Hello World in Haskell

Welcome to the Hello World in Haskell page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

module Main where

main = putStrLn "Hello, World!"

Hello World in Haskell was written by:

• Jeremy Griffith

This article was written by:

• Jeremy Grifski
• rzuckerm

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

As usual, let's get right to our implementation of Hello World in Haskell.

First thing we will probably notice is that Haskell syntax is very different from Lisp and Scheme. Despite all three of those languages being functional, Haskell seems to have ditched the parentheses. In fact, even function calls lack parentheses in Haskell. That's a new one for me.

After the syntax, the next thing we should probably look at is that first line. As usual, we have a module declaration which basically declares this file as the main file. In other words, execution begins with this module. We saw something similar in our Hello World in Go article.

Finally, we have our main function. For someone who has never played with anything like Haskell, this syntax is a bit bizarre. In fact, the main function doesn't look like a function definition at all. At least, it doesn't look like what we've come to expect from this series.

That said, the main function does make a lot of sense if we think about it in terms of mathematics. After all, math functions follow the exact same form: f(x) = x.

At any rate, let's get back to the code. In this final line, we have the main keyword which indicates the entry point to the program. From there, we compute the expression on the other side of the equals sign. In this case, we have a print function (putStrLn) and our string, and that's it. Pretty simple!

How to Run the Solution

If we want to run the snippets above, we can use an online Haskell compiler. All we have to do is drop the code into the editor and hit run.

Of course, we can also run the code locally if we just grab a copy of the latest Glasgow Haskell Compiler. While we're downloading stuff, we should probably get a copy of the solution.

Assuming Haskell is now in the path, we can compile and run our solution using the following commands:

ghc hello-world.hs
hello-world.exe  # Windows
./hello-world  # Unix/Linux/Mac

And, that's it! The "Hello, World!" string should print straight to the console.