Preserving version of lowliner's map()

remap.R

remap <- function(.x, .f, ...) {
  .f <- lowliner:::as_function(.f)

  if (inherits(.f, "fseq")) {
    # Handle magrittr's functional sequences
    f_env <- environment(.f)
    f_env$`_function_list` <- map(f_env$`_function_list`, ~ {
      env <- new.env(parent = environment(.))
      environment(.) <- env
      .
    })
    envs <- map(f_env$`_function_list`, environment)
    args <- rep_len(".", length(envs))
  } else {
    env <- new.env(parent = environment(.f))
    environment(.f) <- env
    envs <- list(env)
    args <- names(formals(.f))[1]
  }

  # This active binding ensures that `..` contains the mapped
  # argument. We look it up in the last frame so that we handle
  # functions that evaluate code in special environments like
  # lowliner::when()
  map2(envs, args, function(env, arg) {
    makeActiveBinding("..", function() {
      arg <- get(arg, envir = sys.frame(-1))
      env$`_dotdot`[[1]] <- arg
      env$`_dotdot`
    }, env)
  })

  out <- vector("list", length(.x))
  for (i in seq_along(.x)) {
    each(envs, function(env) {
      env$`_dotdot` <- .x[i]
    })

    res <- .f(.x[[i]], ...)

    stopifnot(is.list(.x) && is.vector(.x))
    out[[i]] <- res
  }

  flatten(out)
}