Roger Peng provides a lesson on the roots of R and how it got to where it is now:
Chambers was referring to the difficulty in naming and characterizing the S system. Is it a programming language? An environment? A statistical package? Eventually, it seems they settled on “quantitative programming environment”, or in other words, “it’s all the things.” Ironically, for a statistical environment, the first two versions did not contain much in the way of specific statistical capabilities. In addition to a more full-featured statistical modeling system, versions 3 and 4 of the language added the class/methods system for programming (outlined in Chambers’ Programming with Data).
I’m starting feel my age, as some of the “history” feels more like recent experience.
You can also watch Peng’s keynote in the video version.