tonyday567

In this gist we will first show that we can beat the arc challenge
(http://www.paulgraham.com/arcchallenge.html), and then build the library that
shows how we did it. This gist is Literate Haskell and is of course executable. The packages needed are happstack-server and applicative-extras, installable using cabal.

Let's start with some imports (for now, you can ignore these)

> {-# LANGUAGE GADTs, TypeSynonymInstances #-}
> module ArcChallenge where
>
> import Control.Applicative

tonyday567

body {
  font-family: Helvetica, arial, sans-serif;
  font-size: 14px;
  line-height: 1.6;
  padding-top: 10px;
  padding-bottom: 10px;
  background-color: white;
  padding: 30px; }

body > *:first-child {

tonyday567

{-# language DataKinds, PolyKinds, ScopedTypeVariables, UndecidableInstances,
    FlexibleInstances, FlexibleContexts, GADTs, TypeFamilies, RankNTypes,
    LambdaCase, TypeOperators, ConstraintKinds #-}

import GHC.TypeLits
import Data.Proxy
import Data.Singletons.Prelude
import Data.Singletons.Decide
import Data.Constraint