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4.3 KiB

Create a new Haskell Project

Writing a Haskell application can be quite challenging. You must know about:

  • setup your coding environment

    • get the right compiler

    • use libraries

    • handle your Haskell tooling, editor/IDE

  • project directory structure and best practices

    • write tests

    • benchmarks

    • profiling

  • Code architecture

    • encode the data structure

    • manage state and effects

This is both a manual and a tutorial. If you follow it, you should be familiar enough with Haskell to be able to write your own applications. I will focus on command line interfaces and REST APIs.

Haskell Environment Setup

My no brainer solution for it:

  1. Write this shell.nix file and launch nix-shell:

    { nixpkgs ? import (fetchGit {
      name = "nixos-release-19.09";
      url = "https://github.com/NixOS/nixpkgs";
      # obtained via
      # git ls-remote https://github.com/nixos/nixpkgs master
      ref = "refs/heads/nixpkgs-19.09-darwin";
      rev = "d5291756487d70bc336e33512a9baf9fa1788faf";
    }) { config = { allowBroken = true; }; } }:
    let
      inherit (nixpkgs) pkgs;
      inherit (pkgs) haskellPackages;
    
      haskellDeps = ps: with ps; [
        base
        protolude
        containers
      ];
    
      hspkgs = haskellPackages;
    
      ghc = hspkgs.ghcWithPackages haskellDeps;
    
      nixPackages = [
        ghc
        pkgs.gdb
        hspkgs.summoner
        hspkgs.summoner-tui
        haskellPackages.cabal-install
        haskellPackages.ghcid
      ];
    in
    pkgs.stdenv.mkDerivation {
      name = "env";
      buildInputs = nixPackages;
      shellHook = ''
            export PS1="\n\[[hs:\033[1;32m\]\W\[\033[0m\]]> "
         '';
    }
  2. now launch summon-tui

  3. add the following nix files: The first file to create is the one that will pin the versions of all your packages and libraries:

    import (fetchTarball https://github.com/NixOS/nixpkgs/archive/19.09.tar.gz) {}
    /yogsototh/her.esy.fun/src/commit/b6f4e8bf32a6c384c5b1961e93d3cd35c8473b4c/src/drafts/XXXX-Haskell-Projects/my-app/nixpkgs.nix

    The second file is the default.nix file:

    { nixpkgs ? import ./nixpkgs.nix
    , compiler ? "default"
    , doBenchmark ? false }:
    let
      inherit (nixpkgs) pkgs;
      name = "my-app";
      haskellPackages = pkgs.haskellPackages;
      variant = if doBenchmark
                then pkgs.haskell.lib.doBenchmark
                else pkgs.lib.id;
      drv = haskellPackages.callCabal2nix name ./. {};
    in
    {
      my_project = drv;
      shell = haskellPackages.shellFor {
        # generate hoogle doc
        withHoogle = true;
        packages = p: [drv];
        # packages dependencies (by default haskellPackages)
        buildInputs = with haskellPackages;
          [ hlint
            ghcid
            cabal-install
            cabal2nix
            hindent
            # # if you want to add some system lib like ncurses
            # # you could by writing it like:
            # pkgs.ncurses
          ];
        # nice prompt for the nix-shell
        shellHook = ''
         export PS1="\n\[[${name}:\033[1;32m\]\W\[\033[0m\]]> "
      '';
      };
    }
    /yogsototh/her.esy.fun/src/commit/b6f4e8bf32a6c384c5b1961e93d3cd35c8473b4c/src/drafts/XXXX-Haskell-Projects/my-app/default.nix

Retrieve Compiler

Dependency Management

Tooling

Haskell Project directoy structure

Tests

Benchmarks

Profiling

Haskell Code Architecture

Basic: IO

Easy: The Handle Pattern

Advanced: MTL

Expert: Free Monad