ternary op in R

ternary.R

lobstr::ast(T ? F : 1)

`%?%` <- function(e1, e2) {
  e2_expr <- substitute(e2)
  if (e1) {
    return(eval.parent(e2_expr[[2]]))
  } else {
    return(eval.parent(e2_expr[[3]]))
  }
}

`?` <- function(e1, e2) {
  e1_expr <- substitute(e1)
  if (missing(e2)) {
    return(do.call(utils::`?`, list(e1_expr)))
  }
  e2_expr <- substitute(e2)
  e1_is_sym <- is.symbol(e1_expr)
  e2_is_colon_call <- is.call(e2_expr) && identical(e2_expr[[1]], quote(`:`))
  if (!e1_is_sym) {
    return(eval.parent(substitute(`%?%`(e1_expr, e2_expr))))
  }
  if (!e2_is_colon_call) {
    return(do.call(utils::`?`, list(e1_expr, e2_expr)))
  }
  e1_is_help <- !exists(e1_expr, parent.frame())
  if (e1_is_help) {
    return(do.call(utils::`?`, list(e1_expr, e2_expr)))
  }
  e1_val <- eval.parent(e1_expr)
  e1_is_cond <- isTRUE(e1_val) || isFALSE(e1_val)
  if (e1_is_cond) {
    warning("`", deparse(e1_expr), "` is ambiguous!", call. = FALSE)
    return(eval.parent(substitute(`%?%`(e1_expr, e2_expr))))
  } else {
    return(do.call(utils::`?`, list(e1_expr, e2_expr)))
  }
}

1 == 1 ? "y" : "n"
#> [1] "y"
1 == 2 ? "y" : "n"
#> [1] "n"