snapdragon    

> Easy-to-use plugin system for creating powerful, fast and versatile parsers and compilers, with built-in source-map support.

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
`

Created by jonschlinkert and doowb.

Features

* Bootstrap your own parser, get sourcemap support for free
* All parsing and compiling is handled by simple, reusable middleware functions
* Inspired by the parsers in pug and css.

Quickstart example

All of the examples in this document assume the following two lines of setup code exist first:

`js
var Snapdragon = require('snapdragon');
var snapdragon = new Snapdragon();
`

Parse a string

`js
var ast = snapdragon.parser
// parser handlers (essentially middleware)
// used for parsing substrings to create tokens
.set('foo', function () {})
.set('bar', function () {})
.parse('some string', options);
`

Compile an AST returned from .parse()

`js
var result = snapdragon.compiler
// compiler handlers (essentially middleware),
// called on a node when the node.type matches
// the name of the handler
.set('foo', function () {})
.set('bar', function () {})
// pass the ast from the parse method
.compile(ast)

// the compiled string
console.log(result.output);
`

See the examples.

Parsing

Parser handlers

Parser handlers are middleware functions responsible for matching substrings to create tokens:

Example handler

`js
var ast = snapdragon.parser
.set('dot', function() {
var pos = this.position();
var m = this.match(/^\./);
if (!m) return;
return pos({
// the "type" will be used by the compiler later on,
// we'll go over this in the compiler docs
type: 'dot',
// "val" is the string captured by ".match",
// in this case that would be '.'
val: m[0]
});
})
.parse('.'[, options])
`

_As a side node, it's not scrictly required to set the type on the token, since the parser will add it to the token if it's undefined, based on the name of the handler. But it's good practice since tokens aren't always returned._

Example token

And the resulting tokens look something like this:

`js
{
type: 'dot',
val: '.'
}
`

Position

Next, pos() is called on the token as it's returned, which patches the token with the position of the string that was captured:

`js
{ type: 'dot',
val: '.',
position:
{ start: { lineno: 1, column: 1 },
end: { lineno: 1, column: 2 } }}
`

Life as an AST node

When the token is returned, the parser pushes it onto the nodes array of the "previous" node (since we're in a tree, the "previous" node might be literally the last node that was created, or it might be the "parent" node inside a nested context, like when parsing brackets or something with an open or close), at which point the token begins its life as an AST node.

Wrapping up

In the parser calls all handlers and cannot find a match for a substring, an error is thrown.

Assuming the parser finished parsing the entire string, an AST is returned.

Compiling

The compiler's job is to take the AST created by the parser and convert it to a new string. It does this by iterating over each node on the AST and calling a function on the node based on its type.

This function is called a "handler".

Compiler handlers

Handlers are _named_ middleware functions that are called on a node when node.type matches the name of a registered handler.

`js
var result = snapdragon.compiler
.set('dot', function (node) {
console.log(node.val)
//=> '.'
return this.emit(node.val);
})
`

If node.type does not match a registered handler, an error is thrown.

Source maps

If you want source map support, make sure to emit the entire node as the second argument as well (this allows the compiler to get the node.position).

`js
var res = snapdragon.compiler
.set('dot', function (node) {
return this.emit(node.val, node);
})
`

All together

This is a very basic example, but it shows how to parse a dot, then compile it as an escaped dot.

`js
var Snapdragon = require('..');
var snapdragon = new Snapdragon();

var ast = snapdragon.parser
.set('dot', function () {
var pos = this.position();
var m = this.match(/^\./);
if (!m) return;
return pos({
type: 'dot',
val: m[0]
})
})
.parse('.')

var result = snapdragon.compiler
.set('dot', function (node) {
return this.emit('\\' + node.val);
})
.compile(ast)

console.log(result.output);
//=> '\.'
`

API

$3

Create a new Parser with the given input and options.

