Parser combinators are a clean and powerful abstraction which can provide reasonably efficient means of parsing a grammar into a form which the programmer desires. They remain close to the domain of grammars whilst at the same time offering enormous flexibility. In Haskell, the Parsec library is a prime example of such a library. However, a direct translation to Scala proves to be unbearably slow. This paper describes the semantics and design of a new library, called Parsley, which retains a close resemblance to Parsec style whilst providing very competitive performance.