rlang: op-definition – R documentation

Become an expert in R — Interactive courses, Cheat Sheets, certificates and more!

op-definition

Definition operator

Description

The definition operator is typically used in DSL packages like ggvis and data.table. It is also used in the tidyverse as a way of unquoting names (see nse-force).

is_definition() returns TRUE for calls to :=.
is_formulaish() returns TRUE for both formulas and colon-equals operators.

Usage

is_definition(x)

new_definition(lhs, rhs, env = caller_env())

is_formulaish(x, scoped = NULL, lhs = NULL)

Arguments

`x`	An object to test.
`lhs, rhs`	Expressions for the LHS and RHS of the definition.
`env`	The evaluation environment bundled with the definition.

Details

The recommended way to use it is to capture arguments as expressions or quosures. You can then give a special function definition for the := symbol in an overscope. Note that if you capture dots with exprs() or quos(), you need to disable interpretation of := by setting .unquote_names to FALSE.

From rlang and data.table perspectives, this operator is not meant to be evaluated directly at top-level which is why the exported definitions issue an error.

Life cycle

These functions are experimental.

Examples

# A predicate is provided to distinguish formulas from the
# colon-equals operator:
is_definition(quote(a := b))
is_definition(a ~ b)


# is_formulaish() tests for both definitions and formulas:
is_formulaish(a ~ b)
is_formulaish(quote(a := b))

rlang

Functions for Base Types and Core R and 'Tidyverse' Features

v0.4.11

MIT + file LICENSE

Authors

Lionel Henry [aut, cre], Hadley Wickham [aut], mikefc [cph] (Hash implementation based on Mike's xxhashlite), Yann Collet [cph] (Author of the embedded xxHash library), RStudio [cph]

Initial release