The same thing in Haskell:

    cycle seq = circular where circular = seq ++ circular

(or if you want to really golf it)

    cycle = fix . (++)

Ok, to be fair the Scala code is a bit more generic as it works for any abstract sequence, but still, Scala's syntax is awfully heavy compared to Haskell.

That's one reason I still prefer Haskell even though Scala is easier to sneak into enterprise projects thanks to JVM. Not to mention that Haskell gives stronger static guarantees and has a more sophisticated type inference system.