Getting started

First-time setup

If this is your first time using Nix or haskell-template (or a project based on it) you will initially need to setup a few things on your system.


  • Install Nix (version must be 2.8 or greater)
    • If you are using Windows, you may install Nix under WSL2
  • Enable Flakes
  • In the project directory, run nix develop -i -c haskell-language-server to sanity check your environment.
    • This will download the required dependencies and cache them to the local Nix store. If it succeeds, it means everything’s good.


While you may use any text editor with language-server support, we will use VSCode because it is generally the easiest way to get started.

  • Launch VSCode, and open the git clone’ed project directory as single-folder workspace
  • When prompted by VSCode, install the workspace recommended extensions.
    • If it doesn’t prompt, press Ctrl+Shift+X and search for @recommended to install them all manually.
  • Press Ctrl+Shift+P to run the command “Nix-Env: Select Environment” and then select shell.nix.
    • The extension will ask you to reload VSCode at the end. Do it.
    • Note: We recommend that you switch to using direnv; see here for details.

Running in VSCode

Once the project has been reloaded in VSCode, you are ready to start developing it. But first, it is useful to sanity check a few things:

Test that haskell-language-server works

  • Open src/Main.hs.
    • Notice haskell-language-server launching in the footer (you should see “Processing (1/2)”), and wait for it finish.
  • Hover your mouse over something, say putTextLn, and see the hover tooltip giving you the type signature.
    • This means the IDE support works!

Test that ghcid works

  • Launch the terminal inside VSCode
  • Run nix develop shell and run just run.
    • This will launch ghcid to run the main entrypoint in src/Main.hs.
  • Modify src/Main.hs and save it.

This should have just run instantly re-compile and re-run the program.

Note: you can also press Ctrl+Shift+B to run just run.

Rename the project

Finally, if you are going to be using this template for a real project, you should rename it.

# First, click the green "Use this template" button on GitHub to create your copy
# You may name the new repository to be the same as $NAME
git clone <your-clone-url> $NAME
cd $NAME

# Copy-paste these 4 lines at the same time
git mv haskell-template.cabal ${NAME}.cabal
nix run nixpkgs\#sd -- haskell-template ${NAME} * */*
echo "# ${NAME}\n\n" >
git add . && git commit -m rename

Next steps

See haskell-template for further documentation.

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