friedbrice

This now lives on GitHub: https://github.com/friedbrice/runhs

dcastro

import shapeless._, record._
import io.circe._
import io.circe.syntax._
import io.circe.generic.encoding._

case class Person(name: String, age: Int)

object Person {
  implicit val encodePerson: Encoder[Person] =
    ReprObjectEncoder.deriveReprObjectEncoder.contramap { person =>

domenkozar

1. Put ci.yaml into .github/workflows/
2. Follow https://github.com/cachix/cachix-action#usage to setup Cachix and benefit from quick CI build times.

jkachmar

{-# LANGUAGE ConstraintKinds            #-}
{-# LANGUAGE DataKinds                  #-}
{-# LANGUAGE FlexibleInstances          #-}
{-# LANGUAGE FunctionalDependencies     #-}
{-# LANGUAGE GADTs                      #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE InstanceSigs               #-}
{-# LANGUAGE LambdaCase                 #-}
{-# LANGUAGE NoImplicitPrelude          #-}
{-# LANGUAGE NoMonomorphismRestriction  #-}

pchiusano

This is material to go along with a 2014 Boston Haskell talk.

We are going to look at a series of type signatures in Haskell and explore how parametricity (or lack thereof) lets us constrain what a function is allowed to do.

Let's start with a decidedly non-generic function signature. What are the possible implementations of this function which typecheck?

wrangle :: Int -> Int

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

OliverJAsh

Option vs non-Option

	Option<T>	non-Option (T | undefined)
accessing property	userOption.map(user => user.age)	userNullish?.age
calling a method	userOption.map(user => user.fn())	userNullish?.fn()
providing fallback	ageOption.getOrElse(0)	ageNullish ?? 0
filter	ageOption.filter(checkIsOddNumber)	`ageNull

phette23

# put this in your .bash_profile
if [ $ITERM_SESSION_ID ]; then
  export PROMPT_COMMAND='echo -ne "\033];${PWD##*/}\007"; ':"$PROMPT_COMMAND";
fi

# Piece-by-Piece Explanation:
# the if condition makes sure we only screw with $PROMPT_COMMAND if we're in an iTerm environment
# iTerm happens to give each session a unique $ITERM_SESSION_ID we can use, $ITERM_PROFILE is an option too
# the $PROMPT_COMMAND environment variable is executed every time a command is run
# see: ss64.com/bash/syntax-prompt.html

edmundsmith

Method for Emulating Higher-Kinded Types in Rust

Intro

I've been fiddling about with an idea lately, looking at how higher-kinded types can be represented in such a way that we can reason with them in Rust here and now, without having to wait a couple years for what would be a significant change to the language and compiler.

There have been multiple discussions on introducing higher-ranked polymorphism into Rust, using Haskell-style Higher-Kinded Types (HKTs) or Scala-looking Generalised Associated Types (GATs). The benefit of higher-ranked polymorphism is to allow higher-level, richer abstractions and pattern expression than just the rank-1 polymorphism we have today.

As an example, currently we can express this type:

junegunn

# GIT heart FZF
# -------------

is_in_git_repo() {
  git rev-parse HEAD > /dev/null 2>&1
}

fzf-down() {
  fzf --height 50% --min-height 20 --border --bind ctrl-/:toggle-preview "$@"
}