shigemk2

import Data.Monoid

main = do
    print $ LT `mappend` GT
    print $ GT `mappend` LT
    print $ mempty `mappend` LT
    print $ mempty `mappend` GT

shigemk2

import Data.Monoid

-- newtypeにくるむ
-- この方法は面倒なので、orとかandとか使ったほうがいい
main = do
    print $ getAny $ Any True `mappend` Any False
    print $ getAny $ mempty `mappend` Any True
    print $ getAny . mconcat . map Any $ [False, False, False, True]
    print $ getAny $ mempty `mappend` mempty

shigemk2

import Data.Monoid

-- getProductなどでモノイドの中身の値を取り出す
main = do
    -- product
    print $ Product 3 `mappend` Product 9
    print $ getProduct $ Product 3 `mappend` Product 9
    print $ getProduct $ Product 3 `mappend` mempty
    print $ getProduct $ Product 3 `mappend` Product 4 `mappend` Product 2
    print $ getProduct $ Product 3 `mappend` (Product 4 `mappend` Product 2)

shigemk2

import Data.Monoid

-- instance Monoid [a] where
--     mempty = []
--     mappend = (++)

main = do
    print $ [1,2,3] `mappend` [4,5,6]
    print $ ("one" `mappend` "two") `mappend` "tree"
    print $ "one" `mappend` ("two" `mappend` "tree")

shigemk2

import Data.Monoid

-- instance Monoid [a] where
--     mempty = []
--     mappend = (++)

main = do
    print $ [1,2,3] `mappend` [4,5,6]
    print $ ("one" `mappend` "two") `mappend` "tree"
    print $ "one" `mappend` ("two" `mappend` "tree")

shigemk2

main = do
    print $ (3 * 2) * (8 * 5)
    print $ 3 * (2 * (8 * 5))
    print $ "la" ++ ("di" ++ "ga")
    print $ ("la" ++ "di") ++ "ga"

shigemk2

-- data CoolBool = CoolBool { getCoolBool :: Bool }
newtype CoolBool = CoolBool { getCoolBool :: Bool }

helloMe :: CoolBool -> String
helloMe (CoolBool _ ) = "hello"


main = do
    print $ helloMe undefined

shigemk2

import Control.Applicative

sequenceA :: (Applicative f) => [f a] -> f [a]
sequenceA = foldr (liftA2 (:)) (pure [])

main = do
    print $ sequenceA [Just 1, Just 2]
    print $ sequenceA [Just 3, Just 2, Just 1]
    print $ sequenceA [Just 3, Nothing, Just 1]
    print $ sequenceA [[1,2,3],[4,5,6]]

shigemk2

import scala.language.implicitConversions

// R is derived from Rational with some fixes.
// https://sites.google.com/site/scalajp/home/documentation/scala-by-example/chapter6

case class R(numer: Int, denom: Int) extends Ordered[R] {
  def reduce: R = {
    def gcd(x: Int, y: Int): Int = {
      if (x == 0) y
      else if (x < 0)  gcd(-x,  y)

shigemk2

import scalaz._
import Scalaz._

object Gcd {
  def main(args: Array[String]): Unit = {
    def gcd(a: Int, b: Int): Writer[List[String], Int] =
      if (b == 0) for {
        _ <- List("Finished with " + a.shows).tell
      } yield a
      else