Learn HASKELL with Real Code Examples

Haskell is purely functional - everything is an expression without mutable state.

It features strong static typing powered by an advanced type system.

Used for reliable backend systems, research, compilers, finance, and high-assurance software.

Purity and referential transparency

Static strong typing

Lazy evaluation

Typeclasses for polymorphism

Algebraic data types

Pattern matching

Immutability

Expressions over statements

Functions and purity

Type system & typeclasses

Pattern matching

Monads & functors

src/ modules

package.yaml or cabal file

stack.yaml

tests/ folder

Main.hs entry point

Create project via Stack or Cabal init

Define modules

Write pure functions

Add dependencies

Compile using GHC

Run executable

Beginner: simple pure functions

Intermediate: typeclasses, modules

Advanced: monads, concurrency

Expert: compilers, GADTs, STM

Safer and more mathematical than Python

More advanced type system than Java

Stronger safety guarantees than JavaScript

Slower ecosystem growth than Rust

1990 – Haskell 1.0

1998 – Haskell 98 standard

2010 – Haskell 2010

2014–2025 – GHC modern advancements

Lazy evaluation: compute when needed

Typeclass: polymorphism mechanism

Monad: controlled effects

GADT: advanced type form

Pure function: no side effects