function_ is a normally-evaluating version of function, which
creates closures. A closure object has three components: the
argument list, the body expression, and the enclosing environment.
arglist() is a helper that produces a named list of
missing_values given a character vector of names.
Usage
function_(args, body, env = arg_env(args, environment()))
arglist(names, fill = missing_value())Arguments
- args
The argument list of the new function. NULL is accepted to make a function with no arguments. Arguments are specified as a named list; the list names become the argument names, and the list values become the default expressions. A value of
missing_value()indicates no default. alist and arglist are useful for making argument lists.- body
An expression for the body of the function.
- env
The enclosing environment of the new function.
- names
A character vector.
- fill
The expression (default missing)
Examples
f1 <- function(x, y = x) { x + y }
f2 <- function_(alist(x = , y = x),
quote( { x + y } ),
environment())
identical(f1, f2) # TRUE
#> [1] TRUE
# `fn` makes a compact way to write functions;
# `fn(x+y)` is equivalent to `function(x, y) x+y`
fn <- function(exp) {
exp_ <- arg(exp)
nn <- arglist(all.names(expr(exp_), functions=FALSE))
function_(nn, expr(exp_), env(exp_))
}
fn(x^2)
#> function (x)
#> x^2
#> <environment: 0x5645f12f1e28>
fn(x+y)
#> function (x, y)
#> x + y
#> <environment: 0x5645f12f1e28>