5. A worked example

A tiny to-do list, built up piece by piece. It uses classes, a list of instances, methods, a loop, and string building.

The task item

class Task:
    fn init(self, title):
        self.title = title
        self.done = false

    fn complete(self):
        self.done = true

    fn line(self):
        if self.done:
            return "[x] " + self.title
        else:
            return "[ ] " + self.title

The list

class TaskList:
    fn init(self):
        self.tasks = []

    fn add(self, title):
        self.tasks.push(Task(title))

    fn complete(self, index):
        self.tasks[index].complete()

    fn remaining(self):
        count = 0
        for task in self.tasks:
            if not task.done:
                count = count + 1
        return count

    fn show(self):
        for task in self.tasks:
            print(task.line())
        print(str(self.remaining()) + " left")

Using it

class Task:
    fn init(self, title):
        self.title = title
        self.done = false

    fn complete(self):
        self.done = true

    fn line(self):
        if self.done:
            return "[x] " + self.title
        else:
            return "[ ] " + self.title

class TaskList:
    fn init(self):
        self.tasks = []

    fn add(self, title):
        self.tasks.push(Task(title))

    fn complete(self, index):
        self.tasks[index].complete()

    fn remaining(self):
        count = 0
        for task in self.tasks:
            if not task.done:
                count = count + 1
        return count

    fn show(self):
        for task in self.tasks:
            print(task.line())
        print(str(self.remaining()) + " left")

todo = TaskList()
todo.add("write the guide")
todo.add("run the tests")
todo.add("ship it")
todo.complete(0)
todo.complete(1)
todo.show()
# => [x] write the guide
# => [x] run the tests
# => [ ] ship it
# => 1 left

Where to go next

• The specification for the exact rules.
• The decision records for why Korrin is shaped this way.
• crates/korrin/examples/ in the repository for more sample programs.