Traditionally, Smalltalk has been described as a pure Object-Oriented programming language, created at Xerox PARC by Alan Kay, Dan Ingalls, Ted Kaehler, and Adele Goldberg. Starting with Smalltalk-71 and ending with the de-facto standard Smalltalk-80. Many other incarnations or versions have been produced since then like Smalltalk/V and Visual Smalltalk (Digitalk), Visual Age (IBM), Dolphin Smalltalk (Object Arts), VisualWorks (Cincom), and Squeak.
Technically, it has been noted that there is no object orientation in Smalltalk since everything is an object (so-called primitive types like integers, booleans, characters, etc. are all instances of a class); nor a language, but rather an environment of living objects.
You can do full Smalltalk development on XO. See the page that explain how to set up the environment. Smalltalk Development on XO
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