kukel

kukel

A simple programming language, just for fun: Kukel, with C-like syntax, classes, closures and exceptions, compiled to bytecode for a small stack machine written in Go.

// shapes.kkl
class Shape { name; Shape(name); area(); describe(); }
Shape::Shape(name) { this->name = name; }
Shape::describe() { return name + ": " + str(area()); }

class Circle : Shape { r; Circle(r); area(); }
Circle::Circle(r) { Shape::Shape("circle"); this->r = r; }
Circle::area() { return 3.14159 * r * r; }

class Square : Shape { side; Square(side); area(); }
Square::Square(side) { Shape::Shape("square"); this->side = side; }
Square::area() { return side * side; }

main(args) {
    local shapes = [new Circle(1), new Square(3), new Circle(2)];
    sort(shapes, fn(a, b) { return a->area() < b->area(); });
    for (local s in shapes) println(s->describe());

    try {
        println(shapes[5]);
    } catch (e) {
        println("caught", e->kind + ":", e->message);
    }
}

$ kukel run shapes.kkl
circle: 3.14159
square: 9
circle: 12.56636
caught RangeError: index 5 out of range for vector of length 3

What is in the language

• ints (64-bit, wrapping), floats, strings (bytes), booleans, nil
• vectors and maps (insertion order) with literals, indexing and for-each
• functions with default and rest parameters, spread arguments (f(v..))
• function literals (fn (x) { ... }) that capture variables by reference
• classes with single inheritance, constructors, static members, virtual member functions and bound methods (p->method)
• try/catch/finally, throw, and runtime errors as Error objects
• switch with fall-through, labelled break/continue
• 57 built-in functions (strings, collections, math, files, ...)

The full description is in docs/reference.md; the grammar is in syntax.ebnf (and as a Lark grammar in syntax.lark). How programs are compiled and run (the virtual machine, every instruction, the .kkc format) is specified in docs/vm.md.

Installing

With Go 1.22 or newer:

go install github.com/maarten-boot/kukel/cmd/kukel@latest

or from a clone:

make            # vet, test and build bin/kukel
make install    # install kukel into $(go env GOPATH)/bin

Using it

tests/run has example programs: FizzBuzz, a JSON parser, word counting, closures, exceptions and more. Each comes with its expected output.

How it works

source ──lexer──▶ tokens ──parser──▶ syntax tree ──compiler──▶ bytecode ──VM──▶ run
                                                                  │
                                                       .kkc file ◀┘ (build / exec)

TODO.md holds the plan the interpreter was built from, with all design decisions (Q1–Q34). Ideas for later are in docs/future.md.

Development

License

MIT, see LICENSE.