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Limbo is aprogramming language for writing distributed systems and is the language used to writeapplications for theInferno operating system. It was designed atBell Labs bySean Dorward,Phil Winterbottom, andRob Pike.^[1]

The Limbocompiler generatesarchitecture-independentobject code which is then interpreted by theDis 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 byHoare'scommunicating sequential processes (CSP), as implemented and amended in Pike's earlierNewsqueak language and Winterbottom'sAlef.

Limbo supports the following features:

• modular programming
• concurrent programming
• strongtype checking at compile and run-time
• interprocess communication over typedchannels
• automaticgarbage collection
• simpleabstract data types

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 ofreference counting and areal-timegarbage-collector for cyclic data.^[3]

Aspects of the design of Dis were inspired by theAT&T Hobbit microprocessor, as used in the originalBeBox.

Limbo usesAda-style definitions as in:

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

implementCommand;include"sys.m";sys:Sys;include"draw.m";include"sh.m";init(nil:refDraw->Context,nil:listofstring){sys=loadSysSys->PATH;sys->print("Hello World!\n");}

The 3rd edition of the Inferno operating system and Limbo programming language are described in the textbookInferno Programming with LimboISBN 0-470-84352-7 (Chichester: John Wiley & Sons, 2003), byPhillip Stanley-Marbell. Another textbookThe 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.

• TheInferno operating system
• Alef, the predecessor of Limbo
• Plan 9 from Bell Labs, operating system
• Go, similar language from Google
• AT&T Hobbit, a processor architecture which inspired the Dis VM

• Vita Nuova page on Limbo
• A Descent into Limbo byBrian Kernighan
• The Limbo Programming Language byDennis M. Ritchie andAddendum by Vita Nuova.
• Inferno Programming with Limbo byPhillip Stanley-Marbell
• Threaded programming in the Bell Labs CSP style
• Dis source code, archived fromthe original on 2017-09-21, retrieved2017-09-20
• The design of the Inferno virtual machine, Vita nuova, archived from the original on 2025-02-11, retrieved2025-04-28{{citation}}: CS1 maint: bot: original URL status unknown (link).
• "Dis VM design",Inferno (4th ed.), Cat V.
• "Dis VM specification",Inferno (4th ed.), Cat V.

• Concurrent programming languages
• Free and open source compilers
• Inferno (operating system)
• Programming languages created in 1995
• Virtual machines

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