evnx

a secure, peer-to-peer, decentralized projectional editor for building and evaluating Evan programs in real-time.

introduction

evnx is currently in development.

Having said that, you can see the final build in action here. Enjoy!

Documentation is coming soon

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evaluation of abstract nodes

The Evan language is implemented by means of an evaluator, which transforms JSON to JavaScript, and it is said to be a Lispy language in the context of JavaScript. (I'm hoping Meinte will explain this.)

It's in principle functional (evaluating the same piece of JSON will always lead to the same result), further, the evaluation is wired to happen incremental (using mobx), so the subsequent updates will only require a partial re-evaluation.

language

Evan's language constructs are structurally described in description.json file.

As an example, a binary operation definition looks like this when JSON is used as concrete syntax:

"binary operation": {
  "properties": {
    "operator": { "type": "string" },
    "left": { "type": "any" },
    "right": { "type": "any" }
  }
}

and here is an excerpt from an Evan program that uses this definition:

"body": {
  "$sType": "if-then-else",
  "condition": {
    "$sType": "binary operation",
    "operator": "<",
    "left": {
      "$sType": "value reference",
      "name": "n"
    },
    "right": 2
  }

You can optionally provide an external object table to the evaluator.

The evaluator will then transform those objects according to the following rules:

• Objects which have a string-valued property $sType are processed by their respective evaluation function.
  • This evaluation never throws but returns something sensible: either an issue object or undefined (which corresponds loosely to e.g. Scala's None).
  • The individual evaluation functions determine whether recursion into sub-values of sTyped objects happen.
• All other values (so also objects which are not "sTyped") are returned as-is.

External Objects is Evan's way of interfacing with things outside any Evan program on its own. It's nothing more than a map/dictionary of names to objects, which expose functions. Using the semantics type object-function invocation, you can interact with functions on these objects.

On type checking

• Evaluation does (some) type checking - which obviously happens at runtime.
• A separate type checker (once it exists) mimics the evaluator but computes and checks typing statically: this should help the developer beyond what's reasonable in terms of unit tests.
• Evan is not statically typed, but could at some point become optionally-typed.

CLI usage

evnx FILE OPTIONS

Options:

  --semantics    Print TypeScript semantics.
  -v, --version  Show meta-model version.
  -h, --help     Show this message.

development

Install dependencies and start the development server:

yarn
npm run test
npm run ide