breuleux/earl-grey

Programming language compiling to JavaScript

Source code at GitHub http://breuleux.github.io/earl-grey/

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  "language": "JavaScript",
  "name": "earl-grey",
  "pushedAt": "2017-08-14T01:58:56Z",
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  "topics": [
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  "updatedAt": "2025-08-25T16:27:57Z",
  "url": "https://github.com/breuleux/earl-grey"
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Earl Grey

Earl Grey (website) is a new language that compiles to JavaScript (ES6). Here’s a quick rundown of its amazing features:

Python-like syntax
Fully compatible with the node.js ecosystem
Generators and async/await (no callback hell!)
Powerful, deeply integrated pattern matching
- Used for assignment, function declaration, looping, exceptions…
A DOM-building DSL with customizable behavior
A very powerful hygienic macro system!
- Define your own control structures or DSLs
- Macros integrate seamlessly with the language
- Macro libraries! Test with earl-mocha, build with earl-gulp, make dynamic pages with earl-react, etc.
And much more!

Resources

Examples

Counting all words in a block of test. Note that count-words is a variable name, not a subtraction (it is equivalent to the name countWords, if that’s the notation you prefer).

count-words(text) =
   counts = new Map()
   words = text.split(R"\W+")
   words each word ->
      current-count = counts.get(word) or 0
      counts.set(word, current-count + 1)
   consume(counts.entries()).sort(compare) where
      compare({w1, c1}, {w2, c2}) = c2 - c1

{x, y, ...} is the notation for arrays in Earl Grey. Objects are denoted {field = value, field2 = value2, ...}

Generators: the following defines a generator for the Fibonacci sequence and then prints all the even Fibonacci numbers less than 100. It shows off a little bit of everything:

gen fib() =
   var {a, b} = {0, 1}
   while true:
      yield a
      {a, b} = {b, a + b}

fib() each
   > 100 ->
      break
   n when n mod 2 == 0 ->
      print n

The each operator accepts multiple clauses, which makes it especially easy to work on heterogenous arrays.

Asynchronous: EG has async and await keywords to facilitate asynchronous programming, all based on Promises. Existing callback-based functionality can be converted to Promises using promisify:

require: request
g = promisify(request.get)

async getXKCD(n = "") =
   response = await g('http://xkcd.com/{n}/info.0.json')
   JSON.parse(response.body)

async:
   requests = await all 1..10 each i -> getXKCD(i)
   requests each req -> print req.alt

Classes:

class Person:
   constructor(name, age) =
      @name = name
      @age = age
   advance-inexorably-towards-death(n > 0 = 1) =
      @age += n
   say-name() =
      print 'Hello! My name is {@name}!'

alice = Person("alice", 25)

Pattern matching acts like a better switch or case statement. It can match values, types, extract values from arrays or objects, etc.

match thing:
   0 ->
      print "The thing is zero"
   < 0 ->
      print "The thing is negative"
   R"hello (.*)"? x ->
      ;; note: R"..." is a regular expression
      print 'The thing is saying hello'
   Number? x or String? x ->
      print "The thing is a number or a string"
   {x, y, z} ->
      print 'The thing is an array of three things, {x}, {y} and {z}'
   {=> name} ->
      print 'The thing has a "name" field'
   else ->
      print "I don't know what the thing is!"