Type synonym for a type-modifying prism.

Type synonym for a type-preserving prism.

Build a prism from a constructor and a matcher, which must respect the well-formedness laws.

If you want to build a Prism from the van Laarhoven representation, use prismVL from the optics-vl package.

This is usually used to build a Prism', when you have to use an operation like cast which already returns a Maybe.

This Prism compares for exact equality with a given value.

>>> only 4 # ()
4

>>> 5 ^? only 4
Nothing

This Prism compares for approximate equality with a given value and a predicate for testing, an example where the value is the empty list and the predicate checks that a list is empty (same as _Empty with the AsEmpty list instance):

>>> nearly [] null # ()
[]
>>> [1,2,3,4] ^? nearly [] null
Nothing

nearly [] null :: Prism' [a] ()

To comply with the Prism laws the arguments you supply to nearly a p are somewhat constrained.

We assume p x holds iff x ≡ a. Under that assumption then this is a valid Prism.

This is useful when working with a type where you can test equality for only a subset of its values, and the prism selects such a value.

Work with a Prism as a constructor and a matcher.

Use a Prism to work over part of a structure.

Given a pair of prisms, project sums.

Viewing a Prism as a co-Lens, this combinator can be seen to be dual to alongside.

Lift a Prism through a Traversable functor, giving a Prism that matches only if all the elements of the container match the Prism.

Tag for a prism.