Awesome

Pykaleidoscope

This Python project implements the Kaleidoscope toy language as described on the LLVM tutorial (up to the part and including Mutable Variables). For that purpose, it uses the llvmlite python library. That project code is heavily inspired from the simpler pykaleidoscope project of eliben. The main differences are the followings:

• The code is separated in logical modules (lexer, parser, codegenerator, etc.) instead of being all in a single file.
• Only the final tutorial step is presented, so there is no step files (1, 2, 3, 4, etc.)
• A simple command line REPL has been added to drive code interpretation, verify and test programs.
• Code files can be runned.
• A basic language standard functions and operators library is automatically loaded before execution.
• The language has been modified a little bit...
  • For loops increments need to be specified like this x + 1 instead of 1. This permits more expressive looping steps like iterating through the first 10 powers of 2 like this: for x = 1, x < 1024, x * 2 in expr.
  • The for loop condition is checked before body execution and not after, so there is no extra run. Hence the for loop behaves just like expected in any other programming language.
  • No semicolon ; is needed as a separator between instructions.
  • No comma , is needed to separate variables in a var instruction.

Motivation

I made this project as a way to teach myself the basics of LLVM, and made it public as a way to show others what can be done because there is not much LLVM simple stuff out there on the Internet. And the official LLVM tutorial, being written in C++, is not that easy to follow if your are not acquainted with that language.

Installation and examples

Python needs to be installed first if not already available on your system. I used version 3.5 with miniconda3 under Windows, but any OS should work just fine.

Then install the llvmlite Python package:

conda install llvmlite

There is no need to install LLVM on its own since the llvmlite install includes a subset of LLVM which is just fine for our purposes.

Then download the pykaleidoscope code in its own folder, open a command line in that folder and execute the kal.py file to launch the kaleidoscope jit-compiler/interpreter. A prompt will show up like this K>. At the prompt, type test, to run the tests and make sure everything works well. Then, to get in touch with the power of this very simple language, run the .mandelbrot.kal program by simply entering its name after the prompt. The pykaleidoscope REPL will load the program, compile it in memory and then run it, which will show a very basic Mandelbrot set. Well, I am not the author of that Mandelbrot stuff, since it comes from the original LLVM tutorial, but it is indeed quite a surprising realisation for such a simple language.

K> test
... unit tests stuff showing up ...
K> .mandelbrot.kal
... mandelbrot set showing up ...
K> 2 + 3     # or any other kaleidoscope code
5.0
K> .functions
... shows available functions ...
K> exit
... return to command line from here ...

Limitations

As is, this language and interpreter has many limitations.

• A function cannot be defined twice, so running the same script file most likely will generate some error, aborting the script. To alleviate that, reset the engine with the command .reset before rerunning the script.
• Some error messages are very uninformative, especially for scripts, since the lexer does not produce line and position numbering for tokens.
• There are no global variables, only locals.
• The only I/O function is putchard(ascii_code), which outputs a single character on screen given its ascii code.
• The only type is double, so there is no int, char or string.
• If an external function is declared but called while not available, the program will crash with an error message but no exception. I guess Python is not able to catch this deep below LLVM error and to trigger an Exception.

History

Version 0.1.3

• The program can now reload itself from the prompt using the .reload command. All the changes to the code base will be taken into account.

Version 0.1.2

• Assignment operator = is now right associative, so x = y = 9 now works just fine, assigning both x and y to 9.

Version 0.1.1

• Added C functions from math.h at engine startup.
• Added .functions REPL command to list all available functions.
• Added .version REPL command to get general info.

Version 0.1.0

• Initial minimalistic working version.

Enjoy!