diff --git a/src/Database/IndexedDB/Class.purs b/src/Database/IndexedDB/Class.purs
new file mode 100644
index 0000000..4844da4
--- /dev/null
+++ b/src/Database/IndexedDB/Class.purs
@@ -0,0 +1,13 @@
+-- | Opaque typeclass definitions for easy reuse of functions over
+-- | imported foreign types.
+module Database.IndexedDB.Class where
+
+
+-- | Cursor objects implement the IDBCursor interface.
+-- | There is only ever one IDBCursor instance representing a given cursor.
+-- | There is no limit on how many cursors can be used at the same time.
+class IDBCursor cursor
+
+-- | A concrete cursor not only shares IDBCursor properties, but also some
+-- | specific attributes (see KeyCursor or CursorWithValue).
+class (IDBCursor cursor) <= IDBConcreteCursor cursor
diff --git a/src/Database/IndexedDB/Core.js b/src/Database/IndexedDB/Core.js
index 828636e..0cf0fa5 100644
--- a/src/Database/IndexedDB/Core.js
+++ b/src/Database/IndexedDB/Core.js
@@ -3,14 +3,6 @@ const toArray = function toArray(xs) {
 };
 
 
-exports._showCursor = function _showCursor(cursor) {
-    return '(IDBCursor ' +
-        '{ direction: ' + cursor.direction +
-        ', key: ' + cursor.key +
-        ', primaryKey: ' + cursor.primaryKey +
-        ' })';
-};
-
 exports._showDatabase = function _showDatabase(db) {
     return '(IDBDatabase ' +
         '{ name: ' + db.name +
diff --git a/src/Database/IndexedDB/Core.purs b/src/Database/IndexedDB/Core.purs
index 6df4e82..b42008d 100644
--- a/src/Database/IndexedDB/Core.purs
+++ b/src/Database/IndexedDB/Core.purs
@@ -9,17 +9,14 @@
 
 module Database.IndexedDB.Core
   ( IDB
-  , CursorDirection(..)
   , CursorSource(..)
   , Database
   , Index
-  , KeyCursor
   , KeyRange
   , KeyPath
   , ObjectStore
   , Transaction
   , TransactionMode(..)
-  , ValueCursor
   , module Database.IndexedDB.IDBKey
   ) where
 
@@ -35,18 +32,6 @@ import Database.IndexedDB.IDBKey
 foreign import data IDB :: Effect
 
 
--- | A cursor has a direction that determines whether it moves in monotonically
--- | increasing or decreasing order of the record keys when iterated, and if it
--- | skips duplicated values when iterating indexes.
--- | The direction of a cursor also determines if the cursor initial position is at
--- | the start of its source or at its end.
-data CursorDirection
-  = Next
-  | NextUnique
-  | Prev
-  | PrevUnique
-
-
 -- | If the source of a cursor is an object store, the effective object store of
 -- | the cursor is that object store and the effective key of the cursor is the
 -- | cursor’s position. If the source of a cursor is an index, the effective object
@@ -86,11 +71,6 @@ foreign import data Database :: Type
 foreign import data Index :: Type
 
 
--- | A cursor is used to iterate over a range of records in an index or an object store
--- | in a specific direction. A KeyCursor doesn't hold any value.
-foreign import data KeyCursor :: Type
-
-
 -- | A key range is a continuous interval over some data type used for keys.
 foreign import data KeyRange :: Type
 
@@ -104,20 +84,6 @@ foreign import data ObjectStore :: Type
 foreign import data Transaction :: Type
 
 
--- | A cursor is used to iterate over a range of records in an index or an object store
--- | in a specific direction. A ValueCursor also holds the value corresponding to matching key.
-foreign import data ValueCursor :: Type
-
-
-foreign import _showCursor :: forall cursor. cursor -> String
-instance showKeyCursor :: Show KeyCursor where
-  show = _showCursor
-
-
-instance showValueCursor :: Show ValueCursor where
-  show = _showCursor
-
-
 foreign import _showDatabase
   :: Database
   -> String
@@ -153,15 +119,6 @@ instance showTransaction :: Show Transaction where
   show = _showTransaction
 
 
-instance showCursorDirection :: Show CursorDirection where
-  show x =
-    case x of
-      Next       -> "next"
-      NextUnique -> "nextunique"
-      Prev       -> "prev"
-      PrevUnique -> "prevunique"
-
-
 instance showTransactionMode :: Show TransactionMode where
   show x =
     case x of
@@ -170,16 +127,6 @@ instance showTransactionMode :: Show TransactionMode where
       VersionChange -> "versionchange"
 
