Chris McKinlay cmk

Reddit discussion.

Disclaimer 1: Type classes are great but they are not the right tool for every job. Enjoy some balance and balance to your balance.

Disclaimer 2: I should tidy this up but probably won’t.

Disclaimer 3: Yeah called it, better to be realistic.

Type classes are a language of their own, this is an attempt to document features and give a name to them.

deciban

The following table lists a number of rare events, arranged on a deciban scale. The deciban is a logarithmic unit — much like the decibel or the Richter scale — introduced by Alan Turing for expressing probabilities. It is a tenth of a ban, which is also known as the base-10 log-odds.

Please note that these are only rough estimates for the purpose of providing intuition for the relative likelihood of various rare events. Many are based on population averages, and do not apply to you personally. As always, keep the above comic in mind ;)

decibans	event

	#!/usr/bin/env stack
	-- stack --resolver lts-11.10 script
	import Control.Monad.Trans.Class
	import Control.Monad.IO.Class
	import Data.Functor.Identity

	newtype ReaderT r m a = ReaderT { runReaderT :: r -> m a }

	instance Functor m => Functor (ReaderT r m) where
	fmap f (ReaderT rma) = ReaderT $ fmap f . rma

	-- \| A 'Validator a b' is in particular a '(Applicative f, Choice p) => p a (f b)'.
	type Validator a b = a -> Validation ValidationErrors b

	-- \| Lift a 'Getting (Maybe a) s (Maybe a)' into a 'Prism'. This should only be used if the
	-- target domain type is a 'Maybe b'.
	--
	-- Note that error messages from 'Validator's consumed in this way are preserved.
	--
	-- @
	-- 'validating' :: Getting (Maybe a) s (Maybe a) -> Validator a b -> Validator s (Maybe b)

	{-# LANGUAGE FlexibleContexts #-}
	{-# LANGUAGE TupleSections #-}
	{-# LANGUAGE RankNTypes #-}

	import Data.Bifunctor
	import Data.Bifoldable
	import Data.Bifunctor.Join
	import Data.Biapplicative
	import Data.Bitraversable