haskell - Haskell/Persistent: 「selectList」の再利用

Question

私は Servant で API を作成しようとしていますが、次のような多くのハンドラーを作成しています。

getTableA :: Handler [ARecord]
getTableA = do
    xs <- runDB (selectList [] [])
    let records = map (\(Entity _ v) -> v) xs
    return records

getTableB :: Handler [BRecord]
getTableB = do
    xs <- runDB (selectList [] [])
    let records = map (\(Entity _ v) -> v) xs
    return records

getTableC :: Handler [CRecord]
getTableC = do
    xs <- runDB (selectList [] [])
    let records = map (\(Entity _ v) -> v) xs
    return records

等々。

もっと似たものを持てるようになりたい

getTable :: Handler [a]
getTable = do
    xs <- runDB (selectList [] [])
    let records = map (\(Entity _ v) -> v) xs
    return records

ただし、エラーが発生します

Couldn't match expected type ‘SqlBackend’
            with actual type ‘PersistEntityBackend val’
Relevant bindings include
  getAll :: Handler [val] (bound at src/Novation/Handler.hs:101:1)
In the first argument of ‘runDB’, namely ‘(selectList [] [])’
In a stmt of a 'do' block: xs <- runDB (selectList [] [])
In the expression:
  do { xs <- runDB (selectList [] []);
       let records = map (\ (Entity _ v) -> ...) xs;
       return records }

最終的にはこのようなものを手に入れることができることを願っています

server :: Server MyAPI
server = getTable :<|> getTable :<|> getTable

type MyAPI = 
         "tableA" :> Get '[JSON] [ARecord]
    :<|> "tableB" :> Get '[JSON] [BRecord]
    :<|> "tableC" :> Get '[JSON] [CRecord]

それ以外の

server :: Server MyAPI
server = getTableA :<|> getTableB :<|> getTableC