IBM has today unveiled their first public effort towards Swift, with the introduction of the IBM Swift Sandbox website. You can type lines of Swift code into the text editor on the left and then run the code on a Linux server, posting the output in the right column. This is all made possible by the fact that Swift is now open source, supporting Linux alongside iOS and OS X.
You can use the core Swift language as well as the standard library functions, so writing a formulaic mathematical problem (like the Fibonacci example above) is well within the scope of the web application. The concept is similar to the CodeRunner app from the Mac App Store, except it runs entirely off a cloud infrastructure.