YoEight

NotExist: Doesn't exist
NotPresent: Not submitted
NotNumber t@Text: "#{t}" is not a number
NotLetter t@Text: "#{t}" doesn't only contain letters
NotValidEmail t@Text: "#{t}" is not a valid email address
NotValidName t@Text: "#{t}" is not a valid name
ParsecError t@Text: Syntax error: #{t}
LengthGreater t@Text i@Int: "#{t}" is longer than #{show i} characters
LowerThan ii@Integer: is greater than #{show ii}
Invalid t@Text: #{show t} is invalid

YoEight

data Cofree f a = a :< (f (Cofree f a))

-- Fix point
newtype Mu f = Mu { unMu :: f (Mu f) }

extract :: Cofree f a -> a
extract (a :< _) = a

-- catamorphism
cata :: Functor f => (f b -> b) -> Mu f -> b

YoEight

{-# LANGUAGE GADTs, RankNTypes #-}

import Prelude hiding (read, print)

-- The "operational" form
data Action a where
    Print :: String -> Action ()
    Read :: Action String

{-

YoEight

{-# LANGUAGE GADTs #-}

data Free f a = Done a | Free (f (Free f a))

instance Functor f => Monad (Free f) where
    return = Done

    Done a >>= f = f a
    Free s >>= f = Free $ fmap (f =<<) s

YoEight

import Data.Functor.Foldable

-- | takeStrictlyLessThan take elements of a list whils their sum is
-- _strictly_ less than a given number
--
-- Point-free: I didnt' try without parameter, you can easily "hide" the 2nd
-- parameter (ie. takeStrictlyLessThan x = )
-- Level: MEDIUM
--
-- Examples:

YoEight

import Data.Traversable (for)

import Data.Aeson (Value, json)
import Data.AttoParsec (parseOnly)
import Snap.Core

getPostJsonParam :: MonadSnap m => ByteString -> m (Maybe Value)
getPostJsonParam key = do
    bsOpt <- getPostParam key
    for bsOpt $ \bs ->

YoEight

import Data.Functor.Foldable

divIfMultiple :: Integral a => a -> [a] -> Maybe [a]
divIfMultiple x = cata go
  where
    go Nil = Just []
    go (Cons a r)
        | mod a x == 0 = fmap (div a x:) r
        | otherwise    = Nothing

YoEight

{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE GADTs #-}
module Data.Process where

import Prelude hiding (zipWith)

import Control.Applicative
import Control.Monad
import Data.Foldable

YoEight

	Sun Feb  2 20:44 2014 Time and Allocation Profiling Report  (Final)

	   spellcheck +RTS -p -sstderr -RTS

	total time  =        0.00 secs   (0 ticks @ 1000 us, 1 processor)
	total alloc =      90,424 bytes  (excludes profiling overheads)

COST CENTRE MODULE           %time %alloc

CAF         GHC.IO.Handle.FD   0.0   38.4

YoEight

From d8730a5b72f263754e82c5e18ee53abf0c002b46 Mon Sep 17 00:00:00 2001
From: YoEight <yo.eight@gmail.com>
Date: Sat, 11 Jan 2014 13:30:23 +0100
Subject: [PATCH] Apply changes relative to TH.Pred becoming a TH.Type's
 synonym (issue #7021)

---
 compiler/deSugar/DsMeta.hs      | 53 +++++++++++++++++++----------------------
 compiler/hsSyn/Convert.lhs      | 16 +++++--------
 compiler/typecheck/TcSplice.lhs | 41 +++++++++++++++++++++++--------