Main.hs

-- Deep Learning from Scratch
-- Chapter 01
module Ch01.Main where

import Prelude hiding (lookup)
import Control.Monad

main :: IO ()
main = do
    -- 算術計算
    let a1 = 1 - 2
    let a2 = 4 * 5
    let a3 = 7 / 5
    let a4 = 3 ^ 2

    putStrLn $ show a1
    putStrLn $ show a2
    putStrLn $ show a3
    putStrLn $ show a4

    -- データ型
    -- Prelude> :t 10
    -- 10 :: Num t => t
    -- Prelude> :t 2.718
    -- 2.718 :: Fractional t => t
    -- Prelude> :t "hello"
    -- "hello" :: [Char]

    -- 変数
    let x = 10
    putStrLn $ show x
    let x = 100  -- Fractal型
    putStrLn $ show x
    let y = 3.14
    putStrLn $ show (x * y)

    -- 配列(リスト)
    let a = [1,2,3,4,5]

    putStrLn $ show a
    putStrLn $ show $ length a
    putStrLn $ show $ a !! 0
    putStrLn $ show $ a !! 4

    let a' = insert 4 99 a
    putStrLn $ show $ a'

    putStrLn $ show $ take 2 a'
    putStrLn $ show $ drop 1 a'
    putStrLn $ show $ take 3 a'
    putStrLn $ show $ take (length a' - 1) a'

    -- ディクショナリ
    let me  = [("height", 180)]
    let me' = ("weight", 70):me
    putStrLn $ show $ me
    putStrLn $ show $ me'

    -- ブーリアン
    let hungry = True
    let sleepy = False
    putStrLn $ show $ not hungry
    putStrLn $ show $ hungry && sleepy
    putStrLn $ show $ hungry || sleepy

    -- if
    when hungry $ putStrLn "I'm hungry"
    let hungry = False
    if hungry then putStrLn "I'm hungry"
              else putStrLn "I'm not hungry" >>
                   putStrLn "I'm sleepy"

    -- for
    -- [IO ()]
    for (\i -> putStrLn $ show i) [1,2,3]

-- 補助関数

-- 配列(リスト)
insert :: Int -> Int -> [Int] -> [Int]
insert i v lst =
    let idx = (length lst) - i in
    foldr (\x acc -> if length (x:acc) == idx then v:acc else x:acc) [] lst

-- ディクショナリ
lookup :: (Eq k) => k -> [(k,v)] -> Maybe v
lookup key []   = Nothing
lookup key ((k,v):rest)
    | key == k  = Just v
    | otherwise = lookup key rest

-- Pythonのディクショナリ
-- >>> me = {'height':180}
-- >>> me['height']
-- 180
-- >>> me['weight'] = 70
-- >>> me
-- {'weight': 70, 'height': 180}

-- >> me['hoge']
-- Traceback (most recent call last):
--   File "<stdin>", line 1, in <module>
-- KeyError: 'hoge'

-- for
for f = map f