diff --git a/examples/aoc-2021/advent-day01.lox b/examples/aoc-2021/advent-day01.lox
new file mode 100644
index 0000000..f698f64
--- /dev/null
+++ b/examples/aoc-2021/advent-day01.lox
@@ -0,0 +1,72 @@
+var example = [199, 200, 208, 210, 200, 207, 240, 269, 260, 263];
+
+class WindowedArray {
+    init(array, size) {
+        this.array = array;
+        this.size = size;
+        this.current = 0;
+    }
+
+    next() {
+        if (this.current + this.size > this.array.length()) return Ok(nil);
+        var window = this.array.slice(this.current, this.current + this.size, 1);
+        this.current = this.current + 1;
+        return Ok(window);
+    }
+}
+
+class WindowedLineReader {
+    init(lineReader, size) {
+        this.lineReader = lineReader;
+        this.size = size;
+    }
+
+    next() {
+        if (this?.window == nil) {
+            this.window = Array(this.size);
+            for (var line, i = 0; i < this.size; i++) {
+                line = this.lineReader.readLine()!?;
+                this.window.set(i, line);
+            }
+            return Ok(this.window);
+        } else {
+            var line = this.lineReader.readLine()!?;
+            if (line == nil) {
+                return Ok(nil);
+            } else {
+                System.arraycopy(this.window, 1, this.window, 0, this.size - 1);
+                this.window.set(this.size - 1, line);
+                return Ok(this.window);
+            }
+        }
+    }
+}
+
+fun compute(windowed, convert) {
+    var window = windowed.next();
+    var previous = 0;
+    var count = 0;
+    while (window = windowed.next()!?) {
+       var sum = window.reduce(0, fun (a, b) = a + convert(b));
+       if (sum > previous) count++;
+       previous = sum;
+    }
+
+    return Ok(count);
+}
+
+fun part1Example(depths) = compute(WindowedArray(depths, 1), fun (x) = x);
+fun part2Example(depths) = compute(WindowedArray(depths, 3), fun (x) = x);
+
+fun windowed(file, size) =
+    WindowedLineReader(LineReader(BufferedInputStream(FileInputStream(file))), size);
+
+fun parseNumber(x) = String.toNumber(x).orElse(0);
+fun part1(file) = compute(windowed(file, 1), parseNumber);
+fun part2(file) = compute(windowed(file, 3), parseNumber);
+
+var file = File("examples/aoc-2021/advent-day01.txt");
+print part1Example(example); // expect: 7
+print part1(file); // expect: 1342
+print part2Example(example); // expect: 5
+print part2(file); // expect: 1378
diff --git a/examples/aoc-2021/advent-day01.txt b/examples/aoc-2021/advent-day01.txt
new file mode 100644
index 0000000..55921b9
--- /dev/null
+++ b/examples/aoc-2021/advent-day01.txt
@@ -0,0 +1,2000 @@
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\ No newline at end of file
diff --git a/examples/aoc-2021/advent-day02.lox b/examples/aoc-2021/advent-day02.lox
new file mode 100644
index 0000000..783a145
--- /dev/null
+++ b/examples/aoc-2021/advent-day02.lox
@@ -0,0 +1,95 @@
+class Submarine {
+    init() {
+        this.depth = 0;
+        this.horizontal = 0;
+    }
+
+    forward(n) {
+        this.horizontal = this.horizontal + n;
+        return this;
+    }
+
+    down(n) {
+        this.depth = this.depth + n;
+        return this;
+    }
+
+    up(n) {
+        this.depth = this.depth - n;
+        return this;
+    }
+
+    toString() {
+        return "Submarine(" + this.horizontal + ", " + this.depth + ")";
+    }
+}
+
+class SubmarineWithAim < Submarine {
