How to write compose()

When you use compose(), the functions are passed from right to left — that is to say in the same order as the one you would use in a nested call in base R: the first function to be executed is the function on the right.

In other words, if you are used to the pipe, the order is the opposite one:

# With the pipe
1:28 %>% 
    mean() %>% 
    round()

# In base R
round(mean(1:28))

# With compose
rounded_mean <- compose(round, mean)
rounded_mean(1:28)

So, what's the correct way to write a function that will count the number of NA?