lazyeval

The lazyeval package provides the tools necessary to do non-standard evaluation (NSE) "right" in R. There are three principles:

Instead of using substitute(), use lazyeval::lazy() to capture both the expression and the environment associated with a function argument (aka promise). Or use lazyeval::lazy_dots(...) to capture all the promises in ....
Every function that uses NSE should have a SE partner with a name that ends in _. This function should do all the work. The NSE function should look something like this:
```
# If only y needs NSE
f <- function(x, y) {
  f_(x, lazyeval::lazy(y))
}
```
If needed, make the SE version generic, not the NSE version.
Inside the SE function, use lazyeval::make_call() or lazyeval::lazy_eval() to evalute the expression in the right context.

See the vignette("lazyeval") for more details.

Installation

To install:

devtools::install_github("hadley/lazyeval")