+    init() {
+        super.init();
+        this.aim = 0;
+    }
+
+    forward(n) {
+        this.horizontal = this.horizontal + n;
+        this.depth = this.depth + this.aim * n;
+        return this;
+    }
+
+    down(n) {
+        this.aim = this.aim + n;
+        return this;
+    }
+
+    up(n) {
+        this.aim = this.aim - n;
+        return this;
+    }
+
+    toString() {
+        return "Submarine(" + this.horizontal + ", " + this.depth + ", " + this.aim + ")";
+    }
+}
+
+fun example(submarine) {
+    submarine
+        .forward(5)
+        .down(5)
+        .forward(8)
+        .up(3)
+        .down(8)
+        .forward(2);
+
+    return submarine.depth * submarine.horizontal;
+}
+
+
+fun parse(file) {
+    var commands = ArrayList();
+    var input = LineReader(BufferedInputStream(FileInputStream(file)));
+
+    var line;
+    while (line = input.readLine()!?) {
+        var (direction, value) = String.split(line, " ");
+        commands.add(Pair(direction, String.toNumber(value)!?));
+    }
+
+    return Ok(commands);
+}
+
+fun compute(commands, submarine) {
+    for (var (direction, value) in commands) {
+        if (direction == "forward") submarine.forward(value);
+        if (direction == "up") submarine.up(value);
+        if (direction == "down") submarine.down(value);
+    }
+
+    return submarine.depth * submarine.horizontal;
+}
+
+var input = parse(File("examples/aoc-2021/advent-day02.txt")).orFail();
+
+print example(Submarine()); // expect: 150
+print compute(input, Submarine()); // expect: 1480518
+print example(SubmarineWithAim()); // expect: 150
+print compute(input, SubmarineWithAim()); // expect: 1282809906
diff --git a/examples/aoc-2021/advent-day02.txt b/examples/aoc-2021/advent-day02.txt
new file mode 100644
index 0000000..9e714f9
--- /dev/null
+++ b/examples/aoc-2021/advent-day02.txt
@@ -0,0 +1,1000 @@
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+down 8
+down 6
+forward 3
+down 2
+forward 6
+up 2
+forward 6
+down 7
+up 4
+forward 1
+forward 4
+up 4
+forward 6
+forward 8
+down 7
+down 6
+up 7
+down 2
+down 4
+down 5
+forward 1
+up 4
+forward 8
+forward 6
+down 8
+up 5
+up 2
+up 9
+up 5
+forward 6
+down 4
+up 3
+down 8
+down 6
+down 2
+up 3
+up 5
+down 1
+forward 9
+up 8
+up 2
+down 3
+forward 6
+down 1
+forward 5
+down 3
+up 1
+up 2
+down 5
+down 7
+forward 8
+down 8
+up 9
+forward 3
+down 8
+down 8
+forward 1
+down 4
+down 4
+forward 3
+up 6
+down 3
+down 7
+down 7
+up 1
+forward 3
+forward 2
diff --git a/examples/aoc-2021/advent-day03.lox b/examples/aoc-2021/advent-day03.lox
new file mode 100644
index 0000000..2a871c6
--- /dev/null
+++ b/examples/aoc-2021/advent-day03.lox
@@ -0,0 +1,76 @@
+var example = [
+    "00100",
+    "11110",
+    "10110",
+    "10111",
+    "10101",
+    "01111",
+    "00111",
+    "11100",
+    "10000",
+    "11001",
+    "00010",
+    "01010",
+].toList();
+
+fun part1(input) {
+    var numberOfBits = String.length(input[0]);
+    input = input.map(fun(string) = Number.parseBinaryString(string).orNil());
+    var result = Array(numberOfBits);
+    result.fill(0);
+    for (var i = 0; i < input.length(); i++) {
+        for (var j = 0; j < numberOfBits; j++) {
+            result[numberOfBits - j - 1] = result[numberOfBits - j - 1] + ((input[i] >> j) & 1);
+        }
+    }
+
+    var gamma = result.map(fun(x) {
+       if (x > input.length() / 2) return 1; else return 0;
+    }).reduce("", fun (a, b) = a + b);
