feat[FlagMask]: default signature with generic ofMask

src/Language/Java/Classfile/Flags.hs

@@ -6,10 +6,11 @@
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE UndecidableInstances #-}
 {-# LANGUAGE TypeFamilies #-}
-module Language.Java.Classfile.Flags (Flags(..), FlagMask(..)) where
+{-# LANGUAGE DefaultSignatures #-}
+module Language.Java.Classfile.Flags (Flags(..), FlagMask(..), containsFlag) where
 
 
-import Data.Bits (Bits((.&.)))
+import Data.Bits (Bits((.&.), zeroBits))
 import Data.Enum.Util (enumerate)
 import Data.Set (Set)
 
@@ -18,6 +19,8 @@ import qualified Data.Set as Set
 import Language.Java.Classfile.Extract (Extract)
 import Language.Java.Classfile.Extractable (Extractable (extract))
 import Data.Kind (Type)
+import Control.Arrow ((>>>))
+import qualified Data.List as List
 
 -- | Using the 'FlagMask' instance of the type parameter, this will extract all the flags whose mask produced a non-zero value using '.&.'
 
@@ -39,3 +42,13 @@ class FlagMask a where
   type FlagType a :: Type
   maskOf :: a -> FlagType a
 
+  ofMask :: FlagType a -> Set a
+
+  default ofMask :: (Enum a, Bounded a, Ord a, Bits (FlagType a)) => FlagType a -> Set a
+  ofMask mask = List.filter (containsFlag mask)
+    >>> Set.fromList
+    $ enumerate @a
+
+containsFlag :: (Bits (FlagType a), FlagMask a) => FlagType a -> a -> Bool
+containsFlag mask flag = mask .&. maskOf flag /= zeroBits
+