Welcome to the world of Motoko, a modern and type-safe programming language designed specifically for building the next generation of distributed applications on the Internet Computer blockchain network. In this article, we will explore the key features of Motoko and its role in enabling developers to create secure and scalable applications on the Internet Computer. So, let’s dive in and discover the power of Motoko!

What is Motoko?

Motoko is a programming language that provides a familiar yet robust programming environment for developers to build decentralized applications on the Internet Computer. It is specifically designed to support the unique features of the Internet Computer and provide a seamless developer experience.

Motoko offers modern language features such as sound structural types, generics, variant types, and statically checked pattern matching. These features make it intuitive for developers familiar with JavaScript and other popular languages while providing the benefits of a type-safe environment.

Motoko and Canister Smart Contracts

Motoko is the language of choice for developing canister smart contracts on the Internet Computer. Canisters are autonomous objects that encapsulate their state and communicate with other canisters through asynchronous messages. In Motoko, a canister is represented as an actor, which consists of one or more public functions that can be invoked by other actors.

For example, let’s consider a simple Counter actor in Motoko:

actor Counter {
  var value = 0;

  public func inc() : async Nat {
    value += 1;
    return value;

In this example, the Counter actor has a single public function called inc() that increments the value by 1 and returns the updated value. Other actors can invoke this function to interact with the Counter actor.

Asynchronous Programming in Motoko

Motoko simplifies asynchronous programming by allowing developers to write code in a sequential style. Asynchronous messages in Motoko are function calls that return a future, and the await construct is used to suspend execution until a future has completed. This approach eliminates the need for explicit callback functions and avoids the callback hell commonly associated with asynchronous programming.

Let’s consider an example of an asynchronous Factorial actor in Motoko:

actor Factorial {
  var last = 1;

  public func next() : async Nat {
    last *= await Counter.inc();
    return last;

ignore await Factorial.next();
ignore await Factorial.next();
await Factorial.next();

In this example, the Factorial actor asynchronously invokes the inc() function of the Counter actor to calculate the factorial. The await keyword is used to suspend execution until the inc() function completes, ensuring the correct order of operations.

Familiar Syntax and Modern Features

Motoko is designed to be intuitive for developers familiar with JavaScript and other popular languages. It incorporates modern language features and best practices to enhance developer productivity and code maintainability.

One of the powerful features of Motoko is its support for generic types. Developers can define generic types that can be used with different data types, providing flexibility and code reusability. For example, we can define a generic Tree type in Motoko:

type Tree<T> = {
  #leaf : T;
  #branch : { left : Tree<T>; right : Tree<T> };

This Tree type can represent a hierarchical structure with leaf nodes and branch nodes. The use of generics allows us to create trees with different data types.

Motoko also supports statically checked pattern matching, which allows developers to handle different cases or patterns in a concise and type-safe manner. This feature enhances code readability and reduces the possibility of runtime errors. Here’s an example of pattern matching in Motoko:

func iterTree<T>(tree : Tree<T>, f : T -> ()) {
  switch (tree) {
    case (#leaf(x)) {
    case (#branch{left; right}) {
      iterTree(left, f);
      iterTree(right, f);

In this example, the iterTree function iterates over a tree and applies a function f to each leaf node. The pattern matching construct switch is used to handle different cases, making the code more expressive and readable.

Interoperability with Candid

Motoko provides seamless interoperability with other canisters and programming languages through Candid, a language-neutral interface description language. Candid allows canisters to communicate with each other and with external code by describing the messages and data types they support.

The Motoko compiler can automatically generate Candid interface descriptions for actors, enabling type-safe communication between canisters. This makes it easy for canisters implemented in different languages to interact with each other, as long as they support Candid.

For example, let’s consider the Counter actor we defined earlier. Its Candid interface would look like this:

service Counter : {
  inc : () -> (nat);

This interface describes the inc function of the Counter actor, specifying its argument and return types. By adhering to this interface, other canisters can seamlessly communicate with the Counter actor, regardless of the programming language they are implemented in.

Orthogonal Persistence in Motoko

Motoko provides built-in support for orthogonal persistence, which allows the state of a canister to be preserved indefinitely without the need for explicit saving and restoring of data. This feature ensures that the memory and other state of a canister remain intact even during upgrades or restarts.

For example, let’s consider a Registry actor that assigns sequential IDs to textual names. The state of the hash table in the Registry actor is preserved across calls, even when the actor is replicated across multiple Internet Computer nodes. Here’s an example of the Registry actor in Motoko:

import Text "mo:base/Text";
import Map "mo:base/HashMap";

actor Registry {
  let map = Map.HashMap<Text, Nat>(10, Text.equal, Text.hash);

  public func register(name : Text) : async () {
    switch (map.get(name)) {
      case null {
        map.put(name, map.size());
      case (?id) { };

  public func lookup(name : Text) : async ?Nat {

await Registry.register("hello");
(await Registry.lookup("hello"), await Registry.lookup("world"))

In this example, the Registry actor maintains a hash table to store names and their corresponding IDs. The state of the hash table is preserved across method invocations, ensuring data consistency and integrity.

Stability and Upgradability

Motoko provides features to ensure stability and upgradability of canister smart contracts. Developers can declare certain variables as stable, meaning their values are automatically preserved across canister upgrades. This feature allows canisters to evolve without losing their state or interrupting their services.

For example, let’s consider a Counter actor with a stable variable:

actor Counter {
  stable var value = 0;

  public func inc() : async Nat {
    value += 1;
    return value;

In this example, the value variable is declared as stable, which means its value will be preserved across canister upgrades. This allows counting to continue from the last value, even after an upgrade.

Motoko also provides user-definable upgrade hooks that run before and after an upgrade. These hooks allow developers to migrate arbitrary state to stable variables, facilitating smooth transitions during upgrades.

Motoko and the Future

Motoko is continuously evolving with each release of the IC SDK and ongoing updates to the Motoko compiler. The open-source nature of the Motoko compiler and tooling encourages contributions from the community, ensuring a vibrant and growing ecosystem.

As the Internet Computer blockchain network expands and more developers adopt Motoko, the language will play a crucial role in enabling the creation of secure, scalable, and decentralized applications. Its familiar syntax, modern features, and seamless interoperability with other canisters make it a powerful tool in the hands of developers.


Motoko is a powerful programming language designed specifically for building decentralized applications on the Internet Computer blockchain network. With its modern features, seamless interoperability, and support for orthogonal persistence, Motoko empowers developers to create secure and scalable applications.

As Motoko continues to evolve and mature, it will play a vital role in driving the adoption of the Internet Computer and revolutionizing the way we build and interact with decentralized applications. So, embrace Motoko and unlock the full potential of the Internet Computer!

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