+
+    var epsilon = result.map(fun(x) {
+       if (x < input.length() / 2) return 1; else return 0;
+    }).reduce("", fun (a, b) = a + b);
+
+    return Number.parseBinaryString(gamma)!? * Number.parseBinaryString(epsilon)!?;
+}
+
+
+fun parse(file) {
+    var commands = ArrayList();
+    var input = LineReader(BufferedInputStream(FileInputStream(file)));
+
+    var line;
+    while (line = input.readLine()!?) {
+        commands.add(line);
+    }
+
+    return Ok(commands);
+}
+
+fun part2(input) {
+    var numberOfBits = String.length(input[0]);
+    fun find(mostFrequent) {
+        var copy = input.copy();
+        for (var i = 0; i < numberOfBits; i++) {
+            var zeros = copy.count(fun (row) = String.charAt(row, i).orNil() == "0");
+            var ones = copy.length() - zeros;
+            var toKeep;
+            if (zeros <= ones) {
+                if (mostFrequent) toKeep = "1"; else toKeep = "0";
+            } else {
+                if (mostFrequent) toKeep = "0"; else toKeep = "1";
+            }
+            copy.removeIf(fun (row) = String.charAt(row, i).orNil() != toKeep);
+            if (copy.length() == 1) return Number.parseBinaryString(copy.first())!?;
+        }
+    }
+
+    return find(true) * find(false);
+}
+
+var input = parse(File("examples/aoc-2021/advent-day03.txt")).orFail();
+print part1(example); // expect: 198
+print part1(input); // expect: 1025636
+print part2(example); // expect: 230
+print part2(input); // expect: 793873
diff --git a/examples/aoc-2021/advent-day03.txt b/examples/aoc-2021/advent-day03.txt
new file mode 100644
index 0000000..99c0fc4
--- /dev/null
+++ b/examples/aoc-2021/advent-day03.txt
@@ -0,0 +1,1000 @@
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diff --git a/examples/aoc-2021/advent-day04.example.txt b/examples/aoc-2021/advent-day04.example.txt
new file mode 100644
index 0000000..49d17bc
--- /dev/null
+++ b/examples/aoc-2021/advent-day04.example.txt
@@ -0,0 +1,19 @@
+7,4,9,5,11,17,23,2,0,14,21,24,10,16,13,6,15,25,12,22,18,20,8,19,3,26,1
+
+22 13 17 11  0
+ 8  2 23  4 24
+21  9 14 16  7
+ 6 10  3 18  5
+ 1 12 20 15 19
+
+ 3 15  0  2 22
+ 9 18 13 17  5
+19  8  7 25 23
+20 11 10 24  4
+14 21 16 12  6
+
+14 21 17 24  4
+10 16 15  9 19
+18  8 23 26 20
+22 11 13  6  5
+ 2  0 12  3  7
\ No newline at end of file
diff --git a/examples/aoc-2021/advent-day04.lox b/examples/aoc-2021/advent-day04.lox
new file mode 100644
index 0000000..ec720ca
--- /dev/null
+++ b/examples/aoc-2021/advent-day04.lox
@@ -0,0 +1,162 @@
+class Board {
+    init(size) {
+        this.board = Array(size);
+        for (var x in 0..(size - 1)) {
+            this.board.set(x, Row(size));
+        }
+    }
+
+    set(row, col, value) {
+        this.board.get(row).set(col, value);
+        return this;
+    }
+
+    mark(number) {
+        this.lastNumber = number;
+        for (var row in this.board) {
+            row.mark(number);
+        }
+    }
+
+    row(n) = this.board.get(n);
+
+    column(n) {
+        var col = Column(this.board.length());
+        for (var (i, row) in this.board.withIndex()) {
+            col[i] = row[n];
+        }
+        return col;
+    }
+
+    sum {
+        return this.board.reduce(0, fun(x, row) = x + row.sum);
+    }
+
+    isWon {
+        for (var row in this.board) {
+            if (row.isComplete) {
+               return true;
+            }
+        }
+        for (var col in 0..(this.board.length()-1)) {
