Every expression in R can be rewritten as a function call. However, R has some special syntax to write common operations like assignments, lookups, and numerical expressions more naturally. This chapter gives an overview of how to write valid R expressions. It’s not intended to be a formal or complete description of all valid syntax in R, but just a readable description of how to write valid R expressions.[18]
[18] You could write R code as a series of function calls with lots of function calls. This would look a lot like LISP code, with all the parentheses. Incidentally, the S language was inspired by LISP and uses many of the same data structures and evaluation techniques that are used by LISP interpreters.