This is a maintenance release. The lazyeval package is no longer developed as the tidyverse is switching to tidy evaluation.
Use new registration system.
Switch from SET_NAMED() to
MARK_NOT_MUTABLE() in prevision of an API change in R
core
No longer check the type of the sides of the formula.
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:
f_eval() evaluates a formula in the environment
where it was defined. If supplied, values are first looked for in an
optional data argument. Pronouns .data and
.env can be used to resolve ambiguity in this case. (#43).
Longer forms f_eval_rhs() and f_eval_lhs()
emphasise the side of the formula that you want to evaluate
(#64).
f_interp() provides a full quasiquoting system using
uq() for unquote and uqs() for unquote-splice
(#36).
f_capture() and dots_capture() make it
easy to turn promises and ... into explicit formulas. These
should be used sparingly, as generally lazy-eval is preferred to
non-standard eval.
For functions that work with ...,
f_list() and as_f_list() make it possible to
use the evaluated LHS of a formula to name the elements of a list
(#59).
The core components are accompanied by a number of helper functions:
Identify a formula with is_formula().
Create a formula from a quoted call and an environment with
f_new().
“Unwrap” a formula removing one level from the stack of parent
environments with f_unwrap().
Get or set either side of a formula with f_rhs() or
f_lhs(), and the environment with
f_env().
Convert to text/label with f_text() and
f_label().
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).
lazy_dots() gains .ignore_empty
argument to drop extra arguments (#32).
interp.formula() only accepts single-sided formulas
(#37).
interp() accepts an environment in
.values (#35).
interp.character() always produes a single string,
regardless of input length (#27).
Fixed an infinite loop in
lazy_dots(.follow_symbols = TRUE) (#22, #24)
lazy() now fails with an informative error when it
is applied on an object that has already been evaluated (#23, @lionel-).
lazy() no longer follows the expressions of lazily
loaded objects (#18, @lionel-).
as.lazy_dots() gains a method for NULL, returning a
zero-length list.
auto_names() no longer truncates symbols (#19,
#20)