在ggplot中使用参数占位符

I am trying to use an argument place holder . within a ggplot(). But it doesn't work for some reason I am not entirely sure of.

What I am doing is this (using the sample data from ggplot2/the tidyverse):

library(tidyverse)
library(magrittr)

corr_eqn <- function(x, y, digits = 2) {
  corr_coef <-
    round(cor(x, y, use = "pairwise.complete.obs"), digits = digits)
  paste("r = ", corr_coef)
}


economics %>%
  filter(date >= "1990-11-01") %>%
  ggplot(aes(pop, unemploy)) +  
  geom_point()+
  annotate(geom = "text", x=-Inf, y=Inf, hjust=0, vjust=1,
           label = economics[economics$date>="1990-11-01",] %$% corr_eqn(pop, unemploy))

However, I want to reduce the command behind label to label = . %$% corr_eqn(pop, unemploy). I.e. I do not want to call economics[economics$date>="1990-11-01",] again as I have already filtered for this:

economics %>%
  filter(date >= "1990-11-01") %>%
  ggplot(aes(pop, unemploy)) +  
  geom_point()+
  annotate(geom = "text", x=-Inf, y=Inf, hjust=0, vjust=1,
           label = . %$% corr_eqn(pop, unemploy))

However, it doesn't work with the argument place holder .. What should I do instead?

Plus, if it would be possible to nat having to list pop and unemploy as seperate arguments in the corr_eqn fn again, this would be also amazing.