FunctorsRedux.fr

module learnyou.chapter11.FunctorsRedux where

import frege.data.Char ( toUpper )
import frege.data.List ( intersperse )

example1 :: IO ()
example1 = do
    line <- fmap (packed . reverse . unpacked) getLine
    putStrLn $ "You said " ++ line ++ " backwards!"
    putStrLn $ "Yes, you really said" ++ line ++ " backwards!"

example2 :: IO ()
example2 = do
    line <- fmap (packed . intersperse '-' . reverse . map toUpper . unpacked) getLine
    putStrLn line

data CMaybe a = CNothing | CJust Int a
derive Show (CMaybe a)

instance Functor CMaybe where
    fmap f CNothing          = CNothing
    fmap f (CJust counter x) = CJust (counter + 1) (f x)

main _ = do

    println $ fmap (* 3) (+ 100) 1
    println $ (* 3) `fmap` (+ 100) $ 1
    println $ (* 3) . (+ 100) $ 1
    println $ fmap (show . (* 3)) (* 100) 1

    println $ fmap (replicate 3) [ 1, 2, 3, 4 ]
    println $ fmap (replicate 3) (Just 4)
    println $ fmap (replicate 3) (Right "blah" :: (String | String))
    println $ fmap (replicate 3) (Nothing :: Maybe Int)
    println $ fmap (replicate 3) (Left "foo" :: (String | String))

    println $ fmap id (Just 3)
    println $ id (Just 3)
    println $ fmap id [ 1 .. 5 ]
    println $ id [ 1 .. 5 ]
    println $ fmap id ([] :: [Int])
    println $ fmap id (Nothing :: Maybe Int)

    println $ (CNothing :: CMaybe String)
    println $ CJust 0 "haha"
    println $ CJust 100 [ 1, 2, 3 ]

    println $ fmap (++ "ha") (CJust 0 "ho")
    println $ fmap (++ "he") (fmap (++ "ha") (CJust 0 "ho"))
    println $ fmap (++ "blah") CNothing

    println $ fmap id (CJust 0 "haha")
    println $ id (CJust 0 "haha")