Merge pull request #54 from themoritz/non

add non iso

Author: paf31

src/Data/Lens.purs

@@ -22,7 +22,7 @@ module Data.Lens
   , module Data.Lens.Common
   ) where
 
-import Data.Lens.Iso (AnIso, AnIso', Iso, Iso', Optic, Exchange(..), Re(..), au, auf, cloneIso, curried, flipped, iso, re, uncurried, under, withIso)
+import Data.Lens.Iso (AnIso, AnIso', Iso, Iso', Optic, Exchange(..), Re(..), au, auf, cloneIso, non, curried, flipped, iso, re, uncurried, under, withIso)
 import Data.Lens.Lens (ALens, ALens', Lens, Lens', cloneLens, lens, lens', withLens)
 import Data.Lens.Prism (APrism, APrism', Prism, Prism', Review, Review', clonePrism, is, isn't, matching, nearly, only, prism, prism', review, withPrism)
 import Data.Lens.Traversal (Traversal, Traversal', element, elementsOf, failover, itraverseOf, sequenceOf, traverseOf, traversed)

src/Data/Lens/Iso.purs

@@ -1,12 +1,12 @@
 -- | This module defines functions for working with isomorphisms.
 module Data.Lens.Iso
-  ( iso, withIso, cloneIso, re, au, auf, under, curried, uncurried, flipped, mapping, dimapping
+  ( iso, withIso, cloneIso, re, au, auf, under, non, curried, uncurried, flipped, mapping, dimapping
   , module Data.Lens.Types
   ) where
 
 import Prelude
-
 import Data.Lens.Types (Iso, Iso', AnIso, AnIso', Optic, Exchange(..), Re(..))
+import Data.Maybe (Maybe(..), fromMaybe)
 import Data.Profunctor (class Profunctor, dimap, rmap)
 import Data.Tuple (Tuple, curry, uncurry)
 import Data.Newtype (unwrap)
@@ -37,6 +37,11 @@ auf l = withIso l \sa bt f g e -> bt (f (rmap sa g) e)
 under :: forall s t a b. AnIso s t a b -> (t -> s) -> b -> a
 under l = withIso l \sa bt ts -> sa <<< ts <<< bt
 
+non :: forall a. Eq a => a -> Iso' (Maybe a) a
+non def = iso (fromMaybe def) g
+  where g a | a == def  = Nothing
+            | otherwise = Just a
+
 curried :: forall a b c d e f. Iso (Tuple a b -> c) (Tuple d e -> f) (a -> b -> c) (d -> e -> f)
 curried = iso curry uncurry