Maintainable Software Architecture in Haskell

This talk is perfect for Developers who are interested in seeing Haskell being used as a general programming language. Engineers who are hoping to see Haskell as an environment in which they can quickly and effectively iterate between requirements, design and running executable code: providing value to the business with an immediate feedback loop.

Transcript

1. Maintainable So,ware Architeture in Haskell (with Polysemy) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 1
2. maintain [ meyn-teyn ] verb (used with object) 1. to keep in existence 2. to keep in an appropriate condi2on, opera2on, or force; keep unimpaired: 3. to keep in a specified state, posi2on, etc. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 2
3. maintain [ meyn-teyn ] verb (used with object) 1. to keep in existence 2. to keep in an appropriate condi.on, opera/on, or force; keep unimpaired: 3. to keep in a specified state, posi/on, etc. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 3
4. maintain [ meyn-teyn ] verb (used with object) 1. to keep in existence 2. to keep in an appropriate condi.on, opera/on, or force; keep unimpaired: 3. to keep in a specified state, posi/on, etc. ... in Haskell? © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 4
5. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 5
6. "Socialism Haskell is a system language which heroically overcomes difficul9es unknown in any other system language" © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 6
7. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 7
8. Emphasis on what, less focus on why? © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 8
9. Maintainable So,ware Architeture in Haskell © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 9
10. Our plan for today 1. Coding Dojo / Hack day 2. Real world example • problem • approach • consequences • Polysemy © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 10
11. Does wri)ng code sucks? © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 11
12. Why wri(ng code sucks (some(mes)? © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 12
13. Coding Kata: Write a sor0ng algorithm © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 13
14. "As a Billing System user I want to generate an invoice for a given account based on its current system use" © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 14
15. Func%ons and their nature 1. Manipulate data (f :: Input -> Output) 2. Interact with an outside world © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 15
16. doStuff :: Int -> Int doStuff i = i + 1 Why this func,on is soooo good? • easy to test • you will be no/fied if its behavior changes © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 16
17. It's easy to maintain func0on if it only manipulates data. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 17
18. -- | take an Int (i) and UUID (uuid) as parameters -- | fetch existing Int under given uuid from MongoDB -- | (if does not exist, default to zero) -- | add them, store the result, return result as text doStuff :: UUID -> Int -> IO String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 18
19. -- | take an Int (i) and UUID (uuid) as parameters -- | fetch existing Int under given uuid from MongoDB -- | (if does not exist, default to zero) -- | add them, store the result, return result as text doStuff :: UUID -> Int -> IO String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 19
20. -- | take an Int (i) and UUID (uuid) as parameters -- | fetch existing Int under given uuid from MongoDB -- | (if does not exist, default to zero) -- | add them, store the result, return result as text doStuff :: UUID -> Int -> IO String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 20
21. -- | take an Int (i) and UUID (uuid) as parameters -- | fetch existing Int under given uuid from MongoDB -- | (if does not exist, default to zero) -- | add them, store the result, return result as text doStuff :: UUID -> Int -> IO String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 21
22. -- | take an Int (i) and UUID (uuid) as parameters -- | fetch existing Int under given uuid from MongoDB -- | (if does not exist, default to zero) -- | add them, store the result, return result as text doStuff :: UUID -> Int -> IO String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 22
23. -- | take an Int (i) and UUID (uuid) as parameters -- | fetch existing Int under given uuid from MongoDB -- | (if does not exist, default to zero) -- | add them, store the result, return result as text doStuff :: UUID -> Int -> IO String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 23
24. It's easy to test and maintain func1on if it only manipulates data. Can we change "interac.ons with the outside world" into data? © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 24
25. -- | take an Int (i) and UUID (uuid) as parameters -- | fetch existing Int under given uuid from MongoDB -- | (if does not exist, default to zero) -- | add them, store the result, return result as text doStuff :: UUID -> Int -> IO String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 25
26. Let's start with something simple © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 26
27. -- | take Int, return +1 as text doStuff :: Int -> String doStuff i = "New value: " ++ (show $ i + 1) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 27
28. prop_returns_plus1 :: Property prop_returns_plus1 = property do -- given i <- Gen.int -- when let res = doStuff i -- then res === "New value: " ++ (show $ i + 1) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 28
29. module Main where main :: IO () main = putStrLn $ doStuff 10 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 29
30. -- | take Int, return +1 as text doStuff :: Int -> String doStuff i = "New value: " ++ (show $ i + 1) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 30
31. -- | take Int, return +1 as text doStuff :: Int -> String doStuff i = "New value: " ++ (show $ i + 1) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 31
32. -- | take Int, store it, return +1 as text doStuff :: UUID -> Int -> String doStuff i = ... © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 32
33. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 33
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41. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 41
42. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 42
43. data Storage = Persist UUID Int -- | take Int, store it, return +1 as text doStuff :: UUID -> Int -> (Storage, String) doStuff uuid i = ( Persist uuid newI , "New value: " ++ (show newI) ) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 43
44. data Storage = Persist UUID Int -- | take Int, store it, return +1 as text doStuff :: UUID -> Int -> (Storage, String) doStuff uuid i = ( Persist uuid newI , "New value: " ++ (show newI) ) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 44
45. data Storage = Persist UUID Int -- | take Int, store it, return +1 as text doStuff :: UUID -> Int -> (Storage, String) doStuff uuid i = ( Persist uuid newI , "New value: " ++ (show newI) ) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 45
