nickloewen

This is a plain-text version of Bret Victor’s reading list. It was requested by hf on Hacker News.

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Highly recommended things!

This is my five-star list. These are my favorite things in all the world.

A few of these works have had an extraordinary effect on my life or way of thinking. They get a sixth star. ★

andrejbauer

(* How do to topology in Coq if you are secretly an HOL fan.
   We will not use type classes or canonical structures because they
   count as "advanced" technology. But we will use notations.
 *)

(* We think of subsets as propositional functions.
   Thus, if [A] is a type [x : A] and [U] is a subset of [A],
   [U x] means "[x] is an element of [U]".
*)
Definition P (A : Type) := A -> Prop.

chrisdone

Typing Haskell in Haskell

MARK P. JONES

Pacific Software Research Center

Department of Computer Science and Engineering

Oregon Graduate Institute of Science and Technology

malisper

(defun multiple (a b)
  "Is A a multiple of B?"
  (= (mod a b) 0))

(defun next-fraction (n fractions)
  "Returns the next value of F in the Fractran program."
  (find-if (lambda (f)
             (integerp (* n f)))
           fractions))

regiskuckaertz

Derivations are the bread and butter of functional programming. It is easy to fall into the trap of thinking it is a pointless academic exercise, which is the reason why a lot of people struggle with FP. Functional programs are not so much written, they're calculated. It is here that the true power of equational reasoning (i.e. being able to swap the left and right parts of an equation everywhere in the code) help us.

So, getting comfortable reading and doing derivations is a must for any FP practitioner.

Below are the ones we did in the previous sessions, plus a couple of exercises.

Fold fusion

Blaisorblade

Fixpoint fib n :=
  match n with
  | 0 => 1
  | S n =>
    match n with
    | 0 => 1
    | S m => 
      fib n + fib m
    end
  end.

sjoerdvisscher

{-# LANGUAGE LinearTypes #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE BlockArguments #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE QualifiedDo #-}

import Prelude.Linear hiding (partition)
import qualified Control.Functor.Linear as Linear
import Control.Functor.Linear (State, state, execState, pure)
import qualified Data.Array.Mutable.Linear as Array

philzook58

(*|

I had a fun time giving a Z3 tutorial at Formal Methods for the Informal Engineer (FMIE) https://fmie2021.github.io/ (videos coming soon hopefully!). I got to be kind of the "fun dad" with the Z3 tutorial https://github.com/philzook58/z3_tutorial , while at times it felt a bit like Cody's Coq tutorial https://github.com/codyroux/broad-coq-tutorial was trying to feed the kids their vegetables. He knew it was going to be like this from the outset and had a fun little analogy of me downhill skiing while he was about to go on a cross country slog.

There are a number of factors to this. 
* I could use Z3's python bindings giving an air of familiarity, whereas everything was incredibly foreign in Coq.
* Z3 can actually be used to declaratively state problems and automatically calculate solutions to them with very little user help, which gives it a lot more "Wow" factor.
* Coq is a tool that requires significantly more background to even comprehend what the hell it is. I still think many aspects of it are tota

joepie91

The Freenode resignation FAQ, or: "what the fuck is going on?"

IMPORTANT NOTE:

It's come to my attention that some people have been spamming issue trackers with a link to this gist. While it's a good idea to inform people of the situation in principle, please do not do this. By all means spread the word in the communities that you are a part of, after verifying that they are not aware yet, but unsolicited spam is not helpful. It will just frustrate people.

Update 3 (May 24, 2021)

A number of things have happened since the last update.

siraben

Set Warnings "-notation-overridden,-parsing,-deprecated-hint-without-locality".
Require Import Arith.
Import Nat.
Require Import Lia.

(** * Reflexive transitive closure of a relation *)
Definition relation (X : Type) := X -> X -> Prop.
Inductive multi {X : Type} (R : relation X) : relation X :=
  | multi_refl : forall (x : X), multi R x x
  | multi_step : forall (x y z : X),