Transform to a closure

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: 0x55676066a500>
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: 0x55675e728910>
#> <environment: 0x5567606cc628>