exec {rlang}

Execute a function

Description

This function constructs and evaluates a call to .fn. It has two primary uses:

• To call a function with arguments stored in a list (if the function doesn't support dynamic dots). Splice the list of arguments with ⁠!!!⁠.

• To call every function stored in a list (in conjunction with map()/ lapply())

Usage

exec(.fn, ..., .env = caller_env())

Arguments

.fn

A function, or function name as a string.

...

<dynamic> Arguments for .fn.

.env

Environment in which to evaluate the call. This will be most useful if .fn is a string, or the function has side-effects.

Examples

args <- list(x = c(1:10, 100, NA), na.rm = TRUE)
exec("mean", !!!args)
exec("mean", !!!args, trim = 0.2)

fs <- list(a = function() "a", b = function() "b")
lapply(fs, exec)

# Compare to do.call it will not automatically inline expressions
# into the evaluated call.
x <- 10
args <- exprs(x1 = x + 1, x2 = x * 2)
exec(list, !!!args)
do.call(list, args)

# exec() is not designed to generate pretty function calls. This is
# most easily seen if you call a function that captures the call:
f <- disp ~ cyl
exec("lm", f, data = mtcars)

# If you need finer control over the generated call, you'll need to
# construct it yourself. This may require creating a new environment
# with carefully constructed bindings
data_env <- env(data = mtcars)
eval(expr(lm(!!f, data)), data_env)