Many programming languages allow code in foreign languages to be linked into the applicationexecutable. In Erlang, we don’t allow this for reasons of safety.1 If we were to link an externalprogram into the Erlang executable, then a mistake in the external program could easily crash theErlang system. For this reason, all foreign language code must be run outside the Erlang system inan external operating system process. The Erlang system and the external process communicate througha byte stream.