snapdragon-lexer    

> Converts a string into an array of tokens, with useful methods for looking ahead and behind, capturing, matching, et cetera.

Please consider following this project's author, Jon Schlinkert, and consider starring the project to show your :heart: and support.

Table of Contents

Install

Install with npm:

``sh
$ npm install --save snapdragon-lexer
`

Breaking changes in v2.0!

Please see the changelog for details!

Usage

`js
const Lexer = require('snapdragon-lexer');
const lexer = new Lexer();

lexer.capture('slash', /^\//);
lexer.capture('text', /^\w+/);
lexer.capture('star', /^\*/);

console.log(lexer.tokenize('foo/*'));
`

API

$3

Create a new Lexer with the given options.

Params

* input {string|Object}: (optional) Input string or options. You can also set input directly on lexer.input after initializing.
* options {object}

Example

`js
const Lexer = require('snapdragon-lexer');
const lexer = new Lexer('foo/bar');
`

$3

Returns true if we are still at the beginning-of-string, and
no part of the string has been consumed.

* returns {boolean}

$3

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

* returns {boolean}

$3

Register a handler function.

Params

* type {string}
* fn {function}: The handler function to register.

Example

`js
lexer.set('star', function() {
// do parser, lexer, or compiler stuff
});
`

$3

Get a registered handler function.

Params

* type {string}
* fn {function}: The handler function to register.

Example

`js
lexer.set('star', function() {
// do lexer stuff
});
const star = lexer.get('star');
`

$3

Returns true if the lexer has a registered handler of the given type.

Params

* {string}: type
* returns {boolean}

Example

`js
lexer.set('star', function() {});
console.log(lexer.has('star')); // true
`

$3

Create a new Token with the given type and value.

Params

* type {string|Object}: (required) The type of token to create
* value {string}: (optional) The captured string
* match {array}: (optional) Match results from String.match() or RegExp.exec()
* returns {Object}: Returns an instance of snapdragon-token

Events

* emits: token

Example

`js
console.log(lexer.token({type: 'star', value: '*'}));
console.log(lexer.token('star', '*'));
console.log(lexer.token('star'));
`

$3

Returns true if the given value is a snapdragon-token instance.

Params

* token {object}
* returns {boolean}

Example

`js
const Token = require('snapdragon-token');
lexer.isToken({}); // false
lexer.isToken(new Token({type: 'star', value: '*'})); // true
`

$3

Consume the given length from lexer.string. The consumed value is used to update lexer.state.consumed, as well as the current position.

Params

* len {number}
* value {string}: Optionally pass the value being consumed.
* returns {String}: Returns the consumed value

Example

`js
lexer.consume(1);
lexer.consume(1, '*');
`

Returns a function for updating a token with lexer
location information.

* returns {function}

$3

Use the given regex to match a substring from lexer.string. 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, which can cause catastrophic backtracking.

Params

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

Example

`js
const lexer = new Lexer('foo/bar');
const match = lexer.match(/^\w+/);
console.log(match);
//=> [ 'foo', index: 0, input: 'foo/bar' ]
`

$3

Scan for a matching substring by calling .match() with the given regex. If a match is found, 1) a token of the specified type is created, 2) match[0] is used as token.value, and 3) the length of match[0] is sliced from lexer.string (by calling .consume()).

Params

* type {string}
* regex {regExp}
* returns {Object}: Returns a token if a match is found, otherwise undefined.

Events

* emits: scan

Example

`js
lexer.string = '/foo/';
console.log(lexer.scan(/^\//, 'slash'));
//=> Token { type: 'slash', value: '/' }
console.log(lexer.scan(/^\w+/, 'text'));
//=> Token { type: 'text', value: 'foo' }
console.log(lexer.scan(/^\//, 'slash'));
//=> Token { type: 'slash', value: '/' }
`

$3

Capture a token of the specified type using the provide regex for scanning and matching substrings. Automatically registers a handler when a function is passed as the last argument.

Params

* type {string}: (required) The type of token being captured.
* regex {regExp}: (required) The regex for matching substrings.
* fn {function}: (optional) If supplied, the function will be called on the token before pushing it onto lexer.tokens.
* returns {Object}

Example

`js
lexer.capture('text', /^\w+/);
lexer.capture('text', /^\w+/, token => {
if (token.value === 'foo') {
// do stuff
}
return token;
});
`

$3

Calls handler type on lexer.string.

Params

* type {string}: The handler type to call on lexer.string
* returns {Object}: Returns a token of the given type or undefined.

