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#' Partially evaluate an expression.
#'
#' This function partially evaluates an expression, using information from
#' the tbl to determine whether names refer to local expressions
#' or remote variables. This simplifies SQL translation because expressions
#' don't need to carry around their environment - all relevant information
#' is incorporated into the expression.
#'
#' @section Symbol substitution:
#'
#' `partial_eval()` needs to guess if you're referring to a variable on the
#' server (remote), or in the current environment (local). It's not possible to
#' do this 100% perfectly. `partial_eval()` uses the following heuristic:
#'
#' \itemize{
#' \item If the tbl variables are known, and the symbol matches a tbl
#' variable, then remote.
#' \item If the symbol is defined locally, local.
#' \item Otherwise, remote.
#' }
#'
#' You can override the guesses using `local()` and `remote()` to force
#' computation, or by using the `.data` and `.env` pronouns of tidy evaluation.
#'
#' @param call an unevaluated expression, as produced by [quote()]
#' @param data A lazy data frame backed by a database query.
#' @param env environment in which to search for local values
#' @param vars `r lifecycle::badge("deprecated")`: Pass a lazy frame to `data`
#' instead.
#' @export
#' @keywords internal
#' @examples
#' lf <- lazy_frame(year = 1980, id = 1)
#' partial_eval(quote(year > 1980), data = lf)
#'
#' ids <- c("ansonca01", "forceda01", "mathebo01")
#' partial_eval(quote(id %in% ids), lf)
#'
#' # cf.
#' partial_eval(quote(id == .data$id), lf)
#'
#' # You can use local() or .env to disambiguate between local and remote
#' # variables: otherwise remote is always preferred
#' year <- 1980
#' partial_eval(quote(year > year), lf)
#' partial_eval(quote(year > local(year)), lf)
#' partial_eval(quote(year > .env$year), lf)
#'
#' # Functions are always assumed to be remote. Use local to force evaluation
#' # in R.
#' f <- function(x) x + 1
#' partial_eval(quote(year > f(1980)), lf)
#' partial_eval(quote(year > local(f(1980))), lf)
partial_eval <- function(call,
data,
env = caller_env(),
vars = deprecated(),
error_call) {
if (lifecycle::is_present(vars)) {
lifecycle::deprecate_stop("2.1.2", "partial_eval(vars)")
}
if (is.character(data)) {
lifecycle::deprecate_stop("2.1.2", "partial_eval(data = 'must be a lazy frame')", )
}
if (is_sql_literal(call)) {
call
} else if (is_symbol(call)) {
partial_eval_sym(call, data, env)
} else if (is_quosure(call)) {
partial_eval(get_expr(call), data, get_env(call), error_call = error_call)
} else if (is_call(call, "if_any")) {
out <- partial_eval_if(call, data, env, reduce = "|", error_call = error_call)
expr(((!!out)))
} else if (is_call(call, "if_all")) {
out <- partial_eval_if(call, data, env, reduce = "&", error_call = error_call)
expr(((!!out)))
} else if (is_call(call, "across")) {
partial_eval_across(call, data, env, error_call)
} else if (is_call(call, "pick")) {
partial_eval_pick(call, data, env, error_call)
} else if (is_call(call)) {
partial_eval_call(call, data, env)
} else {
cli_abort("Unknown input type: {typeof(call)}")
}
}
is_sql_literal <- function(x) {
is_atomic(x) || is_null(x) || blob::is_blob(x)
}
capture_dot <- function(.data, x) {
partial_eval(enquo(x), data = .data)
}
partial_eval_dots <- function(.data,
...,
# .env = NULL,
.named = TRUE,
error_call = caller_env()) {
# corresponds to `capture_dots()`
# browser()
dots <- as.list(enquos(..., .named = .named))
dot_names <- names2(exprs(...))
was_named <- have_name(exprs(...))
