86 lines
3.2 KiB
Markdown
86 lines
3.2 KiB
Markdown
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# lazyeval 0.2.2
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* Fix protection issues from rchk reports.
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# lazyeval 0.2.1
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This is a maintenance release. The lazyeval package is no longer
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developed as the tidyverse is switching to tidy evaluation.
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* Use new registration system.
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* Switch from `SET_NAMED()` to `MARK_NOT_MUTABLE()` in prevision of an
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API change in R core
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* No longer check the type of the sides of the formula.
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# lazyeval 0.2.0
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## Formula-based lazy evaluation
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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.
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There are three key components:
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* `f_eval()` evaluates a formula in the environment where it was defined.
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If supplied, values are first looked for in an optional `data` argument.
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Pronouns `.data` and `.env` can be used to resolve ambiguity in this case.
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(#43). Longer forms `f_eval_rhs()` and `f_eval_lhs()` emphasise the side
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of the formula that you want to evaluate (#64).
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* `f_interp()` provides a full quasiquoting system using `uq()` for unquote
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and `uqs()` for unquote-splice (#36).
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* `f_capture()` and `dots_capture()` make it easy to turn promises
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and `...` into explicit formulas. These should be used sparingly, as
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generally lazy-eval is preferred to non-standard eval.
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* For functions that work with `...`, `f_list()` and `as_f_list()` make it
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possible to use the evaluated LHS of a formula to name the elements of a
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list (#59).
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The core components are accompanied by a number of helper functions:
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* Identify a formula with `is_formula()`.
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* Create a formula from a quoted call and an environment with `f_new()`.
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* "Unwrap" a formula removing one level from the stack of parent environments
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with `f_unwrap()`.
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* Get or set either side of a formula with `f_rhs()` or `f_lhs()`, and
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the environment with `f_env()`.
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* Convert to text/label with `f_text()` and `f_label()`.
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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).
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## Fixes to existing functions
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* `lazy_dots()` gains `.ignore_empty` argument to drop extra arguments (#32).
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* `interp.formula()` only accepts single-sided formulas (#37).
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* `interp()` accepts an environment in `.values` (#35).
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* `interp.character()` always produes a single string, regardless of
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input length (#27).
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* Fixed an infinite loop in `lazy_dots(.follow_symbols = TRUE)` (#22, #24)
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* `lazy()` now fails with an informative error when it is applied on
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an object that has already been evaluated (#23, @lionel-).
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* `lazy()` no longer follows the expressions of lazily loaded objects
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(#18, @lionel-).
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# lazyeval 0.1.10
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* `as.lazy_dots()` gains a method for NULL, returning a zero-length
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list.
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* `auto_names()` no longer truncates symbols (#19, #20)
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