Erlang is a general-purpose concurrent programming language and runtime system. The sequential subset of Erlang is a functional language, with strict evaluation, single assignment, and dynamic typing. For concurrency it follows the Actor model. It was designed by Ericsson to support distributed, fault-tolerant, soft-real-time, non-stop applications. The first version was designed and implemented by Joe Armstrong in 1986. It supports hot swapping so code can be changed without stopping a system. Erlang was originally a proprietary language within Ericsson, but was released as open source in 1998. The Ericsson implementation primarily runs interpreted virtual machine code, but it also includes a native code compiler (supported on most but not all platforms), developed by the High Performance Erlang Project (HiPE) at Uppsala University.