store: Store and retrieve objects

In parcr: Construct Parsers for Structured Text Files

Store and retrieve objects

Description

Sometimes you want to use a parsed object to modify a later parser operation, as in the example below. The store() and retrieve() functions provide the tools to create such a parser.

Usage

store(name, value)

retrieve(name)

Arguments

name	a string used as the name of the stored object.
value	object to be stored.

Value

Nothing for store() and the stored object for retrieve().

Examples

parse_nr <- function(line) {
  m <- stringr::str_extract(line, "number=(\\d+)", group=1)
  if (is.na(m)) list()
  else store("nr", as.numeric(m))
}

p <- function() {
  match_s(parse_nr) %then%
    exactly(retrieve("nr"), literal("A"))
}

p()(c("number=3", "A", "A", "A")) # success
p()(c("number=2", "A", "A", "A")) # failure

parcr documentation built on Aug. 8, 2025, 6:20 p.m.