SmallTalk (60's)

Smalltalk is a computer language designed specifically for a wide range of humans rather than a narrow group of computer specialists. In Smalltalk program flow control structures are simply methods in the class library and most have full source code available for browsing or creating your own variations. As a result of shifting "reserved words" from the language syntax definition into the class library a more flexible and expandable system was realized.

Twenty five years after Smalltalk-80 was released the designers of most other languages (C++, Java, C#, ...) are still not taking advantage of this important dimension of expandability, which means that those other languages lack this important dimension of expandability that Smalltalk not only allows but encourages, extensibility of basic capabilities of the language. The biggest benefit is that it's possible for you to extend the language simply by adding new program flow control structures. At least twenty or so of these extensions have been adopted widely across the various smalltalk versions.