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DIY Lisp

batteries included, some assembly required

In this tutorial/workshop we'll be implementing our own little language, more or less from scratch.

By the end of the tutorial you will be the proud author of a programming language, and will hopefully better understand how programming languages work on a fundamental level.

What we will be making

We will make a relatively simple, but neat language. We aim for the following features:

  • A handful of datatypes (integers, booleans and symbols)
  • Variables
  • First class functions with lexical scoping
  • That nice homemade quality feeling

We will not have:

  • A proper type system
  • Error handling
  • Good performance
  • And much, much more

The language should be able to interpret the following code by the time we are done:

(define fact 
    ;; Factorial function
    (lambda (n) 
        (if (eq n 0) 
            1 ; Factorial of 0 is 1
            (* n (fact (- n 1))))))

;; When parsing the file, the last statement is returned
(fact 5)

The syntax is that of the languages in the Lisp family. If you find the example unfamiliar, you might want to have a look at a more detailed description of the language.

Prerequisites

Before we get started, make sure you have installed Ruby

Then install Minitest, the Ruby test framework we'll be using.

gem install minitest

Finally, clone this repo, and you're ready to go!

git clone https://github.com/McFreely/ruby-lisp.git

A few tips

Take the time to consider the following points before we get going:

  • Keep things simple

    Don't make things more complicated than they need to be. The tests should hopefully guide you every step of the way.

  • Read the test descriptions

    Each test has a small text describing what you are going to implement and why. Reading these should make things easier, and you might end up learning more.

  • Use the provided functions

    Some of the more boring details are already taken care of. Take the time to look at the functions provided in parser.py, and the various imports in files where you need to do some work.

  • Description of your language

    Unfamiliar with Lisp? Read a description of the language you are going to make in language.md.

Get started!

The workshop is split up into seven parts. Each consist of an introduction, and a bunch of unit tests which it is your task to make run. When all the tests run, you'll have implemented that part of the language.

Have fun!

This project is a port of diy-lisp in from Python to Ruby. Go check the original on Kjetil Valle Repo

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A port of diy-lisp, to implement a lisp in ruby step by step

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