Erlang ( ) is a general-purpose, concurrent, garbage-collected programming language and runtime system. The sequential subset of Erlang is almost a functional language (excluding certain built-in functions (BIFs) such as those manipulating the process dictionary), with eager evaluation, single assignment, and dynamic typing. It was originally designed by Ericsson to support distributed, fault-tolerant, soft real-time, highly available, non-stop applications. It supports hot swapping, thus code can be changed without stopping a system.