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Small, prototype-based programming language

Io is a small prototype-based programming language. The ideas in Io are mostly inspired by ANSI Smalltalk (all values are objects) and Act1, Self, and NewtonScript (actors and futures, differential protos, inheritance by delegation).


  • small (~12K lines)
  • pure object language
  • reasonably fast (comparable to Python, Perl, Ruby)
  • differential prototype-based object model
  • untyped
  • incremental garbage collection
  • exceptions
  • ANSI C implementation (except for inline directive)
  • embeddable
  • multi-state (multiple independent VMs can run in the same application)
  • coroutines (light wieght threads)


A beginner's guide is available on Wikibook

"IRC [] " IRC general channel


Download version 2013.12.04 (stable)
released on 4 December 2013

VCS Checkout



LicenseVerified byVerified onNotes
License:BSD 3ClauseJanet Casey6 September 2002

Leaders and contributors

Steve Dekorte Maintainer

Resources and communication

AudienceResource typeURI
Bug Tracking,Developer,Help,
DeveloperVCS Repository Webview
BugsBug Tracking

Software prerequisites

This entry (in part or in whole) was last reviewed on 19 October 2015.


"Bugs" is not in the list (General, Help, Bug Tracking, Support, Developer) of allowed values for the "Resource audience" property.

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