recursive: Make the regular expression recursive.

In rebus.base: Core Functionality for the 'rebus' Package

Description

Makes the regular expression (or part of it) recursive.

Usage

recursive(x)

Arguments

x	A character vector.

Value

A character vector representing part or all of a regular expression.

Note

Recursion is not supported by R's internal PRCE engine or stringi's ICU engine.

References

http://www.regular-expressions.info/recurse.html and http://www.rexegg.com/regex-recursion.html

Examples

recursive("a")

# Recursion isn't supported by R's PRCE engine or
# stringi/stringr's ICU engine
x <- c("ab222z", "ababz", "ab", "abab")
rx <- "ab(?R)?z"
grepl(rx, x, perl = TRUE)
try(grepl(rx, x))
try(stringi::stri_detect_regex(x, rx))

Example output

<regex> a(?R)
[1] FALSE  TRUE FALSE FALSE
Error in grepl(rx, x) : 
  invalid regular expression 'ab(?R)?z', reason 'Invalid regexp'
Error in stringi::stri_detect_regex(x, rx) : 
  Syntax error in regexp pattern. (U_REGEX_RULE_SYNTAX)

rebus.base documentation built on May 2, 2019, 5:14 a.m.