for (i in seq_along(dots)) {
dot <- dots[[i]]
# if (!is_null(.env)) {
# dot <- quo_set_env(dot, .env)
# }
dot_name <- dot_names[[i]]
dots[[i]] <- partial_eval_quo(dot, .data, error_call, dot_name, was_named[[i]])
}
# Remove names from any list elements
is_list <- purrr::map_lgl(dots, is.list)
names2(dots)[is_list] <- ""
# Auto-splice list results from partial_eval_quo()
dots[!is_list] <- lapply(dots[!is_list], list)
unlist(dots, recursive = FALSE)
}
partial_eval_quo <- function(x, data, error_call, dot_name, was_named) {
# no direct equivalent in `dtplyr`, mostly handled in `dt_squash()`
withCallingHandlers(
expr <- partial_eval(get_expr(x), data, get_env(x), error_call = error_call),
error = function(cnd) {
label <- expr_as_label(x, dot_name)
msg <- c(i = "In argument: {.code {label}}")
cli_abort(msg, call = error_call, parent = cnd)
}
)
if (is.list(expr)) {
if (was_named) {
msg <- c(
"In dbplyr, the result of `across()` must be unnamed.",
i = "`{dot_name} = {as_label(x)}` is named."
)
cli_abort(msg, call = error_call)
}
lapply(expr, new_quosure, env = get_env(x))
} else {
new_quosure(expr, get_env(x))
}
}
partial_eval_sym <- function(sym, data, env) {
vars <- op_vars(data)
name <- as_string(sym)
if (name %in% vars) {
sym
} else if (env_has(env, name, inherit = TRUE)) {
# Inline the value so that the translation function can choose what to do
val <- eval_bare(sym, env)
if (is_atomic(val)) {
val <- unname(val)
}
val
} else {
cli::cli_abort(
"Object {.var {name}} not found.",
call = NULL
)
}
}
is_mask_pronoun <- function(call) {
is_call(call, c("$", "[["), n = 2) && is_symbol(call[[2]], c(".data", ".env"))
}
partial_eval_call <- function(call, data, env) {
fun <- call[[1]]
# Try to find the name of inlined functions
if (inherits(fun, "inline_colwise_function")) {
vars <- colnames(tidyselect_data_proxy(data))
dot_var <- vars[[attr(call, "position")]]
call <- replace_sym(attr(fun, "formula")[[2]], c(".", ".x"), sym(dot_var))
env <- get_env(attr(fun, "formula"))
} else if (is.function(fun)) {
fun_name <- find_fun(fun)
if (is.null(fun_name)) {
# This probably won't work, but it seems like it's worth a shot.
return(eval_bare(call, env))
}
call[[1]] <- fun <- sym(fun_name)
}
# Compound calls, apart from `::` aren't translatable
if (is_call(fun) && !is_call(fun, "::")) {
if (is_mask_pronoun(fun)) {
stop("Use local() or remote() to force evaluation of functions", call. = FALSE)
} else {
return(eval_bare(call, env))
}
}
# .data$, .data[[]], .env$, .env[[]] need special handling
if (is_mask_pronoun(call)) {
var <- call[[3]]
if (is_call(call, "[[")) {
var <- sym(eval(var, env))
}
if (is_symbol(call[[2]], ".data")) {
var
} else {
eval_bare(var, env)
}
} else {
# Process call arguments recursively, unless user has manually called
# remote/local
if (is_call(call, "local")) {
eval_bare(call[[2]], env)
} else if (is_call(call, "remote")) {
call[[2]]
} else if (is_call(call, "$")) {
# Only the 1st argument is evaluated
call[[2]] <- partial_eval(call[[2]], data = data, env = env)
call
} else {
call[-1] <- lapply(call[-1], partial_eval, data = data, env = env)
call
}
}
}
find_fun <- function(fun) {
if (is_lambda(fun)) {
body <- body(fun)
if (!is_call(body)) {
return(NULL)
}
fun_name <- body[[1]]
if (!is_symbol(fun_name)) {
return(NULL)
}
as.character(fun_name)
} else if (is.function(fun)) {
fun_name(fun)
}
}
fun_name <- function(fun) {
# `dtplyr` uses the same idea but needs different environments
pkg_env <- env_parent(global_env())
known <- c(ls(base_agg), ls(base_scalar))
for (x in known) {
if (!env_has(pkg_env, x, inherit = TRUE))
next
fun_x <- env_get(pkg_env, x, inherit = TRUE)
if (identical(fun, fun_x))
return(sym(x))
}
NULL
}
replace_sym <- function(call, sym, replace) {
if (is_symbol(call, sym)) {
if (is_list(replace)) {
replace[[match(as_string(call), sym)]]
} else {
replace
}
} else if (is_call(call)) {
call[] <- lapply(call, replace_sym, sym = sym, replace = replace)
call
} else {
call
}
}
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