1 files changed, 18 insertions, 0 deletions
diff --git a/users/Profpatsch/whatcd-resolver/src/Optional.hs b/users/Profpatsch/whatcd-resolver/src/Optional.hs
new file mode 100644
index 0000000000..9791c84970
--- /dev/null
+++ b/users/Profpatsch/whatcd-resolver/src/Optional.hs
@@ -0,0 +1,18 @@
+module Optional where
+
+import GHC.Records (getField)
+import MyPrelude
+
+newtype Optional a = OptionalInternal (Maybe a)
+  deriving newtype (Functor)
+
+mkOptional :: a -> Optional a
+mkOptional defaultValue = OptionalInternal $ Just defaultValue
+
+defaults :: Optional a
+defaults = OptionalInternal Nothing
+
+instance HasField "withDefault" (Optional a) (a -> a) where
+  getField (OptionalInternal m) defaultValue = case m of
+    Nothing -> defaultValue
+    Just a -> a