module test;

import stdlib/io;

fun main -> {
  io.println(foo() + 10);
}

trait Expr {
  visit<T>(visitor: Visitor<T>): T;
}

trait ExprVisitor<T> {
  visitString(string: String): T;
}

trait List<T : any> {
  size: int;
  get(index: int): T;
  set(index: int, value: T): void;
}

struct LinkedList<T : any> {
  head: T?;
  tail: LinkedList<T>?;

  init -> {
    self.head = null;
    self.tail = null;
  }
}

impl List<T> for LinkedList<T> {
  size -> {
    if self.head == null {
      return 0;
    }

    if self.tail == null {
      return 1;
    }

    return 1 + self.tail.size();
  }

  get(index) -> {
    if index == 0 {
      return self.head;
    }

    return self.tail.get(index - 1);
  }

  set(index, value) -> {
    if index == 0 {
      self.head = value;
      return;
    }

    if self.tail == null {
      raise StringError(
        "LinkedList<T>.set(...): index out of bounds",
      );
    }

    self.tail.set(index - 1, value,);
  }
}

fun foo -> "Hello World!";