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 very stupid trie of characters.
  30 As characters are added to it, meta data is stored in it's branches.
  31 The meta data contains information such as which branches are terminal
  32 and a record of 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 ## And now for something completely different
  52
  53 Let's build a regular expression for matching any word in
  54 `/usr/share/dict/words`.
  55
  56 ```clojure
  57 user> (require '[clojure.java.io :as io])
  58 nil
  59 user> (def words
  60            (-> (io/file "/usr/share/dict/words")
  61                io/reader
  62                line-seq))
  63 #'user/words
  64 user> (def word-re (frak/pattern words))
  65 #'user/word-re
  66 user> (every? #(re-matches word-re %) words)
  67 true
  68 ```
  69
  70 You can view the full expression
  71 [here](https://gist.github.com/noprompt/6106573/raw/fcb683834bb2e171618ca91bf0b234014b5b957d/word-re.clj)
  72 (it's approximately `1.5M`!).