cohama

maybeApply :: Maybe a -> (a -> Maybe b) -> Maybe b
maybeApply Nothing _ = Nothing
maybeApply (Just x) f = f x


Just 3 `applyMaybe` \x -> Just (x+1)

Just "smile" `applyMaybe` \x -> Just (x ++ " :) ")

Nothing `applyMaybe` \x -> Just (x+1)

cohama

class (Applicative m) => Monad m where
    return :: a -> m a

    (>>=) :: m a -> (a -> m b) -> m b

    (>>) :: m a -> m b -> m b
    x >> y = x >>= \_ -> y

    fail :: String -> m a
    fail msg = error msg

cohama

type Birds = Int
type Pole = (Birds, Birds)

-- 左に鳥が止まる
landLeft :: Birds -> Pole -> Pole
landLeft n (left, right) = (left + n, right)

-- 右に鳥が止まる
landRight :: Birds -> Pole -> Pole
landRight n (left, right) = (left, right + n)

cohama

type Birds = Int
type Pole = (Birds, Birds)

-- 左に鳥が止まる
landLeft :: Birds -> Pole -> Maybe Pole
landLeft n (left, right)
    | abs ((left + n) - right) < 4 = Just (left + n, right)
    | otherwise                    = Nothing

-- 右に鳥が止まる

cohama

import Data.Maybe

data Term = TmVar Int Int         {- deBruijn_index * term_length   -}
          | TmAbs String Term     {- bound_var_name * partial_term  -}
          | TmApp Term Term       {- arg_term       * applying_term -}
          | TmWrong String
          deriving (Eq)

data Binding = NameBind

cohama

こはまテイルズ会 #1

• 日時
  • 2014年5月5日(月)
• 集合
  • 13:00 に御器所駅2番出口付近集合
  • https://maps.google.co.jp/maps?q=35.149484,+136.935187&oe=utf-8&client=firefox-a&gbv=2&ie=UTF8&hl=ja&t=m&z=16&vpsrc=0&iwloc=A&brcurrent=3,0x60037082ac44e9ab:0x16c4d1ed824e6e55,0
• うちにあるゲーム

• TOS リマスター

cohama

TODOリスト

TODOリストのTODO

• TODOを追加できる

• ユーザはTODOの内容を入力する。
• 追加するためのコマンドを実行する。

• ✓最後に追加したTODOのみの詳細を見れる

• ユーザは最後に追加したTODOを取得できる
• 取得したTODOを表示できる

cohama

module RunProcessSimple where

import Control.Concurrent
import System.Exit
import System.IO
import System.Posix.IO
import System.Posix.Process
import System.Posix.Types
import Control.Exception

cohama

data Data = Data
    { dataID :: Int
    , dataName :: String
    , dataUrl :: String
    } deriving (Show)

-- save :: Data -> (Data -> IO ()) -> IO ()
-- save dat cont = do
--     print dat
--     cont (dat {dataID = 123, dataUrl = "/user/123"})

cohama

{-# LANGUAGE FlexibleInstances, FunctionalDependencies #-}
newtype MyState s a = MyState {runMyState :: s -> (a, s)}

instance Monad (MyState a) where
    return a = MyState $ \s -> (a, s)
    (MyState mys) >>= f = MyState $ \s -> let (a, s') = mys s in runMyState (f a) s'

class (Monad m) => MonadMyState s m | m -> s where
    put :: s -> m ()
    get :: m s