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Limbo
Paradigm	Concurrent
Designed by	Sean Dorward, Phil Winterbottom, Rob Pike
Developer	Bell Labs / Vita Nuova Holdings
First appeared	1995; 30 years ago
Typing discipline	Strong
OS	Inferno
License	GNU GPL v2, see NOTICE in limbo subfolder of the tarball
Website	www.vitanuova.com/inferno/limbo.html
Major implementations
	Dis virtual machine
Influenced by
	C, Pascal, CSP, Alef, Newsqueak
Influenced
	Stackless Python, Go, Rust

Limbo is a programming language for writing distributed systems and is the language used to write applications for the Inferno operating system. It was designed at Bell Labs by Sean Dorward, Phil Winterbottom, and Rob Pike.^[1]

The Limbo compiler generates architecture-independent object code which is then interpreted by the Dis virtual machine or compiled just before runtime to improve performance. Therefore all Limbo applications are completely portable across all Inferno platforms.

Limbo's approach to concurrency was inspired by Hoare's communicating sequential processes (CSP), as implemented and amended in Pike's earlier Newsqueak language and Winterbottom's Alef.

Language features

Limbo supports the following features:

modular programming
concurrent programming
strong type checking at compile and run-time
interprocess communication over typed channels
automatic garbage collection
simple abstract data types

Virtual machine

The Dis virtual machine that executes Limbo code is a CISC-like VM, with instructions for arithmetic, control flow, data motion, process creation, synchronizing and communicating between processes, loading modules of code, and support for higher-level data-types: strings, arrays, lists, and communication channels.^[2] It uses a hybrid of reference counting and a real-time garbage-collector for cyclic data.^[3]

Aspects of the design of Dis were inspired by the AT&T Hobbit microprocessor, as used in the original BeBox.

Examples

Limbo uses Ada-style definitions as in:

name := type value;
name0,name1 : type = value;
name2,name3 : type;
name2 = value;

Hello world

implement Command;

include "sys.m";
    sys: Sys;

include "draw.m";

include "sh.m";

init(nil: ref Draw->Context, nil: list of string)
{
    sys = load Sys Sys->PATH;
    sys->print("Hello World!\n");
}

Books

The 3rd edition of the Inferno operating system and Limbo programming language are described in the textbook Inferno Programming with Limbo ISBN 0-470-84352-7 (Chichester: John Wiley & Sons, 2003), by Phillip Stanley-Marbell. Another textbook The Inferno Programming Book: An Introduction to Programming for the Inferno Distributed System, by Martin Atkins, Charles Forsyth, Rob Pike and Howard Trickey, was started, but never released.

References

^ "Inferno Application Programming". vitanuova. vitanuova. Retrieved January 26, 2021.
^ "Dis Virtual Machine Specification". Vita Nuova. 2000. Retrieved 2 February 2015.
^ Lorenz Huelsbergen and Phil Winterbottomv (1998). "Very Concurrent Mark and Sweep Garbage Collection without Fine-Grain Synchronization" (PDF). 1998 International Symposium on Memory Management.

External links

Vita Nuova page on Limbo
A Descent into Limbo by Brian Kernighan
The Limbo Programming Language by Dennis M. Ritchie and Addendum by Vita Nuova.
Inferno Programming with Limbo by Phillip Stanley-Marbell
Threaded programming in the Bell Labs CSP style
Dis source code, archived from the original on 2017-09-21, retrieved 2017-09-20
The design of the Inferno virtual machine, Vita nuova.
"Dis VM design", Inferno (4th ed.), Cat V.
"Dis VM specification", Inferno (4th ed.), Cat V.

[1] "Inferno Application Programming". vitanuova. vitanuova. Retrieved January 26, 2021.

[2] "Dis Virtual Machine Specification". Vita Nuova. 2000. Retrieved 2 February 2015.

[gc-3] Lorenz Huelsbergen and Phil Winterbottomv (1998). "Very Concurrent Mark and Sweep Garbage Collection without Fine-Grain Synchronization" (PDF). 1998 International Symposium on Memory Management.

[1]

[2]

[3]