rufoa / named-re

Named capturing group support for clojure regular expressions

named-re

named-re adds support for named capturing groups to regexes in clojure, even when the underlying JRE does not support them directly (e.g. Java 6).

It does this by modifying the clojure.core/re- functions, the clojure.string/replace function, and the #"regex" reader macro.

Installation

named-re is in Clojars. To use it in a Leiningen project, add it to your project.clj dependencies:

[named-re "1.0.0"]

then require named-re.core in your code:

(ns my.example
   (:require named-re.core))

Syntax

named-re uses the same regex syntax as Java 7.

Named groups are denoted by (?<groupname>...). Named backreferences use \k<groupname>. Named groups in replacement strings use ${groupname}.

Usage

named-re augments the normal re- functions in clojure.core.

If a pattern contains any named groups, then the match result will be a map rather than a vector. The keys in the map are the names of the groups. The :0 entry is the entire match (like the 0th item in a match vector).

For example:

(re-find
   #"(?<area>\d{3})-(?<prefix>\d{3})-(?<line>\d{4})"
   "555-123-4567")

gives

{  :0      "555-123-4567",
   :line   "4567",
   :prefix "123",
   :area   "555" } 

Similarly, re-seq will return a list of maps:

(re-seq
   #"(?<title>Mr|Mrs|Miss) (?<forename>\w+) (?<surname>\w+)"
   "Present were Mrs Jane Smith, Mr Joe Bloggs, and Miss Anne Example")

gives

(  {:surname "Smith",   :title "Mrs",  :forename "Jane", :0 "Mrs Jane Smith"}
   {:surname "Bloggs",  :title "Mr",   :forename "Joe",  :0 "Mr Joe Bloggs"}
   {:surname "Example", :title "Miss", :forename "Anne", :0 "Miss Anne Example"} )

Replacements work as expected:

(clojure.string/replace
   "by Alfred V. Aho, Monica S. Lam, Ravi Sethi, and Jeffrey D. Ullman"
   #"(?<first>[A-Z]\w+) (\w\. )*(?<last>[A-Z])\w+"
   "${first} ${last}.")

gives

"by Alfred A., Monica L., Ravi S., and Jeffrey U."

If a pattern does not contain any named groups then these functions behave the normal way.

Caveats

named-re does not use java.util.regex.Pattern and java.util.regex.Matcher objects. This means:

• (instance? java.util.regex.Pattern #"(?<foo>..)") will return false
• (instance? java.util.regex.Matcher (re-matcher #"(?<foo>..)" "abcdef")) will return false
• Java interop cannot be used to invoke methods or access fields directly, e.g. (.reset some-matcher) will throw an exception

License

Copyright © 2013 rufoa

Distributed under the Eclipse Public License, the same as Clojure.