 
-instance readCursorDirection :: Read CursorDirection where
-  read s =
-    case s of
-      "next"       -> Just Next
-      "nextunique" -> Just NextUnique
-      "prev"       -> Just Prev
-      "prevunique" -> Just PrevUnique
-      _            -> Nothing
-
-
 instance readTransactionMode :: Read TransactionMode where
   read s =
     case s of
diff --git a/src/Database/IndexedDB/IDBCursor.js b/src/Database/IndexedDB/IDBCursor.js
index 8845888..1ab42da 100644
--- a/src/Database/IndexedDB/IDBCursor.js
+++ b/src/Database/IndexedDB/IDBCursor.js
@@ -11,6 +11,14 @@ const successHandler = function successHandler(cb) {
 };
 
 
+exports._showCursor = function _showCursor(cursor) {
+    return '(IDBCursor ' +
+        '{ direction: ' + cursor.direction +
+        ', key: ' + cursor.key +
+        ', primaryKey: ' + cursor.primaryKey +
+        ' })';
+};
+
 exports._advance = function _advance(cursor, count) {
     return function aff(success, error) {
         try {
diff --git a/src/Database/IndexedDB/IDBCursor.purs b/src/Database/IndexedDB/IDBCursor.purs
index 8da88de..4de6455 100644
--- a/src/Database/IndexedDB/IDBCursor.purs
+++ b/src/Database/IndexedDB/IDBCursor.purs
@@ -1,126 +1,130 @@
 -- | A cursor is used to iterate over a range of records in an index or
 -- | an object store in a specific direction.
 module Database.IndexedDB.IDBCursor
-  ( class IDBCursor, advance, continue, continuePrimaryKey, delete, update
+  -- * Cursor Manipulation
+  ( KeyCursor
+  , ValueCursor
+  , CursorDirection(..)
+  , advance
+  , continue
+  , continuePrimaryKey
+  , delete
+  , update
+
+  -- * Concrete Cursor Manipulation
   , direction
   , key
   , primaryKey
   , source
-  , direction'
-  , key'
-  , primaryKey'
-  , source'
   , value
   ) where
 
-import Prelude                            (Unit, ($), (>>>), map)
+import Prelude                            (class Show, Unit, ($), (>>>), map)
 
 import Control.Monad.Aff                  (Aff)
 import Data.Foreign                       (Foreign, toForeign, unsafeFromForeign)
 import Data.Function.Uncurried             as Fn
 import Data.Function.Uncurried            (Fn2, Fn3)
-import Data.Maybe                         (Maybe)
+import Data.Maybe                         (Maybe(..))
 import Data.Nullable                      (Nullable, toNullable)
-import Data.String.Read                   (read)
+import Data.String.Read                   (class Read, read)
 
 import Database.IndexedDB.Core
 import Database.IndexedDB.IDBKey.Internal (class IDBKey, Key(..), toKey, extractForeign)
+import Database.IndexedDB.Class           (class IDBCursor, class IDBConcreteCursor)
+
+
+--------------------
+-- TYPES
+--
+
+-- | A cursor is used to iterate over a range of records in an index or an object store
+-- | in a specific direction. A KeyCursor doesn't hold any value.
+foreign import data KeyCursor :: Type
+
+
+-- | A cursor is used to iterate over a range of records in an index or an object store
+-- | in a specific direction. A ValueCursor also holds the value corresponding to matching key.
+foreign import data ValueCursor :: Type
+
+
+-- | A cursor has a direction that determines whether it moves in monotonically
+-- | increasing or decreasing order of the record keys when iterated, and if it
+-- | skips duplicated values when iterating indexes.
+-- | The direction of a cursor also determines if the cursor initial position is at
+-- | the start of its source or at its end.
+data CursorDirection
+  = Next
+  | NextUnique
+  | Prev
+  | PrevUnique
 
 
 --------------------
 -- INTERFACES
 --
--- | Cursor objects implement the IDBCursor interface.
--- | There is only ever one IDBCursor instance representing a given cursor.
--- | There is no limit on how many cursors can be used at the same time.
-class IDBCursor cursor where
-    -- | Advances the cursor through the next count records in range.
-    advance
-        :: forall e
-        .  cursor
-        -> Int
-        -> Aff (idb :: IDB | e) Unit
 
-    -- | Advances the cursor to the next record in range matching or after key.
-    continue
-        :: forall e k. (IDBKey k)
-        => cursor
-        -> Maybe k
-        -> Aff (idb :: IDB | e) Unit
+-- | Advances the cursor through the next count records in range.
+advance
+    :: forall e cursor. (IDBCursor cursor)
+    => cursor
+    -> Int
+    -> Aff (idb :: IDB | e) Unit
+advance =
+  Fn.runFn2 _advance
 
