From be024166e5efc6433f77ad439ec7b492cba9ce5a Mon Sep 17 00:00:00 2001
From: Jean-Baptiste Musso <jeanbaptiste@tcmlabs.fr>
Date: Thu, 7 Nov 2019 11:59:15 +0100
Subject: [PATCH] Provide example on using Newtype and Maybe Newtype

---
 examples/Newtypes.purs | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 examples/Newtypes.purs

diff --git a/examples/Newtypes.purs b/examples/Newtypes.purs
new file mode 100644
index 0000000..2435c00
--- /dev/null
+++ b/examples/Newtypes.purs
@@ -0,0 +1,37 @@
+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": "a@b.org", "bar": null, "baz": "c@d.net" }"""