clox

Compiler for the lox language. C implementation of Crafting Interpreters by Robert Nystrom.

Build & run

$ cmake --workflow --preset default
$ build/clox example/hello.lox

clox compiler

clox is a single-pass compiler for the lox language written in C. It internally compiles lox to bytecode that is interpreted by a stack virtual machine (VM). Right now the compiled bytecode is not exportable.

Here are some nice internal features:

• clox uses a mark-sweep garbage collector (GC). Accessible objects are recursively descended and marked as used. Then the GC frees all unused objects.
• All strings are interned. The VM stores only one immutable copy of every string and all string usages reference those. It provides memory efficiency and fast string comparison. Unused strings are freed by the garbage collector.
• Closures reference non-local variables with upvalues, ie. references on their stack location. If stack is poped, upvalues fetch and locally store (close) their referenced variable.

Lox language

Lox is a toy language designed by Robert Nystrom for its Crafting Interpreters book. It is high level, dynamically typed, automatic memory managed, object oriented.

Hello World

// First example
print "Hello World";

Dynamic typing

var name = "Bob";
var greetings = "Hi";

print greetings + " " + name;

Functions & control flow

fun factorial(n) {
    var res = 1;
    for (var i = 2; i <= n; i = i+1) {
        res = res * i;
    }
    return res;
}

fun factorial_rec(n) {
    if (n < 2) {
        return 1;
    } else {
        return factorial_rec(n-1) * n;
    }
}

print factorial(6);
print factorial_rec(7);

Closures

fun log(prefix) {
    fun pprint(message) {
        print "[" + prefix + "] " + message;
    }
    return pprint;
}

var debug = log("+");
debug("Start exec");  // [+] Start exec

Classes and Inheritance

class Rect {
    init(x, y) {
        this.x = x;
        this.y = y;
    }
    area() { return this.x * this.y; }
    str() { return "Rectangle"; }
}

class ColoredRect < Rect {
    init(x, y, color) {
        super.init(x, y);
        this.color = color;
    }
    str() { return super.str() + " in " + this.color; }
}

var r = ColoredRect(3, 4, "yellow");
print r.area();  // 12
print r.str();  // Rectangle in yellow