Gain insights into Haskell's functional programming by learning to write pure functions, use pattern matching, recursion, and Lists, define data types, and execute IO operations.

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Functional programming is a problem-solving paradigm that differs drastically from the imperative programming style of languages like C++ or Java. While functional programming principles have invaded most modern programming languages to some degree, there is no language that embraces this paradigm quite as Haskell does. As a result, Haskell code can reach a level of expressiveness, safety, and elegance that is difficult to achieve in other programming languages.

This course will introduce you to the core concepts of functional programming in Haskell. You will learn how to write pure functions using techniques such as pattern matching and recursion, and how to work with Haskell's powerful List data type. You will understand the basics of Haskell's powerful type system and define your own data types. Finally, you’ll learn how to perform IO operations the Haskell way. By the end of this course, you’ll have a new paradigm to add under your belt and you can start using functional programming in your own projects.

Learn Functional Programming in Haskell

In the next lessons, we will study the list datatype, the essential datatype of Haskell and functional programming in general. As lists are defined recursively themselves, they fit well to a language that uses recursion as its primary problem solving technique.

# The list datatype
A list is a linear data structure for a collection of elements. Each element points to the next element, except the last element, which points to a special `nil` value (the empty list). Here is a visualization of a list containing the three numbers `1, 2, 3`.

Just like tuples, we can make lists from any Haskell data type. List types are denoted using square brackets. A list of integers has the type `[Int]`, a list of doubles the type `[Double]`, and so on. To make list literals, we can simply enumerate values in square brackets. Here are some examples of lists:
```
ints :: [Int]
ints = [1, 2, 3]

empty :: [Int]
empty = []

functions :: [Int -> Int]
functions = [(+1), (*2)]

nested :: [[String]]
nested = [["hi"], ["how", "are", "you"], ["i'm", "fine"]]
```
As the examples show, we can make lists from any type, including function types and list types themselves (producing nested lists). Elements of one Haskell list must all have the same type. There can be no mixed lists of ints and doubles.

Lists in Haskell, like most types, are **immutable**, i.e., it is not possible to modify the values inside a list without creating a new list. But Haskell makes it easy to build new lists from existing ones.

Introduction

First Steps with Haskell

Techniques for Writing Functions

Working with Lists

Creating Data Types

Input and Output

Conclusion

Appendix

Introduction to Lists

The list datatype