PLEX (Programming Language for EXchanges) is a special-purpose, concurrent, real-time

programming language A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language. The description of a programming l ...

. The proprietary PLEX language is closely tied to the architecture of Ericsson's AXE telephone exchanges which it was designed to control. PLEX was developed by Göran Hemdahl at

Ericsson (lit. "Telephone Stock Company of LM Ericsson"), commonly known as Ericsson, is a Sweden, Swedish multinational networking and telecommunications company headquartered in Stockholm. The company sells infrastructure, software, and services in ...

in the 1970s, and it has been continuously evolving since then. PLEX was described in 2008 as "a cross between Fortran and a

macro assembler Macro (or MACRO) may refer to: Science and technology * Macroscopic, subjects visible to the eye * Macro photography, a type of close-up photography * Image macro, a picture with text superimposed * Monopole, Astrophysics and Cosmic Ray Observa ...

." The language has two variants: ''Plex-C'' used for the AXE Central Processor (CP) and ''Plex-M'' used for Extension Module Regional Processors (EMRP). Ericsson started a project in the mid-1980s to create a successor language which resulted in Erlang. According to co-creator Joe Armstrong, "Erlang was heavily influenced by PLEX and the AXE design." Erlang did not replace PLEX, but was used alongside it.

Execution model

A system is divided into separately compiled and loaded units of code called "blocks." A block waits for one or more signals sent from elsewhere in the system which triggers code execution.

Pre-compilers

Several precompilers or code generators exist, to produce

source code In computing, source code, or simply code, is any collection of code, with or without comment (computer programming), comments, written using a human-readable programming language, usually as plain text. The source code of a Computer program, p ...

in ''Plex-C'' from higher level languages or graphical models. These can generate ''Plex-C'' from: * Specification and Description Language graphical representation (SDL/GR) * ''Plex-SQL'', an extension of ''Plex-C'' with

database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases spa ...

facilities * ''High Level Plex'' (HLPLEX) another extension of ''Plex-C'' Source code in ''Plex-C'' is compiled into the assembly language ''ASA210C.'' The binary form of ''ASA210C'' is either interpreted by a combination of hardware and

microcode In processor design, microcode (μcode) is a technique that interposes a layer of computer organization between the central processing unit (CPU) hardware and the programmer-visible instruction set architecture of a computer. Microcode is a la ...

, or is compiled by a just-in-time compiler into native

machine code In computer programming, machine code is any low-level programming language, consisting of machine language instructions, which are used to control a computer's central processing unit (CPU). Each instruction causes the CPU to perform a ver ...

for a high-capacity

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...

References

Concurrent programming languages Domain-specific programming languages Ericsson Programming languages created in the 1970s {{Compu-lang-stub