parser

A configurable parser to parse whatever you want

npm install parser
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Synopsis

This module is basically a class that provides general mechanisms for parsing strings. It works with my tokenizer although it can be used with pretty much anything emitting tokens the same way. The parser works with a queue of functions. For each token the next function in the queue is called.

write you own parser

tokenizer

Only one thing is required for the parser to work : a tokenizer. These concepts are very different and that is why they are implemented separately. The easiest solution is to use my tokenizer

parser

The default behaviour upon receiving a new token is ignoring it. It prints a warning when reaching EOF with the number of tokens that have been ignored. However this is probably not what you want to do!

In order to parse what you need to parse you have to provide the parser with the functions which will be called for each token. Let's call these functions 'handlers'. This can be achieved through configuration of the basic parser or through inheritance.

var Parser = require('parser');
var util = require('util');
var MyTokenizer = require('./MyTokenizer');

function MyParser() {
    // MyTokenizer is the tokenizer we configured
    // but it's not the subject of this module
    Parser.apply(this, new MyTokenizer());

    // override the default behaviour
    this.defaultHandler(this.default);

    // specify the function that will be called on the first token
    this.initialHander(this.initial);
}
util.inherits(MyParser, Parser);

/**
 * Of course you will have to define these functions somewhere
 */

This is very theoretic but you can have a look at what is in the example folder

Handlers

Handlers are just javascript functions accepting the following arguments:

  • token the actual token emitted by the tokenizer
  • type the type of this token (i.e. 'number', 'whitespace', 'word')
  • next a function to specify what needs to be called on the next token(s)

the next function takes a random number of handlers which will be pushed in front of the handlers queue (they will be next!). returning true from a handler causes the same token to be reemitted to the next handler.

This allows you to define handlers doing some kind of "sniffing" if you find yourself in a state in which you cannot determine what will come next. This kind of handlers expand themselves to a greater number of handlers that will effectively parse the following tokens. They do that by adding a few handlers to the queue with next and returning true to notify the parser that the token should be reemitted.

Handlers utilities

there are a few handlers factories provided by this module.

  • checkType(type) returns a handler that only checks the type of the token without doing anything so the same token is pass down to the next handler
  • expect(type) returns a handler that checks for the specified type and consumes the token
  • list(separator, element, end) returns a handler expanding to the handlers needed to parse a list of elements able to be parsed by element and separated by tokens of type separator. The list should end by a token of type end

project

TODOs

  • more robustness / better error handling
  • features requests
  • Support for asynchronous handlers
  • allow for complex separator an ending tokens for handler utilities

Features requests / bugs

If you'd like the parser to do something that it doesn't do or want to report a bug please use the github issue tracker on github

fork / patches / pull requests

You are very welcome to send patches or pull requests

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