Code highlight themes in knitr: "bipolar"

# function args are keywords c; function names are keywords d
foo = function(arg1 = 100, arg2 = "character string") {
  if (TRUE) {
    x = NULL  # if, function, NULL are keywords a
    for (i in 1:10) x = c(x, mean(3 * rnorm(100) + 1))
  }
}
# <-, = and -> are keywords b
x <- TRUE && FALSE %in% c(T, F)

x = sqrt(-1)  # warning

## Warning: NaNs produced

message("knitr says hello to HTML!")  # message

## knitr says hello to HTML!

1 + "a"  # error

## Error: non-numeric argument to binary operator

Let's ask R what is the value of π? Of course it is 3.1416.