) (["a"], ["b","c"])[(0,"a")]>>> itoListOf (_1 % ifolded `ifailing` _2 % ifolded) ([], ["b","c"])[(0,"b"),(1,"c")]

Tag for a fold.

A container that supports folding with an additional index.