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Hoot Lang 🦉

Hoot is a general-purpose interpreted scripting language with an event loop. It's dynamically typed, with classes, inheritance, and closures. It's an implementation and extension of the Lox Programming language.

Hoot extends Lox by introducing an event loop for non-blocking I/O, more complex types (string, list, map), and a tiny standard library (web requests, file reading/writing, delay functions).

Why? I wrote it to learn more about interpreters! Crafting Interpreters is a useful handbook and I strongly recommend it.


Hoot uses (mostly-typed) Python 3.8 and no additional libraries.

Run the integration tests with python test_hoot.py. It should also pass mypy . with no issues.

Run a program with python hoot.py ./file.hoot.

Open the REPL with python hoot.py.



Example programs

Print the headers from a HTTP response.

fun print_headers(response) {
    print response.headers; // This is a map()
}

request("https://google.com", nil, nil, "GET", print_headers);

print "This message will print before print_headers is called.";

Delay a function.

fun make_logger(time) {
    fun logger () {
        print string(time) + "ms";
    }
    return logger;
}

delay(make_logger(0), 0); // 0ms delay

print "This message prints first because each task 'Runs-to-completion' a la JavaScript";

delay(make_logger(50), 50);
delay(make_logger(100), 100);

Everyone's favorite inefficient sorting algorithm.

fun bubble_sort(numbers) {
    for (let i = 0; i < numbers.length() - 1; i = i + 1) {
        for (let j = 0; j < numbers.length() - 1; j = j + 1) {
            if (numbers.at(j) > numbers.at(j + 1)) {
                let tmp = numbers.at(j);
                numbers.alter(j, numbers.at(j + 1));
                numbers.alter(j + 1, tmp);
            }
        }
    }
    return numbers;
}


let unordered_numbers = list(1, -1, 0.5, 12, 2);
print bubble_sort(unordered_numbers);

Read a file, print the length, append to it, then print the new length.

fun show_length(text) {
    print "File length: " + string(text.length());
}

fun show_original_length(text) {
    print "File length: " + string(text.length());
    
    fun callback() {
        read("examples/test_file.txt", show_length);
    }
    write("examples/test_file.txt", "a", "More text", callback);
}

read("examples/test_file.txt", show_original_length);

Language reference

Variables

let bool = true; // or `false`
let num = 0; // All numbers are floats and support `+`, `-`, `*`, `/`
let raw = "raw string"; // Strings support `+`

// Compare with `==`

Types

// string has `at(index)`, `alter(index, element)`, `length()`
let some_text = string("Hello, World!");
some_text.alter(12, "?");
print some_text; // "Hello, World?"

// list has `at(index)`, `alter(index, element)`, `length()`, `push(element)`, and `pop()`
let some_numbers = list(1, -1, 0.5, 12, 2);
print some_numbers.at(1); // -1

// map has `get(key)` and `set(key, element)`
let food_store = map();
food_store.set("burgers", 20);

Loops

for (let i = 0; i < 5; i = i + 1) {
    print i;
}

while (true) {
    print "Um.. let's quit this infinite loop.;
    break;
}

Functions/closures

fun make_adder(y) {
   fun adder(x) {
       return x + y;
   }
   return adder;
}

let my_adder = make_adder(10);
adder(5); // 15

Classes

// Lifted this example straight from chapter 13 of Crafting Interpreters
class Doughnut {
  init() {
    this.ending_mark = "!";
  }
  cook() {
    print "Fry until golden brown.";
  }
}

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

BostonCream().cook();

Standard library

See native.py for implementation details.


input(prompt) — Returns standard input.

read(file_path, callback) — reads a UTF-8 compatible file and passes it as the first argument to callback.

write(file_path, mode, data, callback) — writes data to a file. mode is the same as Python's open. Calls callback without passing any arguments.

clock() — UNIX seconds.

delay(milliseconds, callback) — like setTimeout in JavaScript.

request(url, data, headers, http_method, callback)callback is passed a response instance with the fields body and header which can be accessed via . dot.


License

MIT.

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🦉 A general-purpose interpreted scripting language with an event loop.

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