add < instance for Maybe

src/libraries/OS-Independent/Data/Maybe.dcl

@@ -5,7 +5,7 @@ definition module Data.Maybe
 
 import StdMaybe 
 
-from StdOverloaded import class ==(..)
+from StdOverloaded import class ==
 from Data.Functor import class Functor
 from Control.Applicative import class pure, class <*>, class Applicative, class *>, class <*, class Alternative
 from Control.Monad import class Monad, class MonadPlus

src/libraries/OS-Independent/Data/Maybe/Ord.dcl

+definition module Data.Maybe.Ord
+
+/**
+ * This contains a possible `<` and with this an `Ord` instance of the `Maybe` type.
+ * As there is no natural order and therefore an arbitrary choice is made,
+ * the instances is provided in a separate module. This makes is easier to use another ordering.
+ */
+
+from StdOverloaded import class <
+from Data.Maybe    import :: Maybe
+
+instance < (Maybe a) | < a

src/libraries/OS-Independent/Data/Maybe/Ord.icl

+implementation module Data.Maybe.Ord
+
+import StdEnv, Data.Maybe
+
+instance < (Maybe a) | < a where 
+	< Nothing   Nothing   = False 
+	< Nothing   _         = True 
+	< (Just a1) (Just a2) = a1 < a2
+	< _         _         = False

tests/linux64/test.icl

@@ -123,6 +123,7 @@ import qualified Data.Map
 import qualified Data.MapCollection
 import qualified Data.Matrix
 import qualified Data.Maybe
+import qualified Data.Maybe.Ord
 import qualified Data.Monoid
 import qualified Data.NGramIndex
 import qualified Data.OrdList