[R] Function in default parameter value closing over variables defined later in the enclosing function

[Ivan Krylov]

Hi!

I needed to generalize a loss function being optimized inside another
function, so I made it a function argument with a default value. It
worked without problems, but later I noticed that the inner function,
despite being defined in the function arguments, somehow closes over a
variable belonging to the outer function, which is defined later.

Example:

outside <- function(inside = function() print(secret)) {
	secret <- 'secret'
	inside()
}
outside()

I'm used to languages that have both lambdas and variable declaration
(like perl5 -Mstrict or C++11), so I was a bit surprised.

Does this work because R looks up the variable by name late enough at
runtime for the `secret` variable to exist in the parent environment of
the `inside` function? Can I rely on it? Is this considered bad style? 
Should I rewrite it (and how)?

-- 
Best regards,
Ivan