DIY Lang
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 data types (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 very similar to 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
First, clone this repo.
git clone https://github.com/kvalle/diy-lang.git
cd diy-langThen, depending on your platform:
-
Mac: Install Python, either from the webpage or using
brew. Then runeasy_install noseto installnose, the test runner we'll be using.Optional: If you are familiar with virtualenv you might want to install
nosein a separate pyenv to keep everything tidy. -
Windows/Linux: Install Python, either from the webpage or your package manager of choice. Then install Pip. Finally, install
noselike this:pip install nose.Optional: If you are familiar with virtualenv you might want to install
nosein a separate pyenv to keep everything tidy. -
Vagrant: If you have Vagrant installed, an easy way to get going is to use the provided
Vagrantfile. Usevagrant upto boot the box, andvagrant sshto log in. The project folder is synced to/home/vagrant/diy-lang.
Test your setup
Once installed, run nosetests --stop see that everything is working properly. This will run the test suite, stopping at the first failure. Expect something like the following:
$ nosetests --stop
E
======================================================================
ERROR: TEST 1.1: Parsing a single symbol.
----------------------------------------------------------------------
Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/nose/case.py", line 197, in runTest
self.test(*self.arg)
File "/home/vagrant/diy-lang/tests/test_1_parsing.py", line 15, in test_parse_single_symbol
assert_equals('foo', parse('foo'))
File "/home/vagrant/diy-lang/diylang/parser.py", line 17, in parse
raise NotImplementedError("DIY")
NotImplementedError: DIY
----------------------------------------------------------------------
Ran 1 test in 0.034s
FAILED (errors=1)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. -
The Python cheat sheet in
python.mdUnless you're fluent in Python, there should be some helpful pointers in the Python cheat sheet. Also, if Python is very new to you, the Python tutorial might prove helpful.
-
Description of your language
Read a description of the language you are going to make in language.md.
Get started!
The workshop is split up into eight 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!