as_function
Convert to function or closure
Description
-
as_function()transforms a one-sided formula into a function. This powers the lambda syntax in packages like purrr. -
as_closure()first passes its argument toas_function(). If the result is a primitive function, it regularises it to a proper closure (seeis_function()about primitive functions). Some special control flow primitives likeif,for, orbreakcan't be coerced to a closure.
Usage
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. Lambdas currently do not support nse-force, due to the way the arguments are handled internally. |
env |
Environment in which to fetch the function in case |
Examples
f <- as_function(~ .x + 1)
f(10)
g <- as_function(~ -1 * .)
g(4)
h <- as_function(~ .x - .y)
h(6, 3)
# Functions created from a formula have a special class:
is_lambda(f)
is_lambda(as_function(function() "foo"))
# Primitive functions are regularised as closures
as_closure(list)
as_closure("list")
# Operators have `.x` and `.y` as arguments, just like lambda
# functions created with the formula syntax:
as_closure(`+`)
as_closure(`~`)
# Use a regular function for tidy evaluation, also when calling functions
# that use tidy evaluation:
## Bad:
e <- as_function(~ as_label(ensym(.x)))
## Good:
e <- as_function(function(x) as_label(ensym(x)))
e(y)