.verb.md

Created by [jonschlinkert]({%= author.url %}) 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('{%= name %}');
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

Parse

{%= apidocs("lib/parser.js") %}

Compile

{%= apidocs("lib/compiler.js") %}

Snapdragon in the wild

{%= verb.related.description %} {%= related(verb.related.implementations) %}

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.

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

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