authors_books_definitions.hs

module Library where

data Author = 
  Author { 
    name  :: String, 
    books :: [Book]   
  } deriving (Show)

data Book = 
  Book { 
    title :: String, 
    authors :: [Author] 
  } deriving (Show)

createAuthor a bs = let books = map (`createBook` [a]) bs
                     in Author a books

createBook b as = let authors = map (`createAuthor` [b]) as
                   in Book b authors