Haskell/Getting set up

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This chapter describes how to install the programs you'll need to start coding in Haskell.

Installing Haskell[edit]

Haskell is a programming language, i.e. a language in which humans can express how computers should behave. It's like writing a cooking recipe: you write the recipe and the computer executes it.

To use Haskell programs, you need a special program called a Haskell compiler. A compiler takes code written in Haskell and translates it into machine code, a more primitive language that the computer understands. Using the cooking analogy, you write a recipe (your Haskell program) and a cook (a compiler program) does the work of putting together actual ingredients into an edible dish (an executable file). Of course, you can't easily get the recipe from a final dish (and you can't get the Haskell program code from executable after it's compiled).

To start learning Haskell, download and install the Haskell platform. It will contain the "Glasgow Haskell Compiler", or GHC, and everything else you need.

If you're just trying out Haskell, or are averse to downloading and installing the full compiler, you can try Hugs, the lightweight Haskell interpreter (it also happens to be portable). You might also like to play around with TryHaskell, an interpreter hosted online. Note that all instructions here will be for GHC.


UNIX users:

If you are a person who prefers to compile from source: This might be a bad idea with GHC, especially if it's the first time you install it. GHC is itself mostly written in Haskell, so trying to bootstrap it by hand from source is very tricky. Besides, the build takes a very long time and consumes a lot of disk space. If you are sure that you want to build GHC from the source, see Building and Porting GHC at the GHC homepage.

In short, we strongly recommend downloading the Haskell Platform instead of compiling from source.

Very first steps[edit]

After you have installed the Haskell Platform, it's now time to write your first Haskell code.

For that, you will use the program called GHCi (the 'i' stands for 'interactive'). Depending on your operating system, perform the following steps:

  • On Windows: Click Start, then Run, then type 'cmd' and hit Enter, then type ghci and hit Enter once more.
  • On MacOS: Open the application "Terminal" found in the "Applications/Utilities" folder, type the letters ghci into the window that appears and hit the Enter key.
  • On Linux: Open a terminal and run the ghci program.

You should get output that looks something like the following:

GHCi, version 7.6.3: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.

The first bit is GHCi's version. It then informs you it's loading the base package, so you'll have access to most of the built-in functions and modules that come with GHC. Finally, the Prelude> bit is known as the prompt. This is where you enter commands, and GHCi will respond with their results.

Now you're ready to write your first Haskell code. In particular, let's try some basic arithmetic:

Prelude> 2 + 2
Prelude> 5 + 4 * 3
Prelude> 2 ^ 5

The operators are similar to what they are in other languages: + is addition, * is multiplication, and ^ is exponentiation (raising to the power of, or a ^ b). Note from the second example that Haskell follows standard order of operations.

Now you know how to use Haskell as a calculator. Actually, Haskell is always basically a calculator - a really powerful one, able to deal not only with numbers but also with other objects like characters, lists, functions, trees, and even other programs (if you aren't familiar with these terms yet, don't worry).

GHCi is a very powerful development environment. As we progress, we will learn how we can load files with source code into GHCi, and evaluate different parts of them.

If you're clear on everything so far (if not, use the talk page and help us improve this Wikibook!), then you are ready for next chapter, in which we will introduce some of the basic concepts of Haskell, along with our first Haskell functions.