Params

* input {String}
* options {Object}

Example

`js
var Snapdragon = require('snapdragon');
var Parser = Snapdragon.Parser;
var parser = new Parser();
`

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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
parser.set('foo', function(node) {
if (node.val !== 'foo') {
throw this.error('expected node.val to be "foo"', node);
}
});
`

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Define a non-enumberable property on the Parser instance. This is useful in plugins, for exposing methods inside handlers.

Params

* key {String}: propery name
* val {any}: property value
* returns {Object}: Returns the Parser instance for chaining.

Example

`js
parser.define('foo', 'bar');
`

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Create a new Node with the given val and type.

Params

* val {Object}
* type {String}
* returns {Object}: returns the Node instance.

Example

`js
parser.node('/', 'slash');
`

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Mark position and patch node.position.

* returns {Function}: Returns a function that takes a node

Example

`js
parser.set('foo', function(node) {
var pos = this.position();
var match = this.match(/foo/);
if (match) {
// call pos with the node
return pos(this.node(match[0]));
}
});
`

$3

Add parser type with the given visitor fn.

Params

* type {String}
* fn {Function}

Example

`js
parser.set('all', function() {
var match = this.match(/^./);
if (match) {
return this.node(match[0]);
}
});
`

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Get parser type.

Params

* type {String}

Example

`js
var fn = parser.get('slash');
`

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Push a node onto the stack for the given type.

Params

* type {String}
* returns {Object} token

Example

`js
parser.set('all', function() {
var match = this.match(/^./);
if (match) {
var node = this.node(match[0]);
this.push(node);
return node;
}
});
`

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Pop a token off of the stack of the given type.

Params

* type {String}
* returns {Object}: Returns a token

Example

`js
parser.set('close', function() {
var match = this.match(/^\}/);
if (match) {
var node = this.node({
type: 'close',
val: match[0]
});

this.pop(node.type);
return node;
}
});
`

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Return true if inside a "set" of the given type. Sets are created manually by adding a type to parser.sets. A node is "inside" a set when an .open node for the given type was previously pushed onto the set. The type is removed from the set by popping it off when the .close node for the given type is reached.

Params

* type {String}
* returns {Boolean}

Example

`js
parser.set('close', function() {
var pos = this.position();
var m = this.match(/^\}/);
if (!m) return;
if (!this.isInside('bracket')) {
throw new Error('missing opening bracket');
}
});
`

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Return true if node is the given type.

Params

* node {Object}
* type {String}
* returns {Boolean}

Example

`js
parser.isType(node, 'brace');
`

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Get the previous AST node from the parser.stack (when inside a nested context) or parser.nodes.

* returns {Object}

Example

`js
var prev = this.prev();
`

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Match regex, return captures, and update the cursor position by match[0] length.

Params

* regex {RegExp}
* returns {Object}

Example

`js
// make sure to use the starting regex boundary: "^"
var match = this.match(/^\./);
`

Params

* input {String}
* returns {Object}: Returns an AST with ast.nodes

Example

`js
var ast = parser.parse('foo/bar');
`

$3

Create a new Compiler with the given options.

Params

* options {Object}
* state {Object}: Optionally pass a "state" object to use inside visitor functions.

Example

`js
var Snapdragon = require('snapdragon');
var Compiler = Snapdragon.Compiler;
var compiler = new Compiler();
`

$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
compiler.set('foo', function(node) {
if (node.val !== 'foo') {
throw this.error('expected node.val to be "foo"', node);
}
});
`

$3

Concat the given string to compiler.output.

Params

* string {String}
* node {Object}: Optionally pass the node to use for position if source maps are enabled.
* returns {String}: returns the string

Example

`js
compiler.set('foo', function(node) {
this.emit(node.val, node);
});
`

$3

Emit an empty string to effectively "skip" the string for the given node, but still emit the position and node type.

