killercup

/*
 * I add this to html files generated with pandoc.
 */

html {
  font-size: 100%;
  overflow-y: scroll;
  -webkit-text-size-adjust: 100%;
  -ms-text-size-adjust: 100%;
}

gelisam

-- in reply to http://www.reddit.com/r/haskell/comments/21mja6/make_lllegal_state_transitions_unrepresentable/
-- 
-- We implement a tiny language with three commands: Open, Close, and Get.
-- The first Get after an Open returns 1, the second Get returns 2, and so on.
-- 
-- Get is only valid while the state is open, and
-- Open must always be matched by a Close.
-- We enforce both restrictions via the type system.
-- 
-- There are two valid states: Opened and Closed.

ocharles

{-# LANGUAGE GeneralizedNewtypeDeriving #-}

import Control.Monad.IO.Class
import Control.Monad.Trans.Class
import Prelude hiding (log)

--------------------------------------------------------------------------------
-- The API for cloud files.
class Monad m => MonadCloud m where
  saveFile :: Path -> Bytes -> m ()

CMCDragonkai

Existential Types in Haskell

I had always been confused by Haskell's implementation of existential types. Until now!

Existential types is the algebraic data type (ADT) equivalent to OOP's data encapsulation. It's a way of hiding a type within a type. Hiding it in such a way that any consumer of the data type won't have any knowledge on the internal property

Icelandjack

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.

yossorion

What I Wish I'd Known About Equity Before Joining A Unicorn

Disclaimer: This piece is written anonymously. The names of a few particular companies are mentioned, but as common examples only.

This is a short write-up on things that I wish I'd known and considered before joining a private company (aka startup, aka unicorn in some cases). I'm not trying to make the case that you should never join a private company, but the power imbalance between founder and employee is extreme, and that potential candidates would

chrisdone

labels vs vinyl vs record vs lens

Advantages and disadvantages of each are explored here.

vinyl

Pros

• Support arbitrary number of fields
• Supports projecting and narrow and things like that quite well

chrisdone

{-# LANGUAGE TemplateHaskell #-}
-- | For when you have a record that doesn't have lenses derived for
-- it and you need a lens, just use @$(lens 'thefield)@ and away you go.
module Control.Lens.FieldTH where
import Language.Haskell.TH
lens :: Name -> Q Exp
lens name = do
  [|\f r ->
      fmap
        $(lamE

mtesseract

The Problem

Defining records in Haskell causes accessor functions for the record's fields to be defined. There is no seperate namespace for these accessor functions.

The Goal

Be able to

• use records in Haskell, which share field names.
• use lenses for accessing these fields

mrkgnao

{-# LANGUAGE ApplicativeDo           #-}
{-# LANGUAGE ConstrainedClassMethods #-}
{-# LANGUAGE ConstraintKinds         #-}
{-# LANGUAGE DataKinds               #-}
{-# LANGUAGE DeriveFunctor           #-}
{-# LANGUAGE DeriveGeneric           #-}
{-# LANGUAGE FlexibleContexts        #-}
{-# LANGUAGE FlexibleInstances       #-}
{-# LANGUAGE IncoherentInstances     #-}
{-# LANGUAGE InstanceSigs            #-}