Smalltalk

At Xerox PARC in the early 1970s — the same lab that gave us the GUI, the mouse, and overlapping windows — Alan Kay, with Dan Ingalls and Adele Goldberg, built Smalltalk. Kay’s vision came partly from biology: computing as a mass of small cells that cannot touch each other’s insides and cooperate only by passing messages.

So in Smalltalk everything is an object, and the only thing you ever do is send a message to one. The system is alive and malleable: you inspect and reshape it from inside itself. Crucially, Kay’s definition of object-oriented programming was about messaging and late binding, not the inheritance-heavy thing the term later came to mean. He has said he regrets the word “object” and wishes he had emphasised the messages.

Smalltalk built on Simula 67 (Ole-Johan Dahl and Kristen Nygaard, Oslo, which first brought classes and inheritance to an ALGOL-based language) and radicalised it. Its messaging idea runs straight into The Actor Model and Erlang. (Kay won the Turing Award in 2003.)

Sources

Kay, “The Early History of Smalltalk” (1993) — Kay’s own vivid account of PARC and the idea of messaging.