Convert to function or closure

• as_function() transform objects to functions. It fetches functions by name if supplied a string or transforms formulas to function.

• as_closure() first passes its argument to as_function(). If the result is a primitive function, it regularises it to a proper closure (see is_function() about primitive functions).

as_function(x, env = caller_env())

is_lambda(x)

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 two arguments, .x or . and .y. This allows you to create very compact anonymous functions with up to two inputs. Functions created from formulas have a special class. Use is_lambda() to test for it.
env	Environment in which to fetch the function in case x is a string.

Examples

f <- as_function(~ . + 1)
f(10)
#> [1] 11

# Functions created from a formula have a special class:
is_lambda(f)
#> [1] TRUE
is_lambda(as_function(function() "foo"))
#> [1] FALSE

# Primitive functions are regularised as closures
as_closure(list)
#> function (...) 
#> list(...)
#> <environment: base>
as_closure("list")
#> function (...) 
#> list(...)
#> <environment: base>

# Operators have `.x` and `.y` as arguments, just like lambda
# functions created with the formula syntax:
as_closure(`+`)
#> function(.x, .y) if (missing(.y)) .x else .x + .y
#> <bytecode: 0x7719238>
#> <environment: 0x69f4cc8>
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: 0x45c65a0>
#> <environment: 0x6fd7f78>