Events

* emits: handle

Example

`js
const lexer = new Lexer('/a/b');
lexer.capture('slash', /^\//);
lexer.capture('text', /^\w+/);
console.log(lexer.handle('text'));
//=> undefined
console.log(lexer.handle('slash'));
//=> { type: 'slash', value: '/' }
console.log(lexer.handle('text'));
//=> { type: 'text', value: 'a' }
`

$3

Get the next token by iterating over lexer.handlers and calling each handler on lexer.string until a handler returns a token. If no handlers return a token, an error is thrown with the substring that couldn't be lexed.

* returns {Object}: Returns the first token returned by a handler, or the first character in the remaining string if options.mode is set to character.

Example

`js
const token = lexer.advance();
`

$3

Tokenizes a string and returns an array of tokens.

Params

* input {string}: The string to lex.
* returns {Array}: Returns an array of tokens.

Example

`js
let lexer = new Lexer({ handlers: otherLexer.handlers })
lexer.capture('slash', /^\//);
lexer.capture('text', /^\w+/);
const tokens = lexer.lex('a/b/c');
console.log(tokens);
// Results in:
// [ Token { type: 'text', value: 'a' },
// Token { type: 'slash', value: '/' },
// Token { type: 'text', value: 'b' },
// Token { type: 'slash', value: '/' },
// Token { type: 'text', value: 'c' } ]
`

$3

Push a token onto the lexer.queue array.

Params

* token {object}
* returns {Object}: Returns the given token with updated token.index.

Example

`js
console.log(lexer.queue.length); // 0
lexer.enqueue(new Token('star', '*'));
console.log(lexer.queue.length); // 1
`

$3

Shift a token from lexer.queue.

* returns {Object}: Returns the given token with updated token.index.

Example

`js
console.log(lexer.queue.length); // 1
lexer.dequeue();
console.log(lexer.queue.length); // 0
`

$3

Lookbehind n tokens.

Params

* n {number}
* returns {Object}

Example

`js
const token = lexer.lookbehind(2);
`

$3

Get the previously lexed token.

* returns {Object|undefined}: Returns a token or undefined.

Example

`js
const token = lexer.prev();
`

$3

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

Params

* n {number}
* returns {Object}

Example

`js
const token = lexer.lookahead(2);
`

$3

Lookahead a single token.

* returns {Object}: Returns a token.

Example

`js
const token = lexer.peek();
`

$3

Get the next token, either from the queue or by advancing.

* returns {Object|String}: Returns a token, or (when options.mode is set to character) either gets the next character from lexer.queue, or consumes the next charcter in the string.

Example

`js
const token = lexer.next();
`

$3

Skip n tokens or characters in the string. Skipped values are not enqueued.

Params

* n {number}
* returns {Object}: returns an array of skipped tokens.

Example

`js
const token = lexer.skip(1);
`

$3

Skip tokens while the given fn returns true.

Params

* fn {function}: Return true if a token should be skipped.
* returns {Array}: Returns an array if skipped tokens.

Example

`js
lexer.skipWhile(tok => tok.type !== 'space');
`

$3

Skip the given token types.

Params

* types {string|Array}: One or more token types to skip.
* returns {Array}: Returns an array if skipped tokens.

Example

`js
lexer.skipWhile(tok => tok.type !== 'space');
`

$3

Skip the given token types.

Params

* types {string|Array}: One or more token types to skip.
* returns {Array}: Returns an array if skipped tokens

Example

`js
lexer.skipType('space');
lexer.skipType(['newline', 'space']);
`

$3

Pushes the given token onto lexer.tokens and calls .append() to push token.value onto lexer.stash. Disable pushing onto the stash by setting lexer.options.append or token.append to false.

Params

* token {object|String}
* returns {Object}: Returns the given token.

Events

* emits: push

Example

`js
console.log(lexer.tokens.length); // 0
lexer.push(new Token('star', '*'));
console.log(lexer.tokens.length); // 1
console.log(lexer.stash) // ['*']
`

$3

Append a string to the last element on lexer.stash, or push the string onto the stash if no elements exist.

Params

* value {String}
* returns {String}: Returns the last value in the array.

Example

`js
const stack = new Stack();
stack.push('a');
stack.push('b');
stack.push('c');
stack.append('_foo');
stack.append('_bar');
console.log(stack);
//=> Stack ['a', 'b', 'c_foo_bar']
`

$3

Returns true if a token with the given type is on the stack.

Params

* type {string}: The type to check for.
* returns {boolean}

Example

`js
if (lexer.isInside('bracket') || lexer.isInside('brace')) {
// do stuff
}
`

$3

Throw a formatted error message with details including the cursor position.

Params

* msg {string}: Message to use in the Error.
* node {object}
* returns {undefined}

Example

`js
lexer.set('foo', function(tok) {
if (tok.value !== 'foo') {
throw this.state.error('expected token.value to be "foo"', tok);
}
});
`

$3

Call a plugin function on the lexer instance.