-    -- | Advances the cursor to the next record in range matching or after key and primaryKey. Throws an "InvalidAccessError" DOMException if the source is not an index.
-    continuePrimaryKey
-        :: forall e k. (IDBKey k)
-        => cursor
-        -> k
-        -> k
-        -> Aff (idb :: IDB | e) Unit
 
-    -- | Delete the record pointed at by the cursor with a new value.
-    delete
-        :: forall e
-        .  cursor
-        -> Aff (idb :: IDB | e) Unit
+-- | Advances the cursor to the next record in range matching or after key.
+continue
+    :: forall e k cursor. (IDBKey k) => (IDBCursor cursor)
+    => cursor
+    -> Maybe k
+    -> Aff (idb :: IDB | e) Unit
+continue c mk =
+  Fn.runFn2 _continue c (toNullable $ map (toKey >>> extractForeign) mk)
 
-    -- | Update the record pointed at by the cursor with a new value.
-    -- |
-    -- | Throws a "DataError" DOMException if the effective object store uses
-    -- | in-line keys and the key would have changed.
-    update
-        :: forall val e
-        .  cursor
-        -> val
-        -> Aff (idb :: IDB | e) Key
+
+-- | Advances the cursor to the next record in range matching or after key and primaryKey. Throws an "InvalidAccessError" DOMException if the source is not an index.
+continuePrimaryKey
+    :: forall e k cursor. (IDBKey k) => (IDBCursor cursor)
+    => cursor
+    -> k
+    -> k
+    -> Aff (idb :: IDB | e) Unit
+continuePrimaryKey c k1 k2 =
+  Fn.runFn3 _continuePrimaryKey c (extractForeign $ toKey k1) (extractForeign $ toKey k2)
+
+
+-- | Delete the record pointed at by the cursor with a new value.
+delete
+    :: forall e cursor. (IDBCursor cursor)
+    => cursor
+    -> Aff (idb :: IDB | e) Unit
+delete =
+  _delete
+
+
+-- | Update the record pointed at by the cursor with a new value.
+-- |
+-- | Throws a "DataError" DOMException if the effective object store uses
+-- | in-line keys and the key would have changed.
+update
+    :: forall val e cursor. (IDBCursor cursor)
+    => cursor
+    -> val
+    -> Aff (idb :: IDB | e) Key
+update c =
+  toForeign >>> Fn.runFn2 _update c >>> map Key
 
 
 --------------------
 -- ATTRIBUTES
 --
--- | Returns the direction (Next|NextUnique|Prev|PrevUnique) of the cursor.
-direction'
-  :: KeyCursor
-  -> CursorDirection
-direction' =
-  Fn.runFn2 _direction (read >>> toNullable)
-
-
--- | Returns the key of the cursor. Throws a "InvalidStateError" DOMException
--- | if the cursor is advancing or is finished.
-key'
-  :: forall e
-  .  KeyCursor
-  -> Aff (idb :: IDB | e) Key
-key' =
-  _key >>> map Key
-
-
--- | Returns the effective key of the cursor. Throws a "InvalidStateError" DOMException
--- | if the cursor is advancing or is finished.
-primaryKey'
-  :: forall e
-  .  KeyCursor
-  -> Aff (idb :: IDB | e) Key
-primaryKey' =
-  _primaryKey >>> map Key
-
-
--- | Returns the IDBObjectStore or IDBIndex the cursor was opened from.
-source'
-  :: KeyCursor
-  -> CursorSource
-source' =
-  Fn.runFn3 _source ObjectStore Index
-
-
--- NOTE: Polymorphism not used here cause *we want* those methods to be distincs for
--- the concrete types mostly for consistency with the Database.IndexedDB.IDBIndex module
--- where the IDBIndex interfaces is shared by Index and ObjectStore, but attributes of
--- respective concrete types aren't shared.
-
 