Params

* {Object}: node

Example

`js
// example: do nothing for beginning-of-string
snapdragon.compiler.set('bos', compiler.noop);
`

$3

Define a non-enumberable property on the Compiler instance. This is useful in plugins, for exposing methods inside handlers.

Params

* key {String}: propery name
* val {any}: property value
* returns {Object}: Returns the Compiler instance for chaining.

Example

`js
compiler.define('customMethod', function() {
// do stuff
});
`

$3

Add a compiler fn for the given type. Compilers are called when the .compile method encounters a node of the given type to generate the output string.

Params

* type {String}
* fn {Function}

Example

`js
compiler
.set('comma', function(node) {
this.emit(',');
})
.set('dot', function(node) {
this.emit('.');
})
.set('slash', function(node) {
this.emit('/');
});
`

$3

Get the compiler of the given type.

Params

* type {String}

Example

`js
var fn = compiler.get('slash');
`

$3

Visit node using the registered compiler function associated with the node.type.

Params

* node {Object}
* returns {Object}: returns the node

Example

`js
compiler
.set('i', function(node) {
this.visit(node);
})
`

$3

Iterate over node.nodes, calling visit on each node.

Params

* node {Object}
* returns {Object}: returns the node

Example

`js
compiler
.set('i', function(node) {
utils.mapVisit(node);
})
`

$3

Compile the given AST and return a string. Iterates over ast.nodes with mapVisit.

Params

* ast {Object}
* options {Object}: Compiler options
* returns {Object}: returns the node

Example

`js
var ast = parser.parse('foo');
var str = compiler.compile(ast);
`

Snapdragon in the wild

A few of the libraries that use snapdragon:

* braces: Bash-like brace expansion, implemented in JavaScript. Safer than other brace expansion libs, with complete support… more | homepage
* breakdance: Breakdance is a node.js library for converting HTML to markdown. Highly pluggable, flexible and easy… more | homepage
* expand-brackets: Expand POSIX bracket expressions (character classes) in glob patterns. | homepage in glob patterns.")
* extglob: Extended glob support for JavaScript. Adds (almost) the expressive power of regular expressions to glob… more | homepage the expressive power of regular expressions to glob patterns.")
* micromatch: Glob matching for javascript/node.js. A drop-in replacement and faster alternative to minimatch and multimatch. | homepage
* nanomatch: Fast, minimal glob matcher for node.js. Similar to micromatch, minimatch and multimatch, but complete Bash… more | homepage")

History

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Breaking changes!

In an attempt to make snapdragon lighter, more versatile, and more pluggable, some major changes were made in this release.

* parser.capture was externalized to snapdragon-capture
* parser.capturePair was externalized to snapdragon-capture-set
* Nodes are now an instance of snapdragon-node

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Breaking changes!

Substantial breaking changes were made in v0.5.0! Most of these changes are part of a larger refactor that will be finished in 0.6.0, including the introduction of a Lexer class.

* Renderer was renamed to Compiler
* the .render method was renamed to .compile

About

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A few of the libraries that use snapdragon:

* snapdragon-capture-set: Plugin that adds a .captureSet() method to snapdragon, for matching and capturing substrings that have… more | .captureSet(" class="text-primary hover:underline" target="_blank" rel="noopener noreferrer">homepage method to snapdragon, for matching and capturing substrings that have an open and close`, like braces, brackets, etc")
* snapdragon-capture: Snapdragon plugin that adds a capture method to the parser instance. | homepage
* snapdragon-node: Snapdragon utility for creating a new AST node in custom code, such as plugins. | homepage
* snapdragon-util: Utilities for the snapdragon parser/compiler. | homepage

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| Commits | Contributor |
| --- | --- |
| 156 | jonschlinkert |
| 3 | doowb |
| 2 | danez |
| 1 | EdwardBetts |

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Jon Schlinkert

* LinkedIn Profile
* GitHub Profile
* Twitter Profile

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

*

_This file was generated by verb-generate-readme, v0.6.0, on March 20, 2018._