`as_closure()`

is like `as_function()`

but also wraps primitive
functions inside closures. Some special control flow primitives
like `if`

, `for`

, or `break`

can't be wrapped and will cause an
error.

## Usage

`as_closure(x, env = caller_env())`

## Arguments

- x
A function or formula.

If a

**function**, it is used as is.If a

**formula**, e.g.`~ .x + 2`

, it is converted to a function with up to two arguments:`.x`

(single argument) or`.x`

and`.y`

(two arguments). The`.`

placeholder can be used instead of`.x`

. This allows you to create very compact anonymous functions (lambdas) with up to two inputs. Functions created from formulas have a special class. Use`is_lambda()`

to test for it.If a

**string**, the function is looked up in`env`

. Note that this interface is strictly for user convenience because of the scoping issues involved. Package developers should avoid supplying functions by name and instead supply them by value.- env
Environment in which to fetch the function in case

`x`

is a string.

## Examples

```
# Primitive functions are regularised as closures
as_closure(list)
#> function (...)
#> .Primitive("list")(...)
as_closure("list")
#> function (...)
#> .Primitive("list")(...)
# Operators have `.x` and `.y` as arguments, just like lambda
# functions created with the formula syntax:
as_closure(`+`)
#> function (e1, e2, .x = e1, .y = e2)
#> {
#> if (missing(.x)) {
#> if (missing(e1)) {
#> abort("Must supply `e1` or `.x` to binary operator.")
#> }
#> .x <- e1
#> }
#> else if (!missing(e1)) {
#> abort("Can't supply both `e1` and `.x` to binary operator.")
#> }
#> if (missing(.y) && !missing(e2)) {
#> .y <- e2
#> }
#> else if (!missing(e2)) {
#> abort("Can't supply both `e2` and `.y` to binary operator.")
#> }
#> if (missing(.y))
#> .x
#> else .x + .y
#> }
#> <environment: 0x562ebd2560a8>
as_closure(`~`)
#> function (.x, .y)
#> {
#> if (is_missing(substitute(.y))) {
#> new_formula(NULL, substitute(.x), caller_env())
#> }
#> else {
#> new_formula(substitute(.x), substitute(.y), caller_env())
#> }
#> }
#> <bytecode: 0x562ebcb057d8>
#> <environment: 0x562ebd1a5d68>
```