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Haskell Tutorial: Validity, GenValid, Recursion Schemes, and Testing with Tasty

This tutorial demonstrates using the validity and genvalidity packages along with recursion schemes and both property-based and unit testing using tasty-quickcheck and tasty-hunit for a simple arithmetic expression evaluator.

Setup

First, let's update our project structure:

validity-tutorial/

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module Telomare.Cesar where

import Data.Char (ord, chr, isLetter, isLower)
import Text.Read (Lexeme(Char))

input = unlines $ [ "11"
                  , "middle-Outz"
                  , "2"
                  ]

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╭─hhefesto@olimpo ~/src/telomare ‹master●› 
╰─$ haskell-language-server --debug src/Telomare.hs                                                                                                            ghc-shell-for-telomare-0.1.0.0
2022-05-23T15:03:34.362602Z | Info | No log file specified; using stderr.
2022-05-23T15:03:34.362939Z | Info | haskell-language-server version: 1.7.0.0 (GHC: 9.2.2) (PATH: /nix/store/6svi1lnknjygjl6qsfckxvv4iizi0rn0-haskell-language-server-1.7.0.0/bin/haskell-language-server)
2022-05-23T15:03:34.363348Z | Info | Directory: /home/hhefesto/src/telomare
2022-05-23T15:03:34.363506Z | Info | Logging heap statistics every 60.00s
 ghcide setup tester in /home/hhefesto/src/telomare.
Report bugs at https://github.com/haskell/haskell-language-server/issues

Step 1/4: Finding files to test in /home/hhefesto/src/telomare

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# Edit this configuration file to define what should be installed on
# your system.  Help is available in the configuration.nix(5) man page
# and in the NixOS manual (accessible by running ‘nixos-help’).

{ config, pkgs, ... }:

{
  imports =
    [ # Include the results of the hardware scan.
      ./hardware-configuration.nix

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diff --git a/Prelude.tel b/Prelude.tel
index 555aa9f..8908c75 100644
--- a/Prelude.tel
+++ b/Prelude.tel
@@ -89,3 +89,6 @@ quicksort = let layer = \recur l -> if right l
                                             in listPlus (recur p2) (t,(recur p1))
                                        else l
             in ? layer (\l -> 0)
+
+abort = \str -> let x : (\y -> listPlus "abort: " str) = 1

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{
  "nodes": {
    "fenix": {
      "inputs": {
        "nixpkgs": [
          "solanaNix",
          "nixpkgs"
        ],
        "rust-analyzer-src": "rust-analyzer-src"
      },

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let
  gcOverlay = self: super: {
    # jumper = telomare_jumper;
    gc = self.boehmgc;
  };
in

{ # Fetch the latest haskell.nix and import its default.nix
  # haskellNix ? import (builtins.fetchTarball "https://github.com/input-output-hk/haskell.nix/archive/dc7acfeb7628032d5109747a8b330d58817b953f.tar.gz") {}
  haskellNix ? import (builtins.fetchTarball "https://github.com/input-output-hk/haskell.nix/archive/master.tar.gz") { overlays = [ gcOverlay ]; }

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;;; $DOOMDIR/config.el -*- lexical-binding: t; -*-

;; Place your private configuration here! Remember, you do not need to run 'doom
;; sync' after modifying this file!


;; Some functionality uses this to identify you, e.g. GPG configuration, email
;; clients, file templates and snippets.
(setq user-full-name "Daniel Herrera Rendón")
(setq user-mail-address "[email protected]")

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{ rev1 ? "78d05675a4186c3b7b2de214f3c3b245ba0d2fa5",
  # rev ? "1a92d0abfcdbafc5c6e2fdc24abf2cc5e011ad5a",
  outputSha256 ? "0aam50m1w1kqfdhwnazzi6jdq422d3ib3ilvb1m5lcr5jn7nhf1f",
  # enableLLVMAssertions ? true
  enableLLVMAssertions ? false
}:

with rec {
  nixpkgs = (import <nixpkgs> { }).fetchFromGitHub {
    # a = true;

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{
  laurus = {pkgs, ...}:{
    networking.firewall.allowedTCPPorts = [ 22 80 5432 587 443 ];

    nixpkgs.config = import ~/src/laurus-nobilis/config.nix;

    systemd.services.laurus-nobilis =
      { description = "laurus-nobilis";
        enable = true;
        wantedBy = [ "multi-user.target" "nginx.service" ];