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:ID:       347d2663-515b-4d9a-9ee9-7706ee86a845
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#+title: haskell_notes
#+filetags: :index:notes:haskell:coding:


* Haskell Notes
** Introduction
Haskell is a purely functional programming language with strong static typing and [[id:63456626-b34e-46d9-b85e-0f1f5724aa83][lazy_evaluation]] . 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 [[https://www.haskell.org/downloads/][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:
  #+BEGIN_SRC haskell
  add :: Int -> Int -> Int
  add x y = x + y
  #+END_SRC
  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:
  #+BEGIN_SRC 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)
  #+END_SRC

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.