lazyeval 0.2.0

Formula-based lazy evaluation

Lazyeval has a new system for lazy-eval based on formulas, described in depth in the new lazyeval vignette. This system is still a little experimental - it hasn't seen much use outside of the vignette, so it certainly may change a little in the future. However, long-term goal is to use these tools across all of my packages (ggplot2, tidyr, dplyr, etc), and I am fairly confident that this is a robust system that won't need major changes.

There are three key components:

The core components are accompanied by a number of helper functions:

I've also added expr_find(), expr_text() and expr_label() explicitly to find the expression associated with a function argument, and label it for output (#58). This is one of the primary uses cases for NSE. expr_env() is a similar helper that returns the environment associated with a promise (#67).

Fixes to existing functions

lazyeval 0.1.10