Foundation in this build does include NSString but there's lots a caveats associated with it. It's not bridged to String as it is on OS X yet and I suspect (but haven't verified yet,) that most other Foundation objects that are bridged on OS X are not yet bridged on Linux. So casting as in the example below will fail:
While on OS X, it will do as expected:
In order for the Linux version of Swift-repl to recognize Foundation, it needs to be invoked as follows:
This tells Swift that you're using Foundation and to link (-l) with the Foundation shared library. However, this is not needed on OS X.
Feel free to contact me if you have any questions,