Pure Functional Programming in Dart

September 22, 2023

Functional programming has gained immense popularity in recent years due to its ability to write clean, maintainable, and bug-free code. While languages like Haskell, Scala, and even JavaScript have embraced functional programming concepts, you might be surprised to learn that Dart, the language developed by Google, also has its own functional programming library called Dartz developed by Björn Sperber.


The need for Functional Programming in Dart

Before we delve into Dartz and functional programming, it’s essential to understand why one might consider using functional programming in Dart.

Dart is primarily known as the language used for developing mobile and web applications with the Flutter framework. While Dart is a versatile language, it wasn’t initially designed with functional programming in mind. Functional programming is characterized by immutability, pure functions, and referential transparency, which can be challenging to achieve in a language like Dart.

However, there are compelling reasons to explore functional programming in Dart.


Improved Code Quality

Functional programming encourages writing code that is easier to reason about, test, and maintain. It minimizes side effects and promotes pure functions, which lead to more predictable behavior.


Enhanced Testability

Functional code tends to be more testable by design. This is particularly valuable when developing complex applications, as it makes it easier to write unit tests and ensure correctness.



Functional programming promotes the creation of reusable, composable functions and data structures. This can lead to a more modular and extensible codebase.


Expressive Abstractions

Functional programming introduces powerful abstractions like monads, functors, and monoids, which can help clarify code and improve its intent.


Introducing Dartz

Dartz is a functional programming library for Dart that provides the building blocks for writing functional code in Dart applications. While DartZed may not be as mature or extensive as similar libraries in languages like Haskell or Scala, it offers a valuable set of tools for developers who want to explore functional programming in Dart.

Some of the key components of Dartz include:

  • Option and either: These types help manage the presence or absence of values and handle exceptions more gracefully.
  • Immutable collections: Dartz provides immutable collections like `IList` and `IMap`, which are essential for functional programming.
  • Type class instances: Although Dart lacks higher-kinded types, Dartz attempts to encode fundamental type classes like monoids and functors to enhance code clarity.
  • Monadic transformer stacking: To handle complex monad stacks, Dartz includes the `Evaluation` monad stack, which combines reader, writer, state, either, and asynchronous support.
  • Free monads: Free monads are essential for modeling domain-specific languages and are available in Dartz.
  • Functional streaming: While considered experimental, Dartz also provides a functional streaming module.
  • Bridge code: Dartz includes utilities for integrating with Dart’s built-in types and standard library.
  • Type class instances: Dartz provides type class instances for many built-in types, enhancing their functional capabilities.


Exploring Dartz in action

Björn Sperber has done a presentation where he demo Dartz, and builds a simple menu and a shopping list list.



Functional programming has found its way into the Dart programming language through libraries like Dartz. While Dart may not be synonymous with functional programming, it offers a unique opportunity to explore functional concepts in the context of mobile and web development.

Björn Sperber’s presentation on “Pure Functional Programming in Dart” sheds light on the challenges and benefits of using Dartz to embrace functional programming principles. Whether you’re building Flutter applications or exploring Dart for other purposes, functional programming can lead to cleaner, more testable, and more reusable code.

So, if you’re a Dart enthusiast looking to level up your programming skills, consider taking a journey into the world of functional programming with Dartz. It might just open up new possibilities and make your Dart code more elegant and robust.


Additional resources

Check out the Ada Beat Functional Programming blog for more topics, including functional programming principles, summaries of MeetUps, language specific articles, and much more. Whether you’re interested in functional programming theory or practical application, we have something for everyone.