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A general description is here.
New print() (S3) method for class "function", also used for auto-printing. Further, .Primitive functions now print and auto-print identically. The new method is based on code suggestions by Romain Franççois.
contr.sum() etc gain an argument 'sparse' which allows sparse matrices to be returned.
contrasts() also gains a 'sparse' argument which it passes to the actual contrast function if that has a formal argument 'sparse'.
'contrasts(f, .) <- val' now also works when 'val' is a sparse Matrix. It is planned that model.matrix() will work with such factors 'f' in the future.
gregexpr() no longer segfaults when "" is given as the search pattern. Thanks to Hervéé Pagèès for the bug report.
CHAR() now returns (const char *) since CHARSXPs should no longer be modified in place. This change allows compilers to warn or error about improper modification. Thanks to Hervéé Pagèès for the suggestion.