snapdragon

    0.12.1 • Public • Published

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    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 ❤️ and support.

    Table of Contents

    Details

    Install

    Install with npm:

    $ 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:

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

    Parse a string

    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()

    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

    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:

    { 
      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:

    { 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.

    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).

    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.

    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

    Parser

    Create a new Parser with the given input and options.

    Params

    • input {String}
    • options {Object}

    Example

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

    .error

    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

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

    .define

    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

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

    .node

    Create a new Node with the given val and type.

    Params

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

    Example

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

    .position

    Mark position and patch node.position.

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

    Example

    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]));
      }
    });

    .set

    Add parser type with the given visitor fn.

    Params

    • type {String}
    • fn {Function}

    Example

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

    .get

    Get parser type.

    Params

    • type {String}

    Example

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

    .push

    Push a node onto the stack for the given type.

    Params

    • type {String}
    • returns {Object} token

    Example

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

    .pop

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

    Params

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

    Example

    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;
      }
    });

    .isInside

    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

    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');
      }
    });

    .isType

    Return true if node is the given type.

    Params

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

    Example

    parser.isType(node, 'brace');

    .prev

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

    • returns {Object}

    Example

    var prev = this.prev();

    .prev

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

    Params

    • regex {RegExp}
    • returns {Object}

    Example

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

    Params

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

    Example

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

    Compiler

    Create a new Compiler with the given options.

    Params

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

    Example

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

    .error

    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

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

    .emit

    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

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

    .noop

    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

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

    .define

    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

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

    .set

    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

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

    .get

    Get the compiler of the given type.

    Params

    • type {String}

    Example

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

    .visit

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

    Params

    • node {Object}
    • returns {Object}: returns the node

    Example

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

    .mapVisit

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

    Params

    • node {Object}
    • returns {Object}: returns the node

    Example

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

    .compile

    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

    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
    • extglob: Extended glob support for JavaScript. Adds (almost) the expressive power of regular expressions to glob… more | homepage
    • 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

    v0.9.0

    Breaking changes!

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

    v0.5.0

    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

    Contributing

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

    Running Tests

    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
    Building docs

    (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

    A few of the libraries that use snapdragon:

    Contributors

    Commits Contributor
    156 jonschlinkert
    3 doowb
    2 danez
    1 EdwardBetts

    Author

    Jon Schlinkert

    License

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


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

    Install

    npm i snapdragon

    DownloadsWeekly Downloads

    13,896,545

    Version

    0.12.1

    License

    MIT

    Unpacked Size

    52 kB

    Total Files

    9

    Last publish

    Collaborators

    • jonschlinkert
    • doowb
    • danez