type R a = { f1 :: a, f2 :: String }


type Person = { name :: String, age :: Int, friends :: [Person] }

john = { name := "John", age := 21, friends := [tim] }

tim = { name := "Tim", age := 26, friends := [john] }

ann = { name := "Ann", age := 20, friends := [john,ann] }

getFriends :: Person -> [Person]
getFriends p = p :> friends

addFriend :: Person -> Person -> Person
addFriend p friend = { friends := friend : (getFriends p) | p }

getNames :: Person -> [String]
getNames { friends = fs | _ } = map (\p -> p :> name) fs

--------------------------------------------------------------------------------

type R1 = { r2 :: R2 }
type R2 = { r1 :: R1 }

rec1 = { r2 := rec2 }
rec2 = { r1 := rec1 }

type R3 = { r3 :: TSR3 }
type TSR3 = R3