Kaffee

A Rust-powered "JEsque" programming language

What?

Kaffee is a toy project of mine to create a tokeniser, parser, lexer, interpretter and garbage collector in Rust.

Why?

As well as being a fun side-project as my first real Rust program, my overall goal is to create a language similar to JavaScript, but without the parts which frustrate and baffle many people who don't use it regularly.

For example, the type system does not include undefined or NaN, accessing a non-existent key in an object throws, as does dividing by zero, rather than breaking obscure parts of your code by sending these unexpected values through it silently.

Features

• Objects - Object literals, computed property access, etc.
• No hoisted variables - Variables are exclusively block-scoped
• More predictable boolean coercion - null is the only value which is falsy (besides false)
• Tracing garbage collector
• Rust/Python-like if syntax
• Rust-like fn syntax

Examples

Hello world:

println("Hello, world!")

Fizzbuzz:

for (let i = 1; i <= 100; i++) {
  let out = ""
  if i % 3 == 0 out = "Fizz"
  if i % 5 == 0 out += "Buzz"
  if out == "" out = i
  println(out)
}

Note that most of the syntax in the for statement is optional, to make the language feel more comfortable. Kaffee doesn't need the brackets, semi-colons, etc. to know what you mean.

for let i = 0 i < 5 i++ println(i)

Recursive factorial:

fn factorial(n) {
  if n < 2 return n
  return n * factorial(n - 1)
}
println(factorial(5))

Objects:

Objects can contain functions, functions can return objects, new keys can be created with assignment.

fn myFunc () {
  return {
    subFunc: fn () {
      println("I'm a first-class function")
    }
  }
}

const person = {
  name: "Adam",
  myFunc
}

person.age = 17
person.myFunc().subFunc()