Updated: 2025-12-28 Sun 19:48

# haskellnotes

planted: 2024-12-12 last tended to: 2025-12-28

## Haskell Notes

### Introduction

Haskell is a purely functional programming language with strong static typing and lazyevaluation . It was named after the logician Haskell Curry. It is widely used in academia and industry for teaching and research as well as for writing industrial applications.

### Features of Haskell

- Purely Functional: Functions in Haskell are pure, meaning they don’t have side effects.
- Strong Static Typing: Types are checked at compile time, reducing runtime errors.
- Lazy Evaluation: Expressions are not evaluated until their values are needed.
- Type Inference: Haskell can automatically infer types, making the code more concise.
- Concise Syntax: Haskell’s syntax is clean and concise, making it easy to read and write.

### Getting Started with Haskell

- Installation: To get started with Haskell, you need to install the Glasgow Haskell Compiler (GHC). You can download it from Download
- Basic Syntax:
  - Comments: Single line comments start with `–`, and multi-line comments are enclosed within `{-` and `-}`.
  - Modules: Code is organized into modules, which can be imported using the `import` keyword.

### Basic Concepts

- Functions: Functions are first-class citizens in Haskell. A function definition looks like this:

      add :: Int -> Int -> Int
      add x y = x + y

  This defines a function add that takes two integers and returns their sum.

- Types and Type Classes: Types are a crucial part of Haskell. You define types using the `data` keyword, and type classes using the `class` keyword.

### Example

Here’s a simple example to demonstrate some basic features of Haskell:

    -- Define a new data type
    data Shape = Circle Float | Rectangle Float Float

    -- Define a function to calculate the area of a shape
    area :: Shape -> Float
    area (Circle r) = pi * r^2
    area (Rectangle l w) = l * w

    -- Example usage
    main = do
      let c = Circle 10
      let r = Rectangle 5 7
      print (area c)
      print (area r)

This example defines a new data type Shape with two constructors, Circle and Rectangle, and a function area that calculates the area of a shape.

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