Provide an example of using Newtype and Maybe Newtype

examples/Newtypes.purs

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+module Example.Newtypes where
+
+import Prelude
+import Control.Monad.Except (runExcept)
+import Data.Maybe (Maybe)
+import Data.Traversable (traverse)
+import Effect (Effect)
+import Effect.Console (logShow)
+import Example.Util.Value (foreignValue)
+import Foreign (F, Foreign, readNullOrUndefined, readString)
+import Foreign.Index ((!))
+
+newtype Email
+  = Email String
+
+derive newtype instance showEmail :: Show Email
+
+type SomeObject
+  = { foo :: String
+    , bar :: Maybe String
+    , baz :: Email
+    , duh :: Maybe Email
+    }
+
+readObject :: Foreign -> F SomeObject
+readObject value = do
+  foo <- value ! "foo" >>= readString
+  bar <- value ! "bar" >>= readNullOrUndefined >>= traverse readString
+  baz <- value ! "baz" >>= readString <#> Email
+  duh <- value ! "duh" >>= readNullOrUndefined >>= traverse readString <#> map Email
+  pure { foo, bar, baz, duh }
+
+main :: Effect Unit
+main = do
+  logShow $ runExcept
+    $ readObject
+    =<< foreignValue """{ "foo": "[email protected]", "bar": null, "baz": "[email protected]" }"""