Lox

Implementation of the Lox scripting language from a beautiful book Crafting Interpreters by Bob Nystrom.

Description

The WIP C++ implementation of Lox programming language. The main goals of this work is to utilize and practiсe modern C++20, especially such features as modules, ranges, smart pointers, etc.

The generation of AST's tree was done by the ast_generator tool, which was also written in C++ to produce modern C++20 code.

For now, I think of this work as a skeleton for my own language which will be targeted at writing microservices.

Supported features

• Statements
• Variables
• Print
• Control flow
• for and while loops
• Functions
• Resolving and binding variables
• Classes, properties, methods, this, init-constructors
• Inheritance, access to super class methods

Code example

fun fib(n) {
  if (n <= 1) return n;
  return fib(n - 2) + fib(n - 1);
}

  var a = clock();
  print fib(10);
  print "time: " + (clock() - a);

var a = "outer";
{
  var a = "inner";
  print a;
}
#prints "outer outer"

class Thing {
  getCallback() {
    fun localFunction() {
      print this;
    }

    return localFunction;
  }
}

var callback = Thing().getCallback();
callback();
#prints "Thing instance"

class Doughnut {
  cook() {
    print "Fry until golden brown.";
  }
}

class BostonCream < Doughnut {
  cook() {
    super.cook();
    print "Pipe full of custard and coat with chocolate.";
  }
}

BostonCream().cook();
#prints 
Fry until golden brown.
Pipe full of custard and coat with chocolate.

Optimizations

• Compare typeid in CheckAnyType instead of using std::any_cast and catching exceptions. It improves perfomance by 20 times in equality.lox benchmark.
• Cache strings in Environment, avoid unnecessary copies when compairing and accessing strings.

# Before optimization
>lox.exe equality.lox
loop
18.000000
elapsed
553.000000
equals
535.000000
# After
>lox.exe equality.lox
loop
7.000000
elapsed
14.000000
equals
7.000000

TODO

• Add string pool (same as in Java)