choosing from Control.Lens.Lens

gistfile1.hs

{-# LANGUAGE TemplateHaskell #-}

import Control.Lens
import Data.Tree

ps :: Show a => a -> IO ()
ps = putStrLn . show

data Person = Person {
        _name :: String,
        _years :: Int    
    }        
$(makeLenses ''Person)

data Dog = Dog {
        _dogName :: String,
        _dogYears :: Int    
    }        
$(makeLenses ''Dog)

main = do
    let myfold = choosing folded folded
    ps $ Left [1,2,3,4]^..myfold
    ps $ Right (Node 3 [])^..myfold
    
    let mylens = choosing years dogYears
    ps $ Left (Person "Wanda" 34)^.mylens
    ps $ Right (Dog "Spotty" 7)^.mylens

    let mylens' = choosing name dogName
    traverseOf_ mylens' putStrLn $ Left (Person "Wanda" 34)
    traverseOf_ mylens' putStrLn $ Right (Dog "Spotty" 7)

    return ()