 -- | Returns the direction (Next|NextUnique|Prev|PrevUnique) of the cursor.
 direction
-  :: ValueCursor
+  :: forall cursor. (IDBConcreteCursor cursor)
+  => cursor
   -> CursorDirection
 direction =
   Fn.runFn2 _direction (read >>> toNullable)
@@ -129,8 +133,8 @@ direction =
 -- | Returns the key of the cursor. Throws a "InvalidStateError" DOMException
 -- | if the cursor is advancing or is finished.
 key
-  :: forall e
-  .  ValueCursor
+  :: forall e cursor. (IDBConcreteCursor cursor)
+  => cursor
   -> Aff (idb :: IDB | e) Key
 key =
   _key >>> map Key
@@ -139,8 +143,8 @@ key =
 -- | Returns the effective key of the cursor. Throws a "InvalidStateError" DOMException
 -- | if the cursor is advancing or is finished.
 primaryKey
-  :: forall e
-  .  ValueCursor
+  :: forall e cursor. (IDBConcreteCursor cursor)
+  => cursor
   -> Aff (idb :: IDB | e) Key
 primaryKey =
   _primaryKey >>> map Key
@@ -148,7 +152,8 @@ primaryKey =
 
 -- | Returns the IDBObjectStore or IDBIndex the cursor was opened from.
 source
-  :: ValueCursor
+  :: forall cursor. (IDBConcreteCursor cursor)
+  => cursor
   -> CursorSource
 source =
   Fn.runFn3 _source ObjectStore Index
@@ -165,25 +170,57 @@ value =
 --------------------
 -- INSTANCES
 --
-instance keyCursorKeyCursor :: IDBCursor KeyCursor where
-  advance                    = Fn.runFn2 _advance
-  continue c mk              = Fn.runFn2 _continue c (toNullable $ map (toKey >>> extractForeign) mk)
-  continuePrimaryKey c k1 k2 = Fn.runFn3 _continuePrimaryKey c (extractForeign $ toKey k1) (extractForeign $ toKey k2)
-  delete                     = _delete
-  update c                   = toForeign >>> Fn.runFn2 _update c >>> map Key
+
+instance idbCursorKeyCursor :: IDBCursor KeyCursor
 
 
-instance valueCursorKeyCursor :: IDBCursor ValueCursor where
-  advance                    = Fn.runFn2 _advance
-  continue c mk              = Fn.runFn2 _continue c (toNullable $ map (toKey >>> extractForeign) mk)
-  continuePrimaryKey c k1 k2 = Fn.runFn3 _continuePrimaryKey c (extractForeign $ toKey k1) (extractForeign $ toKey k2)
-  delete                     = _delete
-  update c                   = toForeign >>> Fn.runFn2 _update c >>> map Key
+instance idbCursorValueCursor :: IDBCursor ValueCursor
+
+
+instance idbConcreteCursorKeyCursor :: IDBConcreteCursor KeyCursor
+
+
+instance idbConcreteCursorValueCursor :: IDBConcreteCursor ValueCursor
+
+
+instance showKeyCursor :: Show KeyCursor where
+  show = _showCursor
+
+
+instance showValueCursor :: Show ValueCursor where
+  show = _showCursor
+
+
+instance showCursorDirection :: Show CursorDirection where
+  show x =
+    case x of
+      Next       -> "next"
+      NextUnique -> "nextunique"
+      Prev       -> "prev"
+      PrevUnique -> "prevunique"
+
+
+
+instance readCursorDirection :: Read CursorDirection where
+  read s =
+    case s of
+      "next"       -> Just Next
+      "nextunique" -> Just NextUnique
+      "prev"       -> Just Prev
+      "prevunique" -> Just PrevUnique
+      _            -> Nothing
 
 
 --------------------
 -- FFI
 --
+
+foreign import _showCursor
+  :: forall cursor
+  .  cursor
+  -> String
+
+
 foreign import _advance
   :: forall cursor e
   .  Fn2 cursor Int (Aff (idb :: IDB | e) Unit)
diff --git a/src/Database/IndexedDB/IDBIndex/Internal.purs b/src/Database/IndexedDB/IDBIndex/Internal.purs
index 9698a16..864701c 100644
--- a/src/Database/IndexedDB/IDBIndex/Internal.purs
+++ b/src/Database/IndexedDB/IDBIndex/Internal.purs
@@ -13,7 +13,8 @@ import Data.Function.Uncurried            (Fn2, Fn3, Fn4)
 import Data.Maybe                         (Maybe)
 import Data.Nullable                      (Nullable, toMaybe, toNullable)
 
-import Database.IndexedDB.Core            (IDB, CursorDirection, Index, Key, KeyCursor, KeyRange, KeyPath, ObjectStore, ValueCursor)
+import Database.IndexedDB.Core            (IDB, Index, Key, KeyRange, KeyPath, ObjectStore)
+import Database.IndexedDB.IDBCursor       (CursorDirection, KeyCursor, ValueCursor)
 import Database.IndexedDB.IDBKey.Internal (class IDBKey, Key(..))