Generalise LHS of (!)

Author: garyb

examples/Nested.purs

@@ -7,7 +7,7 @@ import Control.Monad.Eff.Console (CONSOLE, logShow)
 import Control.Monad.Except (runExcept)
 
 import Data.Foreign (F, Foreign, readNumber, readString)
-import Data.Foreign.Index ((!), (!!))
+import Data.Foreign.Index ((!))
 
 import Example.Util.Value (foreignValue)
 
@@ -28,8 +28,8 @@ instance showBaz :: Show Baz where
 
 readFoo :: Foreign -> F Foo
 readFoo value = do
-  s <- value ! "foo" !! "bar" >>= readString
-  n <- value ! "foo" !! "baz" >>= readNumber
+  s <- value ! "foo" ! "bar" >>= readString
+  n <- value ! "foo" ! "baz" >>= readNumber
   pure $ Foo (Bar s) (Baz n)
 
 main :: Eff (console :: CONSOLE) Unit

src/Data/Foreign/Index.purs

@@ -3,35 +3,38 @@
 
 module Data.Foreign.Index
   ( class Index
+  , class Indexable
   , readProp
   , readIndex
   , ix, (!)
-  , ixKleisli, (!!)
+  , index
   , hasProperty
   , hasOwnProperty
   , errorAt
   ) where
 
 import Prelude
 
+import Control.Monad.Except.Trans (ExceptT)
+
 import Data.Foreign (Foreign, F, ForeignError(..), typeOf, isUndefined, isNull, fail)
 import Data.Function.Uncurried (Fn2, runFn2, Fn4, runFn4)
+import Data.Identity (Identity)
+import Data.List.NonEmpty (NonEmptyList)
 
 -- | This type class identifies types that act like _property indices_.
 -- |
 -- | The canonical instances are for `String`s and `Int`s.
 class Index i where
-  ix :: Foreign -> i -> F Foreign
+  index :: Foreign -> i -> F Foreign
   hasProperty :: i -> Foreign -> Boolean
   hasOwnProperty :: i -> Foreign -> Boolean
   errorAt :: i -> ForeignError -> ForeignError
 
-infixl 9 ix as !
-
-ixKleisli :: forall i. Index i => F Foreign -> i -> F Foreign
-ixKleisli f i = f >>= (_ ! i)
+class Indexable a where
+  ix :: forall i. Index i => a -> i -> F Foreign
 
-infixl 9 ixKleisli as !!
+infixl 9 ix as !
 
 foreign import unsafeReadPropImpl :: forall r k. Fn4 r (Foreign -> r) k Foreign r
 
@@ -64,13 +67,19 @@ hasPropertyImpl p value | typeOf value == "object" || typeOf value == "function"
 hasPropertyImpl _ value = false
 
 instance indexString :: Index String where
-  ix = flip readProp
+  index = flip readProp
   hasProperty = hasPropertyImpl
   hasOwnProperty = hasOwnPropertyImpl
   errorAt = ErrorAtProperty
 
 instance indexInt :: Index Int where
-  ix = flip readIndex
+  index = flip readIndex
   hasProperty = hasPropertyImpl
   hasOwnProperty = hasOwnPropertyImpl
   errorAt = ErrorAtIndex
+
+instance indexableForeign :: Indexable Foreign where
+  ix = index
+
+instance indexableExceptT :: Indexable (ExceptT (NonEmptyList ForeignError) Identity Foreign) where
+  ix f i = flip index i =<< f