Control.Lens.Properties

A collection of properties that can be tested with QuickCheck, to guarantee that you are working with valid Lenses, Setters, Traversals, Isos and Prisms.

Documentation

isLens :: (Arbitrary s, Arbitrary a, CoArbitrary a, Show s, Show a, Eq s, Eq a, Function a) => Lens' s a -> Property

A Lens is only legal if it is a valid Traversal (see isTraversal for what this means), and if the following laws hold:

1. view l (set l b a)  ≡ b

2. set l (view l a) a  ≡ a

3. set l c (set l b a) ≡ set l c a

isTraversal :: (Arbitrary s, Arbitrary a, CoArbitrary a, Show s, Show a, Eq s, Function a) => Traversal' s a -> Property

A Traversal is only legal if it is a valid Setter (see isSetter for what makes a Setter valid), and the following laws hold:

1. t pure ≡ pure

2. fmap (t f) . t g ≡ getCompose . t (Compose . fmap f . g)

isSetter :: (Arbitrary s, Arbitrary a, CoArbitrary a, Show s, Show a, Eq s, Function a) => Setter' s a -> Property

A Setter is only legal if the following 3 laws hold:

1. set l y (set l x a) ≡ set l y a

2. over l id ≡ id

3. over l f . over l g ≡ over l (f . g)

isIso :: (Arbitrary s, Arbitrary a, CoArbitrary s, CoArbitrary a, Show s, Show a, Eq s, Eq a, Function s, Function a) => Iso' s a -> Property

isPrism :: (Arbitrary s, Arbitrary a, CoArbitrary a, Show s, Show a, Eq s, Eq a, Function a) => Prism' s a -> Property