I don't like this sentence. It seems to imply that control structures should only be used inside functions.

Also, there is no reason these couldn't be used in an interactive session. Say I'm making a plot and want to color code my points based on a categorical variable.

```
set.seed(123)
my_dat <- data.frame(x = rnorm(10), y = rnorm(10), z = sample(c("a", "b"), 10, replace = TRUE))
plot(my_dat$x, my_dat$y, col = ifelse(my_dat$z == "a", "blue", "red"))
```