Params

* fn {function}
* returns {object}: Returns the lexer instance.

Example

`js
lexer.use(function(lexer) {
// do stuff to lexer
});
`

$3

Static method that returns true if the given value is an instance of snapdragon-lexer.

Params

* lexer {object}
* returns {Boolean}

Example

`js
const Lexer = require('snapdragon-lexer');
const lexer = new Lexer();
console.log(Lexer.isLexer(lexer)); //=> true
console.log(Lexer.isLexer({})); //=> false
`

$3

Static method that returns true if the given value is an instance of snapdragon-token. This is a proxy to Token#isToken.

Params

* lexer {object}
* returns {Boolean}

Example

`js
const Token = require('snapdragon-token');
const Lexer = require('snapdragon-lexer');
console.log(Lexer.isToken(new Token({type: 'foo'}))); //=> true
console.log(Lexer.isToken({})); //=> false
`

$3

The State class, exposed as a static property.

$3

The Token class, exposed as a static property.

$3

Register a handler function.

Params

* type {String}
* fn {Function}: The handler function to register.

Example

`js
lexer.set('star', function(token) {
// do parser, lexer, or compiler stuff
});
`

As an alternative to .set, the .capture method will automatically register a handler when a function is passed as the last argument.

$3

Get a registered handler function.

Params

* type {String}
* fn {Function}: The handler function to register.

Example

`js
lexer.set('star', function() {
// do parser, lexer, or compiler stuff
});
const star = handlers.get('star');
`

Properties

$3

Type: {boolean}

Default: true (contant)

This property is defined as a convenience, to make it easy for plugins to check for an instance of Lexer.

$3

Type: {string}

Default: ''

The unmodified source string provided by the user.

$3

Type: {string}

Default: ''

The source string minus the part of the string that has already been consumed.

$3

Type: {string}

Default: ''

The part of the source string that has been consumed.

$3

Type: {array}

Default: []

Array of lexed tokens.

$3

Type: {array}

Default: [''] (instance of snapdragon-stack)

Array of captured strings. Similar to the lexer.tokens array, but stores strings instead of token objects.

$3

Type: {array}

Default: []

LIFO (last in, first out) array. A token is pushed onto the stack when an "opening" character or character sequence needs to be tracked. When the (matching) "closing" character or character sequence is encountered, the (opening) token is popped off of the stack.

The stack is not used by any lexer methods, it's reserved for the user. Stacks are necessary for creating Abstract Syntax Trees (ASTs), but if you require this functionality it would be better to use a parser such as [snapdragon-parser][snapdragon-parser], with methods and other conveniences for creating an AST.

$3

Type: {array}

Default: []

FIFO (first in, first out) array, for temporarily storing tokens that are created when .lookahead() is called (or a method that calls .lookhead(), such as .peek()).

Tokens are dequeued when .next() is called.

$3

Type: {Object}

Default: { index: 0, column: 0, line: 1 }

The updated source string location with the following properties.

* index - 0-index
* column - 0-index
* line - 1-index

The following plugins are available for automatically updating tokens with the location:

* snapdragon-location
* snapdragon-position

Options

$3

Type: {string}

Default: undefined

The source of the input string. This is typically a filename or file path, but can also be 'string' if a string or buffer is provided directly.

If lexer.input is undefined, and options.source is a string, the lexer will attempt to set lexer.input by calling fs.readFileSync() on the value provided on options.source.

$3

Type: {string}

Default: undefined

If options.mode is character, instead of calling handlers (which match using regex) the .advance() method will consume and return one character at a time.

$3

Type: {string}

Default: undefined

Specify the token property to use when the .push method pushes a value onto lexer.stash. The logic works something like this:

``js
lexer.append(token[lexer.options.value || 'value']);
`

Tokens

See the snapdragon-token documentation for more details.

Plugins

Plugins are registered with the lexer.use() method and use the following conventions.

$3

Plugins are functions that take an instance of snapdragon-lexer.

However, it's recommended that you always wrap your plugin function in another function that takes an options object. This allow users to pass options when using the plugin. _Even if your plugin doesn't take options, it's a best practice for users to always be able to use the same signature_.

Example

`js
function plugin(options) {
return function(lexer) {
// do stuff
};
}

lexer.use(plugin());
`

About

$3

You might also be interested in these projects:

* snapdragon-scanner: Easily scan a string with an object of regex patterns to produce an array of… more | homepage

$3

Jon Schlinkert

* GitHub Profile
* Twitter Profile
* LinkedIn Profile

$3

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

*

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