stringparser: String parser constructor

In parcr: Construct Parsers for Structured Text Files

String parser constructor

Description

Produce a string parser based on stringr::str_match(), to be used with match_s().

Usage

stringparser(match_pattern, reshape = identity, ...)

Arguments

match_pattern	A regular expression that matches the string.
reshape	A function that takes the character vector of captured strings and modifies it to a desired output. By default this is the identity() function.
...	additional parameters passed on to regexec()

Details

This function uses regexec() to produce a string parser. Parsers created with this constructor return the failure signal list() when a string does not match the match_pattern. If the pattern contains captured groups then these groups will be returned as a character vector upon matching. If there is no capture group then the function will return silently upon matching the pattern. You can provide a function to the reshape argument to change the output upon matching.

You always have to wrap the parsers made with this constructor in match_s() to create a parser combinator. I decided not to include this standard pattern in the stringparser constructor itself because it complicates testing of these parsers.

See Also

match_s(), regexec()

Examples

# single capture group
parse_header <- stringparser("^>(\\w+)")
parse_header(">correct_header") # returns "correct_header"
parse_header("> incorrect_header") # returns list()

# multiple capture groups
parse_keyvalue <- stringparser("(\\w+):\\s?(\\w+)")
parse_keyvalue("key1: value1") # returns c("key1", "value1")

# modify output
parse_keyvalue_df <- stringparser(
  "(\\w+):\\s?(\\w+)",
  function(x) data.frame(key = x[1], value = x[2])
)
parse_keyvalue_df("key1: value1") # returns a data frame

parcr documentation built on Feb. 15, 2026, 5:07 p.m.