1 files changed, 61 insertions, 0 deletions
diff --git a/lib/ur/option.ur b/lib/ur/option.ur
new file mode 100644
index 0000000..baa0846
--- /dev/null
+++ b/lib/ur/option.ur
@@ -0,0 +1,61 @@
+datatype t = datatype Basis.option
+
+val monad = mkMonad {Return = @@Some,
+                     Bind = fn [a] [b] (m1 : t a) (m2 : a -> t b) =>
+                               case m1 of
+                                   None => None
+                                 | Some v => m2 v}
+
+fun eq [a] (_ : eq a) =
+    mkEq (fn x y =>
+             case (x, y) of
+                 (None, None) => True
+               | (Some x, Some y) => x = y
+               | _ => False)
+
+fun ord [a] (_ : ord a) =
+    mkOrd {Lt = fn x y =>
+                   case (x, y) of
+                       (None, Some _) => True
+                     | (Some x, Some y) => x < y
+                     | _ => False,
+           Le = fn x y =>
+                   case (x, y) of
+                       (None, _) => True
+                     | (Some x, Some y) => x <= y
+                     | _ => False}
+
+fun isNone [a] x =
+    case x of
+        None => True
+      | Some _ => False
+
+fun isSome [a] x =
+    case x of
+        None => False
+      | Some _ => True
+
+fun mp [a] [b] f x =
+    case x of
+        None => None
+      | Some y => Some (f y)
+
+fun app [m] [a] (_ : monad m) (f : a -> m {}) x =
+    case x of
+        None => return ()
+      | Some y => f y
+
+fun bind [a] [b] f x =
+    case x of
+        None => None
+      | Some y => f y
+
+fun get [a] (x : a) (o : option a) =
+    case o of
+        None => x
+      | Some v => v
+
+fun unsafeGet [a] (o : option a) =
+    case o of
+        None   => error <xml>Option.unsafeGet: encountered None</xml>
+      | Some v => v