The only item of index satisfying (> 2) in the list things is (A 3).

Li-yao


On 03/13/2018 02:44 AM, Cody Goodman wrote:

Hello,

I'm trying to insert a new elemnt into a list after a given index and increment the orderId accordingly with the lens library.

I'm a bit confused at why this code isn't working:

```
import Control.Lens

data A = A { _customOrderId :: Int } deriving Show

things = [ A {_customOrderId = 0}
          , A {_customOrderId = 1}
          , A {_customOrderId = 2}
          , A {_customOrderId = 3}
          ]

main = print $ things & ( (_drop 2 %~ ((A 22)<|)) . ((traversed . indices (> 2) . customerOrderIdLens) %~ (+ 1))  )
```
The first portion works to insert where desired, but the second portion `((traversed . indices (> 2) . customerOrderIdLens) %~ (+ 1))` only increments the order id in indices 4.

Any idea why this is happening?

Thanks,

Cody Goodman



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