Introduction to Haskell

Haskell is a purely functional programming language. It is the language most commonly used to teach functional programming at A-Level. This lesson covers the essential Haskell syntax and features you need for your exam.

---

Why Haskell?

• Purely functional: No side effects, immutable data.
• Strongly typed: Every expression has a type checked at compile time.
• Lazy evaluation: Expressions are only computed when needed.
• Elegant syntax: Concise and mathematical.

---

Basic Syntax

Defining Functions

-- Simple function
double :: Int -> Int
double x = x * 2

-- Function with two parameters
add :: Int -> Int -> Int
add x y = x + y

-- Using the function
result = double 5      -- 10
sum = add 3 4          -- 7

The first line is the type signature (optional but recommended). The second line is the definition.

Type Signatures

-- Takes an Int, returns an Int
square :: Int -> Int
square x = x * x

-- Takes two Ints, returns an Int
multiply :: Int -> Int -> Int
multiply x y = x * y