kbridge

Understanding the Phases Applicative

While I was researching how to do level-order traversals of a binary tree in Haskell, I came across a library called tree-traversals which introduced a fancy Applicative instance called Phases. It took me a lot of effort to understand how it works. Although I still have some unresolved issues, I want to share my journey.

Note: I was planning to post this article on Reddit. But I gave up because it was too long so here might be a better place.

See the discussion.

Note: This article is written in a beginner-friendly way. Experts may find it tedious.

quad

Interceptors Are Functions Too

I could not agree more with my colleague and friend Travis Johnson's opinion that "[INTERCEPTORS ARE SO COOL][iasc]!" In that post, he succinctly describes the [Interceptor pattern][pattern] as used adroitly by [OkHttp][okhttp]. But, as is often the case, I believe a complicated object-oriented pattern obscures the simple functional gem within it.

What is an Interceptor?

I'll quote liberally from [OkHttp's documentation on the topic][okhttp-interceptor]:

Interceptors are a powerful mechanism that can monitor, rewrite, and retry calls. […] >

zanzix

infixr 5 ~~> -- Morphisms of graphs

-- | Boilerplate for recursion schemes

-- Objects are graphs 
Graph : Type -> Type 
Graph o = o -> o -> Type 

-- Morphisms are vertex-preserving transformations between graphs

zanzix

infixr 5 +++
infixr 5 ***

-- A list over a type
-- data List : Type -> Type where 
--   Nil : List a 
--   (::) : a -> List a -> List a 

Graph : Type -> Type 
Graph obj = obj -> obj -> Type 

cpursley

PostgreSQL is Enough

• Simplify: move code into database functions
• Just Use Postgres for Everything
• PostgreSQL is the worlds’ best database
• Postgres is eating the database world
• Hacker News discussion

Background and Cron Jobs

kconner

macOS Internals

Understand your Mac and iPhone more deeply by tracing the evolution of Mac OS X from prelease to Swift. John Siracusa delivers the details.

Starting Points

How to use this gist

You've got two main options:

VladimirReshetnikov

https://chat.openai.com/chat?model=gpt-4

User:

Propose a meaningful implementation of a Haskell function of type f :: (a → (Maybe a, b)) → a → [b]

---

ChatGPT:

peterstorm

{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE InstanceSigs #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE StandaloneKindSignatures #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies #-}

Lysxia

{-# LANGUAGE
  DataKinds,
  DeriveGeneric,
  PolyKinds,
  StandaloneDeriving,
  TypeFamilies,
  UndecidableInstances #-}
module T where

import Data.Kind (Constraint, Type)

chrisdone-artificial

{-

Examples:

> reify @Int $ eval $ A (reflect (abs :: Int -> Int)) (I (-9))
9

> reify @Int $ eval $ A (A (reflect ((*) :: Int -> Int -> Int)) (reflect @Int 3)) (reflect @Int 5)
15