her.esy.fun/src/drafts/XXXX-Haskell-Projects/index.org

Create a new Haskell Project

• Haskell Environment Setup
  • 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

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/4ddc050e2c5b8cc8d8b03ad220228d224b66827c/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/4ddc050e2c5b8cc8d8b03ad220228d224b66827c/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