1# Regular Expression Tokenizer
2
3Tokenizes strings that represent a regular expressions.
4
5[![Build Status](https://secure.travis-ci.org/fent/ret.js.svg)](http://travis-ci.org/fent/ret.js)
6[![Dependency Status](https://david-dm.org/fent/ret.js.svg)](https://david-dm.org/fent/ret.js)
7[![codecov](https://codecov.io/gh/fent/ret.js/branch/master/graph/badge.svg)](https://codecov.io/gh/fent/ret.js)
8
9# Usage
10
11```js
12var ret = require('ret');
13
14var tokens = ret(/foo|bar/.source);
15```
16
17`tokens` will contain the following object
18
19```js
20{
21  "type": ret.types.ROOT
22  "options": [
23    [ { "type": ret.types.CHAR, "value", 102 },
24      { "type": ret.types.CHAR, "value", 111 },
25      { "type": ret.types.CHAR, "value", 111 } ],
26    [ { "type": ret.types.CHAR, "value",  98 },
27      { "type": ret.types.CHAR, "value",  97 },
28      { "type": ret.types.CHAR, "value", 114 } ]
29  ]
30}
31```
32
33# Token Types
34
35`ret.types` is a collection of the various token types exported by ret.
36
37### ROOT
38
39Only used in the root of the regexp. This is needed due to the posibility of the root containing a pipe `|` character. In that case, the token will have an `options` key that will be an array of arrays of tokens. If not, it will contain a `stack` key that is an array of tokens.
40
41```js
42{
43  "type": ret.types.ROOT,
44  "stack": [token1, token2...],
45}
46```
47
48```js
49{
50  "type": ret.types.ROOT,
51  "options" [
52    [token1, token2...],
53    [othertoken1, othertoken2...]
54    ...
55  ],
56}
57```
58
59### GROUP
60
61Groups contain tokens that are inside of a parenthesis. If the group begins with `?` followed by another character, it's a special type of group. A ':' tells the group not to be remembered when `exec` is used. '=' means the previous token matches only if followed by this group, and '!' means the previous token matches only if NOT followed.
62
63Like root, it can contain an `options` key instead of `stack` if there is a pipe.
64
65```js
66{
67  "type": ret.types.GROUP,
68  "remember" true,
69  "followedBy": false,
70  "notFollowedBy": false,
71  "stack": [token1, token2...],
72}
73```
74
75```js
76{
77  "type": ret.types.GROUP,
78  "remember" true,
79  "followedBy": false,
80  "notFollowedBy": false,
81  "options" [
82    [token1, token2...],
83    [othertoken1, othertoken2...]
84    ...
85  ],
86}
87```
88
89### POSITION
90
91`\b`, `\B`, `^`, and `$` specify positions in the regexp.
92
93```js
94{
95  "type": ret.types.POSITION,
96  "value": "^",
97}
98```
99
100### SET
101
102Contains a key `set` specifying what tokens are allowed and a key `not` specifying if the set should be negated. A set can contain other sets, ranges, and characters.
103
104```js
105{
106  "type": ret.types.SET,
107  "set": [token1, token2...],
108  "not": false,
109}
110```
111
112### RANGE
113
114Used in set tokens to specify a character range. `from` and `to` are character codes.
115
116```js
117{
118  "type": ret.types.RANGE,
119  "from": 97,
120  "to": 122,
121}
122```
123
124### REPETITION
125
126```js
127{
128  "type": ret.types.REPETITION,
129  "min": 0,
130  "max": Infinity,
131  "value": token,
132}
133```
134
135### REFERENCE
136
137References a group token. `value` is 1-9.
138
139```js
140{
141  "type": ret.types.REFERENCE,
142  "value": 1,
143}
144```
145
146### CHAR
147
148Represents a single character token. `value` is the character code. This might seem a bit cluttering instead of concatenating characters together. But since repetition tokens only repeat the last token and not the last clause like the pipe, it's simpler to do it this way.
149
150```js
151{
152  "type": ret.types.CHAR,
153  "value": 123,
154}
155```
156
157## Errors
158
159ret.js will throw errors if given a string with an invalid regular expression. All possible errors are
160
161* Invalid group. When a group with an immediate `?` character is followed by an invalid character. It can only be followed by `!`, `=`, or `:`. Example: `/(?_abc)/`
162* Nothing to repeat. Thrown when a repetitional token is used as the first token in the current clause, as in right in the beginning of the regexp or group, or right after a pipe. Example: `/foo|?bar/`, `/{1,3}foo|bar/`, `/foo(+bar)/`
163* Unmatched ). A group was not opened, but was closed. Example: `/hello)2u/`
164* Unterminated group. A group was not closed. Example: `/(1(23)4/`
165* Unterminated character class. A custom character set was not closed. Example: `/[abc/`
166
167
168# Install
169
170    npm install ret
171
172
173# Tests
174
175Tests are written with [vows](http://vowsjs.org/)
176
177```bash
178npm test
179```
180
181# License
182
183MIT
184