feat: monad instance, some classfile constant-pool parsing

src/Language/Java/Classfile/Extract.hs

@@ -29,6 +29,14 @@ instance Applicative Extract where
       Fail -> Fail
     Fail -> Fail
 
+instance Monad Extract where
+  (>>=) :: Extract a -> (a -> Extract b) -> Extract b
+  (>>=) (Extract computeA) f = Extract $ \ input -> case computeA input of
+    Done rest a -> let
+      (Extract computeB) = f a
+      in computeB rest
+    Fail -> Fail
+
 instance Alternative Extract where
   empty :: Extract a
   empty = Extract $ const Fail