loxx

Lox interpreter written in Rust (Lox is a scripting language created by Robert Nystrom for this book)

This repository contains two packages that corresponds to the following in the book

• loxi → jlox: a tree-walk interpreter (implementation complete)
• loxii → clox: a bytecode interpreter (not implemented yet)

Building

cargo build --bin loxi              # or loxii
cargo run --bin loxi -- --help      # opens help

Testing

The tests are performed using a python script

./test.py <interpreter> -c <chapter>

Use the -h flag to see how to use it.

Benchmarks

Running

You can run the benchmarks yourself using the python script

./benchmark.py <interpreter> <repeat>

Use the -h flag to see how to use it.

You can add other interpreters to the script by adding more enumeration to Interpreter class yourself. That is what I do to add and benchmark jlox below.

Result

The benchmarks are performed on an Intel Core i5-10500H machine with the frequency locked at 2.5GHz. Each benchmark are repeated 5 times and then averaged to get better result.

Tree-walk interpreter

	loxi	jlox	diff
binary_trees.lox	14.443941 s	9.880800 s	+46.18 %
equality.lox	9.941284 s	5.494600 s	+80.93 %
fib.lox	12.876985 s	6.060200 s	+112.48 %
instantiation.lox	3.923048 s	2.008800 s	+95.29 %
invocation.lox	4.071392 s	1.759000 s	+131.46 %
method_call.lox	2.020660 s	2.427200 s	-16.75 %
properties.lox	5.592753 s	6.464400 s	-13.48 %
string_equality.lox	3.659577 s	6.170000 s	-40.69 %
trees.lox	27.242201 s	32.009400 s	-14.89 %
zoo.lox	3.839772 s	6.017600 s	-36.20 %
zoo_batch.lox	10.007977 s	10.014200 s	-0.06 %

Bytecode interpreter

Not implemented yet

Extension

enable using cargo --features flag

• unicode: allows non-whitespace unicode as identifier.
• debug: adds a new statement, debug statement, that is similar to print but instead of printing to stdout, it prints to stderr.
• loxlox: provides the following functions that facilitate LoxLox.
  • getc(): gets char from stdin as number (currently not handling utf8 properly).
  • chr(ch): turns char code number into string (currently not handling utf8 properly, if they are encountered chr will return nil instead).
  • exit(status): exits with given status code.
  • print_error(msg): prints message to stderr (I modify it so it can print any kind of Lox Value).

TODO

These are from the challenges, I guess I'll add it as extension for the language and using cargo feature flag to enable it

• Add support for C-style block comments (/* ... */)
• Implement bitwise, shift, modulo, and conditional operators
• Add support for comma expressions (like in C)
• Add support for C-style conditional or "ternary" operator ?:
• Add option to raise a runtime error on division by zero
• Make it a runtime error to access a variable that has not been initialized or been assigned
• Add support for break and continue statements in a loop
• Add anonymous function support
• Extend the resolver to raise an error if a local variable is never used
• Implement static methods (use class to mark a method as static)
• Support "getter" and "setter" for class members (see the book on challenges section on classes chapter for the syntax)
• Add support for string interpolation

Other challenges but lower priority

Reasons for lower priority including but not limited to

• Implementing these as features will make programming more error-prone

• Allow ordering with different type (e.g. 3 < "pancake")
• For + operator, if either of the operand is a string, convert the other operand to string.