friedbrice

-- ghcid -c'stack repl --resolver nightly --package time' haskell-time.hs --allow-eval

----
-- # Haskell Time Crib Sheet
----

-- Excellent sources for this small guide include:
--
--   * https://two-wrongs.com/haskell-time-library-tutorial.html
--   * https://williamyaoh.com/posts/2019-09-16-time-cheatsheet.html

ObjectBoxPC

import Data.Char (toUpper)
import Data.List (intercalate)
import Data.List.NonEmpty (NonEmpty, nonEmpty, toList)
import System.Environment (getArgs)

data PangramResult = Pangram | MissingLetters (NonEmpty Char)

checkPangram :: String -> PangramResult
checkPangram s = case nonEmpty missingLetters of
    Just ls -> MissingLetters ls

friedbrice

-- monadstate-example.hs
--
-- Load this program in GHCi:
--
--     stack repl \
--         --resolver nightly \
--         --package transformers \
--         --package mtl \
--         monadstate-example.hs
--

gelisam

-- in response to https://twitter.com/chrislpenner/status/1221784005156036608
--
-- The goal is to mimic this Scala code, but in Haskell:
--
-- > "spotify:user:123:playlist:456" match {
-- >   case s"spotify:user:$userId:playlist:$playlistId"
-- >     => ($userId, $playlistId)  // ("123", "456")
-- > }
{-# LANGUAGE DeriveFunctor, LambdaCase, PatternSynonyms, QuasiQuotes, RankNTypes, TemplateHaskell, TypeOperators, ViewPatterns #-}
{-# OPTIONS -Wno-name-shadowing #-}

piq9117

{-# LANGUAGE EmptyDataDecls             #-}
{-# LANGUAGE FlexibleContexts           #-}
{-# LANGUAGE GADTs                      #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses      #-}
{-# LANGUAGE OverloadedStrings          #-}
{-# LANGUAGE QuasiQuotes                #-}
{-# LANGUAGE TemplateHaskell            #-}
{-# LANGUAGE TypeFamilies               #-}

chrisdone

Statically checked overloaded strings

This gist demonstrates a trick I came up with which is defining IsString for Q (TExp a), where a is lift-able. This allows you to write $$("...") and have the string parsed at compile-time.

On GHC 9, you are able to write $$"..." instead.

This offers a light-weight way to enforce compile-time constraints. It's basically OverloadedStrings with static checks. The inferred return type

nrinaudo

Introduction

I was recently asked to explain why I felt disappointed by Haskell, as a language. And, well. Crucified for crucified, I might as well criticise Haskell publicly.

First though, I need to make it explicit that I claim no particular skill with the language - I will in fact vehemently (and convincingly!) argue that I'm a terrible Haskell programmer. And what I'm about to explain is not meant as The Truth, but my current understanding, potentially flawed, incomplete, or flat out incorrect. I welcome any attempt at proving me wrong, because when I dislike something that so many clever people worship, it's usually because I missed an important detail.

Another important point is that this is not meant to convey the idea that Haskell is a bad language. I do feel, however, that the vocal, and sometimes aggressive, reverence in which it's held might lead people to have unreasonable expectations. It certainly was my case, and the reason I'm writing this.

Type classes

I love the concept of type class

fiddlerwoaroof

//
// Two kinds of animals: dogs and cats
//
// I want greet and leave to be defined such that there are four
// different behaviors corresponding to each combination of dog and
// cat
//
class Animal {
  receive_operation(operation) {
    console.log("the animal is unresponsive");

friedbrice

var danielsLensTalk = {
    recordId: 0,
    creation: {
        user: 'danielbrice@gmail.com',
        moment: {
            date: {
                year: 2019,
                month: 5,
                day: 29
            },

eborden

project=$(basename "$(pwd)")

# build dependencies
build_deps="stack build $project --fast --pedantic --dependencies-only --interleaved-output"

# restart on changes in other packages
restarts=$(find ../. -maxdepth 1 -type d \
  -not -name "$project" \
  -not -name .stack-work \
  -not -name . \