Tagged Human JSON (THJSON) Parser

There is a git repository here:

Sooner or later, all developers try to store some sort of structured data to configure their applications in some way. Perhaps it’s simple configuration files pointing to databases, perhaps it’s data files for game entities, perhaps it’s i18n translation files.

There are a million data formats that you might consider using. Probably the five most popular formats are:

  • INI files
  • XML files
  • YAML files
  • JSON files
  • HJSON files

Each has advantages and disadvantages for various use cases. But what if you wanted a format that comfortably handled ALL use cases?

INI files can’t handle any kind of nested structure. The only concept is blocks of key=value pairs where each value must fit on a single line. It allows comments
XML files are huge and verbose, and the syntax is unnecessarily pernickety for human beings to write. It is well-specified but bloated with features that can tie you in knots. It does cope with arbitrarily complex data well, though this can be its undoing. You can comment it but often in a restricted manner. But seriously, it’s a faff and everybody hates typing it.
YAML is a hideous format designed by devils. It contains a kitchen sink, manufactured in Hell. It too is pernickety with syntax requiring actually properly formatted whitespace, which is a sure sign of Satan’s work. We shall not speak of it again.
JSON files are very simple to parse for a computer. Unfortunately the syntax is also unnecessarily pernickety for human beings to type and hurts the eyes somewhat with all the unnecessary quotes and commas, and the only data structures it can directly deal with are primitive values, arrays, and maps. What’s worse is it can’t have comments in it, which renders it pretty useless for humans.
HJSON is getting close to perfection. You can read all about HJSON at https://hjson.org and even try it out in the browser. HJSON removes all the unnecessary syntactical cruft from JSON, making mostly everything optional; and it adds a few new features such as comments in every style imaginable and multiline strings. HJSON is easily converted into JSON for feeding to other APIs. Unfortunately HJSON has one major flaw, which is that it cannot handle the concept of “classes”. We can have null, numbers, booleans, strings, arrays, and maps, all nested arbitrarily… but we cannot declare a map to be a structured type, or “class”. This is a big pain in the arse if you are dealing with modern OOP languages, because they deal a whole lot in classes.


THJSON looks almost exactly like HJSON - it is in fact a superset of HJSON, which itself is a superset of JSON. The extra bit is the addition of a class name before a map (maps are objects that are enclosed in {} parentheses):

left_hand: sword {
    damage: 3
    weight: 1kg

Essentially any value that is parsed as a string that then starts to define a map with the opening curly brace, becomes instead a class, of a type name which is the string so far. No whitespace is allowed in the type name unless it is quoted.

We can do the same for arrays - define a class type for the array. We don’t actually check that the elements themselves conform to the type - indeed we don’t do anything with the class type name other than pass it to the stream listener:

inventory: item [sword, axe, shoes, tea, "no tea"]

The streaming parser presented here is pretty high-speed and generates almost no garbage. In fact it only even has to allocate any objects if you start using escapes in string data. It otherwise accepts UTF-8 data as a byte[] array, which can be in either Windows, *nix or Mac line ending format, and will fire off a streamed sequence of events to a listener pointing at subsections of the input array as tokens.

In the git repository there’s an example listener that converts the stream of tokens into a Google Json object. Classes are converted into JSON objects by simply creating a property called “class”:


Lists create an object of class “array” with a property “elements”:

            "no tea"

That’s not the “definitive” way to do it but it’s what the example listener does. That’s about it really.

Note that there isn’t a complementary THJSON writer in this repository… the stream reader presented here is “lossy” in that it discards comments and whitespace. It probably wouldn’t be too hard to create a writer. Maybe that’s next.

Cas :slight_smile:

I cannot stand git. I do not understand git. Whatever UI comes with Eclipse these days serves only to make it impossibly complex. I have no idea how to use it and whenever I try it literally refuses to do anything, at all. In the end I resorted to dragging and dropping my src folder onto the github webpage to add files. How they could make something so simple as source control so impossible in Eclipse is a mystery. Anyway… don’t ask me to do anything with this repo, because I can’t figure it out.