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Interpreter for a subset of ECMA specification implemented on top of recursive descent parser


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Iterum (latin) means “again, a second time, repeatedly, once more, for the second time, anew,”. This is my another attempt to create a simple, but fully implemented interpreter for a subset of ECMA specification.

NOTE: This is an educational project, and it is not designed for use in production.


For a last few years I was passionate about compilers, languages and similar stuff. And I am still passionate about it.

However, all my knowledge was based on theoretical knowledge and not on a practical one. So, I’ve written an interpreter to fasten it.

Key Concepts

iterum itself is implemented on top of these key concepts:

  • Recursive descent parser with a look-ahead by one character;
  • Parser for an ECMA subset emits ESTree;
  • Interpreter is implemented on top of traverser for different AST nodes;

Getting Started

iterum is packed as an npm package, so you can easily run it with npx:

npx @ghaiklor/iterum --help

Create a file somewhere on your machine with an iterum code:

// hello-world.js
function helloWorld() {
    print "Hello, World";


If you want to take a look into AST generated from the file above:

npx @ghaiklor/iterum --print-ast hello-world.js

Otherwise, you can interpret it:

npx @ghaiklor/iterum --interpret hello-world.js


Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

Please make sure to update tests as appropriate.

How It Works

You can find rough explanation here.


MIT License