我有这样的代码来转换一些数据：

newtype XXX = XXX
  { xxx :: [ Text ]
  } deriving (Eq, Show)

oldToNew
  :: [XXX] -> [(Int, [(Int, Text)])]
  -> [[(Int, Int, Text)]]
oldToNew xs old                = map    go1          xs
 where
  go1 (XXX eqs)                = foldr  go2      []  eqs
  go2 l                    acc = foldr (go3 l)   acc old
  go3 l (i, w)             acc = foldr (go4 i l) acc w
  go4 idx1 label1 (idx2, label2) acc =
    if label1 == label2
    then (idx1, idx2, label2):acc
    else acc

字符串
注意两件事：
1.它将一个累加器（最初是空的）穿过所有折叠，
1.每个折叠从前一个折叠中拾取一个参数传递到下一个“go”
如何使用控制透镜和/或光学来完成上述操作。
测试用例：

oldToNewSpec :: Spec
oldToNewSpec  =
  it "oldToNew" $
    oldToNew [ XXX ["this", "that", "also"]
             , XXX ["here", "there"] ]

             [ (0, [(4, "this")])
             , (0, [(1, "here")])
             , (1, [(5, "that")])
             , (2, [(2, "also")])
             , (2, [(3, "there")]) ]
    `shouldBe`
    [ [(0,4,"this"),(1,5,"that"),(2,2,"also")]
    , [(0,1,"here"),(2,3,"there")] ]

型