Evaluate a function while injecting some locals.

Instead of modifying a closure's parent environment directly, sometimes it may be desirable to do a one-time injection that overrides what would normally be accessible through the closure. call_with allows this by extending the usual do.call to a third argument that is a list or environment temporarily injected during the course of the call.

call_with(fn, args, with)

Arguments

fn	function.
args	list. The arguments to call the fn with.
with	list or environment. Additional locals to make available during the call.

Value

The result of calling fn with the injection provided by the with parameter.

Examples

not_run({
  fn <- local({ x <- 1; function(y) { x + y } })
  stopifnot(fn(1) == 2)
  stopifnot(call_with(fn, list(1), list(x = 2)) == 3)
})