Io is a pure object-oriented programming language inspired by Smalltalk, Self, Lisp and NewtonScript. Io has a prototype-based object model similar to the ones in Self and NewtonScript, eliminating the distinction between types and classes. Like Smalltalk, everything is an object and there is dynamic typing. Like Lisp, there are no statements, flow control is achieved using functions, and programs are just data trees. Io uses actors for concurrency, a technique rarely used in modern programming languages. Below are some examples of code in Io:

 //C++ style comments can be used #as can shell-style comments /* and C-style comments */ "Hello world" print //hello world for(i, 1, 10, i print) //prints numbers 1 through 10 x := Object clone //small-talk style object syntax, := used for new slots x = Map clone //when overwriting, = is used. x prettyprint := method( //make a method with no arguments foreach(key, value, write(key, ": ", value, "\n")) //loop through map ) x atPut("hi", 1) //put key-value pair in map x atPut("hello", 2) x prettyprint /* output: hi: 1 hello: 2 */ 

Io was created in 2002 by Steve Dekorte and can be used under a BSD-style licence.

External links

• www.iolanguage.com
• Wikibooks' Io tutorial (http://wikibooks.org/wiki/Programming:Io)