Loxx

Master
Development

Loxx is a C++14 implementation of Bob Nystrom's toy language, Lox. Lox is syntatically similar to C and uses strong, dynamic types. For example:

var sum = 0;

for (var i = 0; i < 10; i = i + 1) {
  sum = sum + i;
}

print sum;

For more details on Lox's syntax, check out the description in Bob's book.

Compilation

Loxx uses no dependencies other than the C++14 standard library, so make sure you have a compiler that supports that standard. To run the build, you'll need CMake version 3 or greater. Once you've downloaded the source, in your terminal enter the root of the Loxx source tree and run:

mkdir build && cd build
cmake ..
make

Usage

Lox is an interpreted language. To run stuff interactively using a REPL, do

./loxx

Alternatively, execute source files like so

./loxx <your source filename>

Tests

Testing takes the form of a series of functional end-to-end tests that I effectively stole from Bob Nystrom's implemenations of Lox. To run the tests, use the python test-runner in the tests directory:

python tests/run_tests.py build/loxx

Benchmarks

Loxx is implemented as a bytecode virtual machine and performs reasonably well without having to micro-optimise the code and fine-tune compiler arguments. Here are some execution times (in seconds) from running each of the files in the benchmarks directory 20 times on an Intel i5-4300U (1.90 GHz) with a 3 MB L3 cache:

File	Min.	Mean	Median	Max.	Std. Dev.
binary_trees.lox	0.78	0.80	0.79	0.88	0.02
equality.lox	4.92	4.97	4.96	5.11	0.05
fib.lox	0.17	0.18	0.18	0.20	0.01
invocation.lox	0.60	0.62	0.61	0.79	0.04
method_call.lox	0.33	0.34	0.33	0.35	0.01
properties.lox	0.73	0.74	0.73	0.77	0.01
string_equality.lox	2.11	2.12	2.12	2.14	0.01

Compared to Clox, Bob Nystrom's C implementation, this isn't so bad:

File	Min.	Mean	Median	Max.	Std. Dev.
binary_trees.lox	0.58	0.59	0.59	0.60	0.01
equality.lox	5.32	5.35	5.33	5.51	0.05
fib.lox	0.12	0.12	0.12	0.13	0.00
invocation.lox	0.48	0.49	0.49	0.49	0.00
method_call.lox	0.27	0.27	0.27	0.28	0.00
properties.lox	0.66	0.66	0.66	0.67	0.00