R: Is a quosure quoting a symbolic, missing or NULL object?

quo-predicates {rlang} | R Documentation

## Is a quosure quoting a symbolic, missing or NULL object?

### Description

These functions examine the expression of a quosure with a predicate.

### Usage

    quo_is_missing(quo)

    quo_is_symbol(quo)

    quo_is_lang(quo)

    quo_is_symbolic(quo)

    quo_is_null(quo)

### Arguments

`quo` | A quosure.

### Empty quosures

When missing arguments are captured as quosures, either through `enquo()` or `quos()`, they are returned as an empty quosure. These quosures contain the missing argument and typically have the empty environment as enclosure.

### Examples

    quo_is_symbol(quo(sym))
    quo_is_symbol(quo(foo(bar)))

    # You can create empty quosures by calling quo() without input:
    quo <- quo()
    quo_is_missing(quo)
    is_missing(f_rhs(quo))

[Package rlang version 0.1.6 Index]