Add ^?! and ^@?! (#53)

* Add ^?! and ^@?!

* User fromMaybe' to avoid crashed caused by strict execution

* Add a test for ^?!

* Use unwrap as runFirst doesn't exist

* Add forgotten import

* Use Tuple instead of KV. Better error messages

* Forgot to replace a KV. I iz coding too late!

* Add unsafePartial call

Author: Ben Ford

src/Data/Lens/Prism/Partial.purs

@@ -0,0 +1,36 @@
+module Data.Lens.Prism.Partial
+  ( unsafeViewPrism, (^?!)
+  , unsafeIndexedFold, (^@?!)
+  )
+  where
+
+import Prelude
+
+import Data.Lens.Fold (Fold, ifoldMapOf, previewOn)
+import Data.Lens.Types (IndexedFold)
+import Data.Maybe (fromMaybe', Maybe(..))
+import Data.Maybe.First (First(..))
+import Data.Tuple(Tuple(..))
+import Data.Newtype (unwrap)
+import Partial.Unsafe (unsafeCrashWith)
+
+unsafeViewPrism :: forall s t a b. Partial => s -> Fold (First a) s t a b -> a
+unsafeViewPrism s l = fromMaybe' (crash "unsafeViewPrism: Empty fold") $ previewOn s l
+
+infixl 8 unsafeViewPrism as ^?!
+
+
+unsafeIndexedFold
+  :: forall i s t a b. Partial
+  => s
+  -> IndexedFold ((First (Tuple i a))) i s t a b
+  -> (Tuple i a)
+unsafeIndexedFold s l = fromMaybe' (crash "unsafeIndexedFold: empty Fold")
+                          $ unwrap
+                           $ ifoldMapOf l (\i a -> First $ Just (Tuple i a)) s
+
+infixl 8 unsafeIndexedFold as ^@?!
+
+
+crash :: forall a. String -> Unit -> a
+crash msg _ = unsafeCrashWith msg

test/Main.purs

@@ -7,10 +7,12 @@ import Data.Lens.Index (ix)
 import Data.Lens.Setter (iover)
 import Data.Lens.Lens (ilens, IndexedLens, cloneIndexedLens)
 import Data.Lens.Fold ((^?))
+import Data.Lens.Prism.Partial ((^?!))
 import Data.Lens.Zoom (Traversal, Traversal', Lens, Lens', zoom)
 import Data.Tuple  (Tuple(..))
 import Data.Maybe  (Maybe(..))
 import Data.Either (Either(..))
+import Partial.Unsafe (unsafePartial)
 
 import Control.Monad.Eff (Eff)
 import Control.Monad.Eff.Console (CONSOLE, logShow)
@@ -50,6 +52,7 @@ _1bars :: Traversal' Bar Int
 _1bars = _0Justbar <<< _Left <<< bar <<< ix 1
 
 
+
 -- Tests state using zoom
 stateTest :: Tuple Int String
 stateTest = evalState go (Tuple 4 ["Foo", "Bar"]) where
@@ -66,5 +69,6 @@ main :: forall e. Eff (console :: CONSOLE | e) Unit
 main = do
   logShow $ view bars doc
   logShow $ doc2 ^? _1bars
+  logShow $ unsafePartial $ doc2 ^?! _1bars
   logShow stateTest
   logShow cloneTest