snapdragon-scanner

Easily scan a string with an object of regex patterns to produce an array of tokens. ~100 sloc.

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Install

Install with npm:

$ npm install --save snapdragon-scanner

What is this?

This is a simple Lexical Scanner that takes an object of regex patterns, and uses those patterns to process an input string into an array of tokens.

What is the difference between this and snapdragon-lexer?

snapdragon-lexer uses registered handler functions to capture and handle tokens, snapdragon-scanner simply iterates over an object of regular expression patterns to create tokens. You can think of snapdragon-scanner as the "lite" version of snapdragon-lexer.

Usage

const Scanner = require('snapdragon-scanner');

API

Scanner

Create a new Scanner with the given str and optional rules.

Params

• input {String}: Input string to scan.
• options {Object}: (optional) Pass an object of regex patterns on options.rules, or use .addRules() or .addRule() after instantiating.

Example

const Scanner = require('snapdragon-scanner');
const scanner = new Scanner('var foo = "bar";', {
  rules: {
    space: /^ +/,
    tab: /^\t+/,
    newline: /^\n+/,
    text: /^\w+/,
    equal: /^=/,
    quote: /^["']/,
    semi: /^;/,
    dot: /^\./
  }
});

.addRule

Add a rule to the scanner.

Params

• rule {String}
• match {RegExp}: Match array from RegExp.exec().

Example

console.log(scanner.token('text', ['foo']);
//=> { rule: 'text', value: 'foo', match: [foo] };

.addRule

Add a rule to the scanner.

Params

• rule {String}
• regex {RegExp}: Regular expression to use when scanning.

Example

scanner.addRule(rule, regex);
// example
scanner.addRule('text', /^\w+/);

.addRules

Add an object of rules to the scanner.

Params

• rules {Object}

Example

scanner.addRules({
  text: /^\w+/,
  slash: /^\//,
  dot: /^\./
});

.match

Attempts to match scanner.string with the given regex. Also validates the regex to ensure that it starts with ^ since matching should always be against the beginning of the string, and throws if the regex matches an empty string, to avoid catastrophic backtracking.

Params

• regex {RegExp}: (required)
• returns {Array|null}: Returns the match array or null from RegExp.exec.

Example

const scanner = new Scanner('foo/bar', { text: /^\w+/ });
const match = scanner.match(scanner.rules.get('text'));
console.log(match);
//=> [ 'foo', index: 0, input: 'foo/bar', groups: undefined ]

.consume

Remove the given length of substring from scanner.string.

Params

• len {Number}
• value {String}: Optionally pass the value being consumed for minor performance improvement.
• returns {String}: Returns the consumed value

Example

scanner.consume(1);
scanner.consume(1, '*');

.enqueue

Push a token onto the scanner.queue array.

Params

• token {object}
• returns {Object}: Returns the token.

Example

console.log(scanner.queue.length); // 0
scanner.enqueue({ rule: 'foo' });
console.log(scanner.queue.length); // 1

.dequeue

Shift a token from scanner.queue.

• returns {Object}: Returns the first token in the scanner.queue.

Example

console.log(scanner.queue.length); // 0
scanner.enqueue({ rule: 'foo' });
console.log(scanner.queue.length); // 1
scanner.dequeue();
console.log(scanner.queue.length); // 0

.advance

Iterates over the registered regex patterns until a match is found, then returns a token from the match and regex rule.

• returns {Object}: Returns a token with rule, value and match properties.

Example

const token = scanner.advance();
console.log(token) // { rule: 'text', value: 'foo' }

.lookahead

Lookahead n tokens and return the last token. Pushes any intermediate tokens onto scanner.tokens. To lookahead a single token, use .peek().

Params

• n {number}
• returns {Object}

Example

const token = scanner.lookahead(2);

.peek

Returns a token representing the next match, but without consuming the matched substring (e.g. the cursor position is not advanced).

• returns {Object|undefined}: Returns a token, or undefined if no match was found.

Example

const token = scanner.peek();

.peek

Returns a token representing the next match, but without consuming the matched substring (e.g. the cursor position is not advanced).

• returns {Object|undefined}: Returns a token, or undefined if no match was found.

Example

const token = scanner.peek();

.scan

Returns the next token and advances the cursor position.

• returns {Object|undefined}: Returns a token, or undefined if no match was found.

Example

const token = scanner.scan();

.scanWhile

Scan until the given fn does not return true.

Params

• fn {Function}: Must return true to continue scanning.
• returns {Array}: Returns an array if scanned tokens.

Example

scanner.scanWhile(tok => tok.rule !== 'space');

.bos

Returns true if the scanner has not consumed any of the input string.

• returns {Boolean}

.eos

Returns true if scanner.string and scanner.queue are empty.

• returns {Boolean}

Token objects

Scanner tokens are plain JavaScript objects with the following properties:

{
  type: String;
  value: String
  match: Array
}

Token properties

• type {String} - The name of the regex that matched the substring.
• value {String} - The substring that was captured by the regex.
• match {Array} - The match array from RegExp.exec()

Release history

See the changelog.

About

Pull requests and stars are always welcome. For bugs and feature requests, please create an issue.

Running and reviewing unit tests is a great way to get familiarized with a library and its API. You can install dependencies and run tests with the following command:

$ npm install && npm test

(This project's readme.md is generated by verb, please don't edit the readme directly. Any changes to the readme must be made in the .verb.md readme template.)

To generate the readme, run the following command:

$ npm install -g verbose/verb#dev verb-generate-readme && verb

Related projects

You might also be interested in these projects:

• snapdragon-lexer: Converts a string into an array of tokens, with useful methods for looking ahead and… more | homepage
• snapdragon-node: Snapdragon utility for creating a new AST node in custom code, such as plugins. | homepage
• snapdragon-token: Create a snapdragon token. Used by the snapdragon lexer, but can also be used by… more | homepage

Author

Jon Schlinkert

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License

Copyright © 2018, Jon Schlinkert. Released under the MIT License.

This file was generated by verb-generate-readme, v0.8.0, on November 19, 2018.