+            if (this.column(col).isComplete) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    toString() {
+        var s = "";
+        for (var row in this.board) {
+            for (var cell in row) {
+                s = s + cell + " ";
+            }
+            s = s + "\n";
+        }
+        return s;
+    }
+}
+
+class BoardRowColumn < Array {
+    isComplete {
+        return this.reduce(this.get(0).isMarked, fun(a, b) = a and b.isMarked);
+    }
+
+    mark(number) {
+        this.filter(fun(cell) = cell.value == number).forEach(fun(cell) = cell.isMarked = true);
+    }
+
+    sum {
+        return this.filterNot(fun(cell) = cell.isMarked).reduce(0, fun(sum, cell) = sum + cell.value);
+    }
+}
+
+class Row < BoardRowColumn
+class Column < BoardRowColumn
+
+class Cell {
+    init(value) {
+        this.value = value;
+        this.isMarked = false;
+    }
+
+    mark() {
+        this.isMarked = true;
+    }
+
+    toString() {
+        var s = "";
+        if (this.isMarked) s = s + "[";
+        else s = s + " ";
+        if (this.value < 10) s = s + " ";
+        s = s + this.value;
+        if (this.isMarked) s = s + "]";
+        else s = s + " ";
+        return s;
+    }
+}
+
+fun parse(file) {
+    var boardSize = 5;
+    var lineReader = LineReader(FileInputStream(File(file)));
+
+    var numbers = String.split(lineReader.readLine()!?, ",").map(fun (s) = String.toNumber(s)!?);
+
+    var line;
+    var boards = ArrayList();
+    var board;
+    var row = 0;
+    while (line = lineReader.readLine()!?) {
+        if (String.length(line) == 0) {
+            if (board != nil) boards.add(board);
+            board = Board(boardSize);
+            row = 0;
+            continue;
+        }
+        var parts = String.split(line, " ").map(fun (x) = String.toNumber(x)!?);
+        for (var (col, value) in parts.withIndex()) {
+            board.set(row, col, Cell(value));
+        }
+        row++;
+    }
+
+    boards.add(board);
+
+    return Ok(Pair(numbers, boards));
+}
+
+
+fun part1(numbers, boards) {
+    for (var number in numbers) {
+        for (var board in boards) {
+            board.mark(number);
+            if (PRINT) print board;
+            if (board.isWon) return number * board.sum;
+        }
+    }
+}
+
+fun part2(numbers, boards) {
+    var won = ArrayList();
+    for (var number in numbers) {
+        for (var board in boards) {
+            board.mark(number);
+            if (board.isWon) {
+                if (PRINT) print board;
+                if (!won.contains(board)) won.add(board);
+                if (won.length() == boards.length()) {
+                    return won.last().sum * won.last().lastNumber;
+                }
+            }
+        }
+    }
+}
+
+var PRINT = System.arg(0) == "--printboards";
+var (numbers, boards) = parse("examples/aoc-2021/advent-day04.example.txt").orFail();
+print part1(numbers, boards); // expect: 4512
+print part2(numbers, boards); // expect: 1924
+var (numbers, boards) = parse("examples/aoc-2021/advent-day04.txt").orFail();
+print part1(numbers, boards); // expect: 71708
+print part2(numbers, boards); // expect: 34726
diff --git a/examples/aoc-2021/advent-day04.txt b/examples/aoc-2021/advent-day04.txt
new file mode 100644
index 0000000..1c64115
--- /dev/null
+++ b/examples/aoc-2021/advent-day04.txt
@@ -0,0 +1,601 @@
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