. can be regarded as a re-implementation of the . language developed at AT&T by Rick Becker, John Chambers and Allan Wilks. A number of the books and manuals about . bear some relevance to ..
The basic reference is The New . Language: A Programming Environment for Data Analysis and Graphics by Richard A. Becker, John M. Chambers and Allan R. Wilks. The new features of the August 1991 release of . are covered in Statistical Models in . Edited by John M. Chambers and Trevor J. Hastie. In addition, the manuals for ., the commercially supported version of . may be useful.