# Installation The process for installing Haskell has changed. You now need to go here: [Downloads (haskell.org)](https://www.haskell.org/downloads/) # Using the Haskell Interpreter Once everything's installed, open the Haskell interpreter by either running ghci in a terminal or opening WinGHCi in Windows. The Haskell interpreter will load, showing the Prelude> prompt. Prelude refers to the standard module imported by default into all Haskell modules: it contains all the basic functions and types you need. Try out some arithmetic operators as follows: ```haskell Prelude> 3+4 7 Prelude> (5*6)+7 37 Prelude> 2^12 4096 ``` # Saving Your Work Haskell programs aren't intended to be written as line after line of code, but rather as a collection of functions. Haskell programs are a little like a spreadsheet: you write lots of functions that call each other. Here's an example of how to save your functions and load them into the interpreter. 1. Open your favourite text editor (Notepad, Notepad++, TextEdit, Emacs, Vim, …) and type in some Haskell functions. I've given two simple examples below. 2. ```haskell areaCircle x = 3.14 * x * x areaSquare x = x * x ``` 1. Save the file. I've saved my file as **c:/haskell/example.hs** 2. Run the Haskell interpreter 3. Type **:l c:/haskell/example.hs** to load your functions into the interpreter. You should see that the prompt now says Main>. Main refers to the module you just loaded. Note, you still have access to the Prelude functions 4. Experiment using your functions in the Haskell interpreter. If you make changes to your functions, hit **:r** to reload the file. ```haskell areaCircle 3 28.26 areaSquare 4 16 ``` # Exercise Write a functions to work out the following 1. The perimeter of circle 2. The perimeter of a square 3. The perimeter of a rectangle # Next - [[Lists]]