TITLE: Haskell Update Record Trick

• Update different fields in one line

module Main where
import AronModule
import Data.IORef
import Control.Lens hiding (pre, re)

data MyRec = MyRec {a_ :: Int, b_ :: Int} deriving (Eq, Show)

main = do
       let r = MyRec {a_ = 3, b_ =  4}
       refR <- newIORef r
       modifyIORef refR (\s  -> let s' = s{a_ = 100} in s'{a_ = a_ s' + 100})
       rt <- readIORef refR
       print $ show rt