PLT-14 IO Monad

Transcript

1. pineapple.cc ۚ୩Ұ࿕ʢ௕࡚େֶ৘ใσʔλՊֶ෦ʣ *0Ϟφυ ϓϩάϥϛϯάݴޠ࿦
2. pineapple.cc fx ≡ { ⟨1/x⟩ if x ≠ 0 ∅ otherwise
3. pineapple.cc fx ≡ { ⟨1/x⟩ if x ≠ 0 ∅ otherwise gx ≡ 2.0 × x
4. pineapple.cc fx ≡ { ⟨1/x⟩ if x ≠ 0 ∅ otherwise gx ≡ 2.0 × x g′  x ≡ ⟨gx⟩
5. pineapple.cc fx ≡ { ⟨1/x⟩ if x ≠ 0 ∅ otherwise gx ≡ 2.0 × x g′  x ≡ ⟨gx⟩ x′  ≡ (g′  ∘ f)x
6. pineapple.cc fx ≡ { ⟨1/x⟩ if x ≠ 0 ∅ otherwise gx ≡ 2.0 × x g′  x ≡ ⟨gx⟩ x′  ≡ ⟨x⟩ ↣ f ↣ g′ 
7. pineapple.cc f :: Float -> Maybe Float f x = if x /= 0 then Just (1/x) else Nothing g :: Float -> Float g x = 2.0*x g’ :: Float -> Maybe Float g’ x = Just (g x) x’ = Just 2 >>= f >>= g’
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15. pineapple.cc x :: String x = “Hello, world!” main = print x
16. pineapple.cc x :: IO String x = getLine main = x >>= print
17. pineapple.cc x :: IO String x = getLine f :: String -> String f x = if length x > 3 then “Too long.” else x main = (f x) >>= print
18. pineapple.cc x :: IO String x = getLine f :: String -> IO String f x = if length x > 3 then return “Too long.” else return x main = (f x) >>= print
19. pineapple.cc x :: IO String x = getLine f :: IO String -> IO String f x = x >>= (\x’ -> if length x’ > 3 then return “Too long.” else return x’) main = (f x) >>= print
20. pineapple.cc x :: IO String x = getLine f :: String -> String f x = if length x > 3 then “Too long.” else x f’ :: IO String -> IO String f’ = liftM f main = (f' x) >>= print ผղ
21. pineapple.cc x :: IO String x = getLine f :: String -> String f x = if length x > 3 then “Too long.” else x f’ :: IO String -> IO String f’ = liftM f main = (return x) >>= f’ >>= print ผղ
22. pineapple.cc x :: IO String x = getLine f :: String -> String f x = if length x > 3 then “Too long.” else x main = x >>= (\x’ -> return (f x’)) >>= print ผղ