recursive lag function in tidyverse

gistfile1.txt

library(tidyverse)

# sample data

data <- tibble(
    headcount=c(100,NA,NA)
    ,attrition=rep(.03,3)
    ,hiring=c(10,20,30)
)

# solution
data |> 
    mutate(
        headcount=accumulate2(.x=attrition[-1],.y=hiring[-1],.f=\(prev,.x,.y){  
            out <- prev*(1-.x)+.y
        } 
        ,.init=first(headcount)
        )
    )