1. Hello, Haskell!

In this step we’ll get a Haskell environment up and running.

Preparation

We can run Haskell programs in the browser without installing anything:

https://play.haskell.org/

To run Haskell on our computer, we have to install the GHC ¹ .

If you are on Linux, macOS, or Windows with WSL, then the recommended method of getting a development environment going is Nix with flakes:

• Install Nix
• Enable flakes
• Run nix shell nixpkgs#ghc

To proceed without Nix, follow the instructions here.

Verify that you have the GHC in your environment:

$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 9.0.2

GHCi: the Haskell playground

In either Replit or local installation of the GHC, we can enter an interactive environment with GHCi:

$ ghci
GHCi, version 9.0.2: https://www.haskell.org/ghc/  :? for help
ghci>

If using Nix, here is a quick one-liner:

$ nix shell nixpkgs#ghc --command ghci

Running our first program

Create the file hello.hs with the following contents:

main :: IO ()
main = putStrLn "Hello, Haskell!"

We can run the program directly with the following command:

$ runhaskell hello.hs
Hello, Haskell!

We can also compile the program to an executable, named the same as the source file:

$ ghc hello.hs
[1 of 1] Compiling Main             ( hello.hs, hello.o )
Linking hello ...

$ ./hello
Hello, Haskell!

On Linux and macOS, the executable will have no extension. On Windows it will have the extension .exe.