Code manipulation tools

[hadley]

If you think of code as a tree, what functions do you need to manipulate it? What parallels exist between lazyeval and xml2 + purrr?

[hadley]

Would be useful to have have something like:

is_call <- function(x, call, n_params) {
}

And ability to match deeper AST trees - but need to be parameterised/templatised somehow.