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https://github.com/noprompt/frak

Transform collections of strings into regular expressions.
https://github.com/noprompt/frak

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Transform collections of strings into regular expressions.

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# frak



frak transforms collections of strings into regular expressions for

matching those strings. The primary goal of this library is to

generate regular expressions from a known set of inputs which avoid

backtracking as much as possible. It is available as a [command line

utility](#command-line-usage) and for the [browser](#browser-usage)

as a JavaScript library.



## "Installation"



Add frak as a dependency to your `project.clj` file.



[![Clojars Project](https://img.shields.io/clojars/v/frak.svg)](https://clojars.org/frak)



## Clojure(Script) usage



```clojure

user> (require 'frak)

nil

user> (frak/pattern ["foo" "bar" "baz" "quux"])

#"(?:ba[rz]|foo|quux)"

user> (frak/pattern ["Clojure" "Clojars" "ClojureScript"])

#"Cloj(?:ure(?:Script)?|ars)"

user> (frak/pattern ["skill" "skills" "skull" "skulls"])

#"sk(?:[ui]lls?)"

```



## Options

Frak's `pattern` function can accept an options map as its second argument, the available options are:



* `:capture?` - boolean (default false), whether rendered regex should create capture groups for each match

* `:escape-chars` - vector (default see [`frak/metacharacters`](https://github.com/noprompt/frak/blob/3c22d9b33646ca4bc681a5746ac0d11fd06e579b/src/cljx/frak.cljx#L54)), characters to escape when rendering a regular expression.

* `:exact?` - boolean (default false), whether the rendered regex should only produces matches when the entire input string matches.

* `:whole-words?` - boolean (default false), whether the rendered regex should match only whole words (word boundary at both ends of the match) in the input string.



## Command line usage



frak can be used from the command line with either Leiningen or NodeJS.



### With Leiningen



Use the `lein run` command:



```shell

$ lein run -e foo bar baz quux

^(?:ba[rz]|foo|quux)$

```



### With NodeJS



Compile the NodeJS version



```shell

$ lein do cljx once, cljsbuild once node

$ chmod +x bin/frak

$ bin/frak -e foo bar baz quux

^(?:ba[rz]|foo|quux)$

```



## Browser usage



To use frak as a standalone library in the browser with JavaScript

compile the browser version:



```shell

$ lein do cljx once, cljsbuild once browser

$ mv ./target/js/frak.min.js 

```



Try it using this HTML:



```html



  
Input: 


  
Output: 


  

  

  

    var strings = ["foo", "bar", "baz", "quux"];

    // It's a good idea to use the `"exact?"` option.

    var pattern = frak.pattern(strings, {"exact?": true})

    jQuery("#input").text(strings.join(" "));

    jQuery("#output").text(pattern);

  



```



For even more fun try it with [AngularJS](http://angularjs.org/)!



## How?



A frak pattern is constructed from a trie of characters and a

renderer which processes it. As characters are added to the trie, data

such as such as which characters are terminal are stored in it's

branches.



During the rendering process frak analyzes each branch and attempts to

emit the most concise regular expression possible. Additional post

operations are applied after rendering to improve the expression where

possible.



## Why?



[Here's](https://github.com/guns/vim-clojure-static/blob/249328ee659190babe2b14cd119f972b21b80538/syntax/clojure.vim#L91-L92)

why. Also because.



## And now for something completely different



Let's build a regular expression for matching any word in

`/usr/share/dict/words`.



```clojure

user> (require '[clojure.java.io :as io])

nil

user> (def words

           (-> (io/file "/usr/share/dict/words")

               io/reader

               line-seq))

#'user/words

user> (def word-re (frak/pattern words))

#'user/word-re

user> (every? #(re-matches word-re %) words)

true

```



The last two operations will take a moment since there are over

235,000 words to consider.



You can view the full expression

[here](https://gist.github.com/noprompt/6106573/raw/fcb683834bb2e171618ca91bf0b234014b5b957d/word-re.clj)

(it's approximately `1.5M`!).



## Benchmarks



```clojure

(use 'criterium.core)



(def words

  (-> (io/file "/usr/share/dict/words")

      io/reader

      line-seq))



(defn naive-pattern

  "Create a naive regular expression pattern for matching every string

   in strs."

  [strs]

  (->> strs

       (clojure.string/join "|")

       (format "(?:%s)")

       re-pattern))



;; Shuffle 10000 words and build a naive and frak pattern from them.

(def ws (shuffle (take 10000 words)))



(def n-pat (naive-pattern ws))

(def f-pat (frak/pattern ws))



;; Verify the naive pattern matches everything it was constructed from.

(every? #(re-matches n-pat %) ws)

;; => true



;; Shuffle the words again since the naive pattern is built in the

;; same order as it's inputs.

(def ws' (shuffle ws))



;;;; Benchmarks



;; Naive pattern



(bench (doseq [w ws'] (re-matches n-pat w)))

;;             Execution time mean : 1.499489 sec

;;    Execution time std-deviation : 181.365166 ms

;;   Execution time lower quantile : 1.337817 sec ( 2.5%)

;;   Execution time upper quantile : 1.828733 sec (97.5%)



;; frak pattern



(bench (doseq [w ws'] (re-matches f-pat w)))

;;             Execution time mean : 155.515855 ms

;;    Execution time std-deviation : 5.663346 ms

;;   Execution time lower quantile : 148.168855 ms ( 2.5%)

;;   Execution time upper quantile : 164.164294 ms (97.5%)

```