### Composing relations (for LTS-9) Copy the following to "helloworld.hs" for LTS-9: {% highlight haskell %} import Database.Relational.Query import Data.Int (Int32) hello :: Relation () (Int32, String) hello = relation $ return (value 0 >< value "Hello") world :: Relation () (Int32, String) world = relation $ return (value 0 >< value "World!") helloWorld :: Relation () (Int32, String, String) helloWorld = relation $ do h <- query hello w <- query world on $ h ! fst' .=. w ! fst' return $ (,,) |$| h ! fst' |*| h ! snd' |*| w ! snd' main :: IO () main = putStrLn $ show helloWorld ++ ";" {% endhighlight %}