README.md

   1 # frak
   2
   3 frak transforms collections of strings into regular expressions for
   4 matching those strings. The primary goal of this library is to
   5 generate regular expressions from a known set of inputs which avoid
   6 backtracking as much as possible.
   7
   8 ## "Installation"
   9
  10 Add frak as a dependency to your `project.clj` file.
  11
  12 ```clojure
  13 [frak "0.1.1"]
  14 ```
  15
  16 ## Usage
  17
  18 ```clojure
  19 user> (require 'frak)
  20 nil
  21 user> (frak/pattern ["foo" "bar" "baz" "quux"])
  22 #"(?:ba(?:r|z)|foo|quux)"
  23 user> (frak/pattern ["Clojure" "Clojars" "ClojureScript"])
  24 #"Cloj(?:ure(?:Script)?|ars)"
  25 ```
  26
  27 ## How?
  28
  29 A frak pattern is constructed from a trie of characters. As characters
  30 are added to it, meta data is stored in it's branches containing
  31 information such as which branches are terminal and a record of
  32 characters which have "visited" the branch.
  33
  34 During the rendering process frak will prefer branch characters that
  35 have "visited" the most. In the example above, you will notice the
  36 `ba(?:r|z)` branch takes precedence over `foo` even though `"foo"` was
  37 the first to enter the trie. This is because the character `\b` has
  38 frequented the branch more than `\f` and `\q`. The example below
  39 illustrates this behavior on the second character of each input.
  40
  41 ```clojure
  42 user> (frak/pattern ["bit" "bat" "ban" "bot" "bar" "box"])
  43 #"b(?:a(?:t|n|r)|o(?:t|x)|it)"
  44 ```
  45
  46 ## Why?
  47
  48 [Here's](https://github.com/guns/vim-clojure-static/blob/249328ee659190babe2b14cd119f972b21b80538/syntax/clojure.vim#L91-L92)
  49 why. Also because.
  50
  51 ## Next
  52
  53 While the patterns currently generated by frak are correct, there is
  54 potential for improvement; the word trie could be converted to a
  55 directed acyclic word graph (DAWG).
  56
  57 By using a DAWG it might be possible to produce more efficient
  58 patterns which consider common prefixes and suffixes. This could
  59 reduce backtracking and overall pattern size.
  60
  61 ## And now for something completely different
  62
  63 Let's build a regular expression for matching any word in
  64 `/usr/share/dict/words`.
  65
  66 ```clojure
  67 user> (require '[clojure.java.io :as io])
  68 nil
  69 user> (def words
  70            (-> (io/file "/usr/share/dict/words")
  71                io/reader
  72                line-seq))
  73 #'user/words
  74 user> (def word-re (frak/pattern words))
  75 #'user/word-re
  76 user> (every? #(re-matches word-re %) words)
  77 true
  78 ```
  79
  80 You can view the full expression
  81 [here](https://gist.github.com/noprompt/6106573/raw/fcb683834bb2e171618ca91bf0b234014b5b957d/word-re.clj)
  82 (it's approximately `1.5M`!).
  83
  84 ## Benchmarks
  85
  86 ```clojure
  87 (use 'criterium.core)
  88
  89 (def words
  90   (-> (io/file "/usr/share/dict/words")
  91       io/reader
  92       line-seq))
  93
  94 (defn naive-pattern
  95   "Create a naive regular expression pattern for matching every string
  96    in strs."
  97   [strs]
  98   (->> strs
  99        (clojure.string/join "|")
 100        (format "(?:%s)")
 101        re-pattern))
 102
 103 ;; Shuffle 10000 words and build a naive and frak pattern from them.
 104 (def ws (shuffle (take 10000 words)))
 105 (def n-pat (naive-pattern ws))
 106 (def f-pat (frak/pattern ws))
 107
 108 ;; Verify the naive pattern matches everything it was constructed from.
 109 (every? #(re-matches n-pat %) ws)
 110 ;; => true
 111
 112 ;; Shuffle the words again since the naive pattern is built in the
 113 ;; same order as it's inputs.
 114 (def ws' (shuffle ws))
 115
 116 ;;;; Benchmarks
 117
 118 ;; Naive pattern
 119
 120 (bench (doseq [w ws'] (re-matches n-pat w)))
 121 ;;             Execution time mean : 1.499489 sec
 122 ;;    Execution time std-deviation : 181.365166 ms
 123 ;;   Execution time lower quantile : 1.337817 sec ( 2.5%)
 124 ;;   Execution time upper quantile : 1.828733 sec (97.5%)
 125
 126 ;; frak pattern
 127
 128 (bench (doseq [w ws'] (re-matches f-pat w)))
 129 ;;             Execution time mean : 155.515855 ms
 130 ;;    Execution time std-deviation : 5.663346 ms
 131 ;;   Execution time lower quantile : 148.168855 ms ( 2.5%)
 132 ;;   Execution time upper quantile : 164.164294 ms (97.5%)
 133 ```