Python-ish list comprehensions in R [Proof of concept]

list-comprehensions.R

library(purrr)

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Proof-of-concept
# Python style list comprehensions in R
# [ expression for item in list if conditional ]
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
lc <- 'dummy'
class(lc) <- 'listcomprehension'
`[.listcomprehension` <- function(...) {
  ll <- list(...)[-1]
  if (length(ll) == 3L) {
    map_dbl(keep(ll[[2]], ll[[3]]), ll[[1]])
  } else if (length(ll) == 2L) {
    map_dbl(ll[[2]], ll[[1]])
  } else {
    message("Not handled")
    NULL
  }
}



# [x + 1 for x in [1, 2, 3]]
lc[~.x + 1, c(1, 2, 3)]


# [x + 1 for x in [1, 2, 3] if x > 1]
lc[~.x + 1, c(1, 2, 3), ~.x > 1]