lens.hs

{-# LANGUAGE TemplateHaskell, Rank2Types #-}
import Prelude hiding ((.), id)
import Control.Category
import Control.Lens
import Control.Lens.TH

type Register = Int

data Machine = Machine { _ax :: Register, _bx :: Register } deriving Show
data SMPMachine = SMP { _cpu0 :: Machine, _cpu1 :: Machine } deriving Show

makeLenses ''Machine
makeLenses ''SMPMachine

mov :: Lens' m r -> Lens' m r -> m -> m
mov from to m = set to (m ^. from) m

main = do
    let m = Machine 42 69
    putStrLn $ show m
    let m' = mov ax bx m
    putStrLn $ show m'

    let s = SMP (Machine 22 0) (Machine 99 11)
    putStrLn $ show s
    let s' = mov (cpu0.ax) (cpu1.bx) s
    putStrLn $ show s'