Lionel Henry lionel-

Summary of meeting between Tidyverse members and Luke Tierney at useR! 2024.

Frame/Environment inspection

Frontends and low level tools need to know what kind of bindings they are dealing with. Objectives include:

Avoiding side effects such as triggering a promise or causing a missing argument error. Low level tools often can't afford to protect against those for every variable lookup. Figuring out what happened by inspecting errors is also ambiguous, and sometimes impossible (promises may cause longjumps in a variety of ways).
Transparency in debugging/development settings. Providing context to the user about what's going to happen if they attempt to retrieve the value of a binding (i.e. an active binding invokation, a promise forcing leading to the evaluation of such and such expression, etc).

	# Prototype of `source()` as currently implemented
	source2 <- function(file, env = parent.frame()) {
	exprs <- parse(file)
	for (expr in exprs) {
	eval(expr, env)
	}
	}

	# Prototype of `source()` using an evaluation strategy where the
	# unwinding scope is the whole file rather than each line

	makeDelayedBinding <- function(sym,
	expr,
	eval.env = parent.frame(1),
	assign.env = parent.frame(1)) {
	expr <- substitute(expr)

	value <- NULL
	forced <- FALSE

	forceDelayed <- function() {

	# The general idea is to supply a recoding specification through a
	# data frame of keys and values. They keys are a generalisation of
	# names, they can be any type.


	keys <- function(key, value) {
	tibble::tibble(.key = key, .value = value)
	}
	dribbleys <- function(...) {
	tibble::tribble(~ .key, ~ .value, ...)

	# Simple DT wrapper
	summarise <- function(data, j, by) {
	data <- data.table::as.data.table(data)
	data[
	i = ,
	j = eval(substitute(j)),
	by = eval(substitute(by))
	]
	}



	truncate_len <- function(x, n) {
	if (length(x) < n) {
	stop("Can't truncate vector to the given length because it is already shorter")
	}
	x[seq_len(n)]
	}
	truncate_along <- function(x, y) {
	truncate_len(x, length(y))

	Homebrew build logs for [email protected] on macOS 13
	Build date: 2023-04-02 14:50:46

	# Actually does not work because quosured magrittr pronouns are not
	# evaluated in the right environment


	library("magrittr")
	library("rlang")

	# Anticipate renaming of `quo_is_lang()` in rlang
	quo_is_call <- quo_is_lang


	depend <- function(..., character.only = FALSE) {
	# Mimic library()'s UI
	if (character.only) {
	packages <- c(...)
	} else {
	packages <- substitute(c(...))[-1]
	if (!all(vapply(packages, is.symbol, logical(1)))) {
	stop("Can't supply expressions if `character.only` is FALSE")
	}