-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/
-- | Basic lens type and functions
--
-- Necessary type and functions for basic lens work.
--
-- Handy to depend on for libraries and general light-weight use,
-- including PITA environments, old GHCs and non-GHC implementations with
-- Rank-N type support. Depends on only on base.
@package basic-lens
@version 0.0.2
-- | Basic lens type and functions.
--
-- The lens package should be a drop-in replacement for this.
module Control.Lens.Basic
-- | Purpose
--
-- A value of type Lens s t a b provides the following:
--
--
-- - A reference into the structure s to read and update the
-- value a inside it.
-- - The possibility to change the type of s to t and
-- the type of a to b.
--
--
-- The Functor constraint
--
-- Operations may do something more interesting inside the f
-- functor. For the purpose of this module and package, all the functions
-- below (view, over, set) use a no-op functor and
-- therefore the above type is equivalent to:
--
--
-- type Lens s t a b = (a -> b) -> (s -> t)
--
--
-- But it is left generic for forward compatibilty with the lens package.
--
-- Example
--
--
-- λ> data Person = Person { personChar :: Char, personAge :: Int } deriving Show
-- λ> view $(field 'personChar) (Person a 10)
-- a
-- λ> over $(field 'personAge) (*2) (Person a 10)
-- Person {personChar = a, personAge = 20}
-- λ>
--
--
-- Laws
--
-- 1) Get-Put: You get back what you put in.
--
--
-- view l (set l v s) ≡ v
--
--
-- 2) Put-Get: Putting back what you got doesn't change anything.
--
--
-- set l (view l s) s ≡ s
--
--
-- 3) Put-Put: Setting is idempotent.
--
--
-- set l v (set l v s) ≡ set l v s
--
type Lens s t a b = forall f. Functor f => (a -> f b) -> (s -> f t)
-- | Get the a inside the s.
view :: Lens s t a b -> s -> a
-- | Set the a inside the s, optionally changing the
-- types to b and t.
set :: Lens s t a b -> b -> s -> t
-- | Modify the a inside the s, optionally changing the
-- types to b and t.
over :: Lens s t a b -> (a -> b) -> s -> t
-- | Make a lens from a field name.
--
-- Example: over $(field 'foo) (*2)
field :: Name -> Q Exp
instance GHC.Base.Functor Control.Lens.Basic.Id