46. prop_returns_plus1 :: Property prop_returns_plus1 = property $ do -- given i <- Gen.int uuid <- genUUID -- when let result = doStuff uuid i -- then let expected = ( Persist uuid (i + 1) , "New value: " ++ (show $ i + 1) ) result === expected © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 46
47. prop_returns_plus1 :: Property prop_returns_plus1 = property $ do -- given i <- Gen.int uuid <- genUUID -- when let result = doStuff uuid i -- then let expected = ( Persist uuid (i + 1) , "New value: " ++ (show $ i + 1) ) result === expected © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 47
48. prop_returns_plus1 :: Property prop_returns_plus1 = property $ do -- given i <- Gen.int uuid <- genUUID -- when let result = doStuff uuid i -- then let expected = ( Persist uuid (i + 1) , "New value: " ++ (show $ i + 1) ) result === expected © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 48
49. prop_returns_plus1 :: Property prop_returns_plus1 = property $ do -- given i <- Gen.int uuid <- genUUID -- when let result = doStuff uuid i -- then let expected = ( Persist uuid (i + 1) , "New value: " ++ (show $ i + 1) ) result === expected © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 49
50. prop_returns_plus1 :: Property prop_returns_plus1 = property $ do -- given i <- Gen.int uuid <- genUUID -- when let result = doStuff uuid i -- then let expected = ( Persist uuid (i + 1) , "New value: " ++ (show $ i + 1) ) result === expected © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 50
51. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 51
52. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 52
53. doStuff :: UUID -> Int -> (Storage, String) interpret :: (Storage, String) -> IO String © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 53
54. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> (Storage, String) -> IO String interpret ioRef (Persist uuid pi, i) = do modifyIORef ioRef (M.insert uuid pi) return i © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 54
55. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> (Storage, String) -> IO String interpret ioRef (Persist uuid pi, i) = do modifyIORef ioRef (M.insert uuid pi) return i © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 55
56. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> (Storage, String) -> IO String interpret ioRef (Persist uuid pi, i) = do modifyIORef ioRef (M.insert uuid pi) return i © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 56
57. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> (Storage, String) -> IO String interpret ioRef (Persist uuid pi, i) = do modifyIORef ioRef (M.insert uuid pi) return i © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 57
58. main :: IO () main = do ioRef <- newIORef M.empty uuid <- nextRandom res <- interpret ioRef (doStuff uuid 10) putStrLn res © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 58
59. -- | take Int, store it, return +1 as text doStuff :: UUID -> Int -> (Storage, String) doStuff uuid i = ( Persist uuid newI , "New value: " ++ (show newI) ) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 59
60. -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> (Storage, String) doStuff uuid i = ( Persist uuid newI , "New value: " ++ (show newI) ) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 60
61. -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> ([Storage], String) doStuff uuid i = ( [(Persist uuid newI)] , "New value: " ++ (show newI) ) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 61
62. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 62
63. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 63
64. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 64
65. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 65
66. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> (Storage, String) -> IO String interpret ioRef (Persist uuid pi, i) = do modifyIORef ioRef (M.insert uuid pi) return i © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 66
67. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> (Storage, String) -> IO String interpret ioRef (Persist uuid pi, i) = do modifyIORef ioRef (M.insert uuid pi) return i © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 67
68. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> ([Storage], String) -> IO String interpret ioRef (actions, i) = do traverse perform actions return i where perform (Persist uuid pi) = modifyIORef ioRef (M.insert uuid pi) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 68
69. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> ([Storage], String) -> IO String interpret ioRef (actions, i) = do traverse perform actions return i where perform (Persist uuid pi) = modifyIORef ioRef (M.insert uuid pi) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 69
70. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> ([Storage], String) -> IO String interpret ioRef (actions, i) = do traverse perform actions return i where perform (Persist uuid pi) = modifyIORef ioRef (M.insert uuid pi) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 70
71. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> ([Storage], String) -> IO String interpret ioRef (actions, i) = do traverse perform actions return i where perform (Persist uuid pi) = modifyIORef ioRef (M.insert uuid pi) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 71
72. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> ([Storage], String) -> IO String interpret ioRef (actions, i) = do traverse perform actions return i where perform (Persist uuid pi) = modifyIORef ioRef (M.insert uuid pi) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 72
73. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> ([Storage], String) -> IO String interpret ioRef (actions, i) = do traverse perform actions return i where perform (Persist uuid pi) = modifyIORef ioRef (M.insert uuid pi) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 73
74. prop_returns_plus1 :: Property prop_returns_plus1 = property $ do -- given i <- Gen.int uuid <- genUUID -- when let result = doStuff uuid i -- then let expected = ( Persist uuid (i + 1) , "New value: " ++ (show $ i + 1) ) result === expected © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 74
75. prop_returns_plus1 :: Property prop_returns_plus1 = property $ do -- given i <- Gen.int uuid <- genUUID -- when let result = doStuff uuid i -- then let expected = ( [Persist uuid (i + 1)] , "New value: " ++ (show $ i + 1) ) result === expected © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 75
76. main :: IO () main = do ioRef <- newIORef M.empty uuid <- nextRandom res <- interpret ioRef (doStuff uuid 10) putStrLn res © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 76
77. -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> ([Storage], String) doStuff uuid i = ( [(Persist uuid newI)] , "New value: " ++ (show newI) ) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 77
78. -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> ([Storage], String) doStuff uuid i = ( [ (Persist uuid newI) , (Persist uuid newI) ] , "New value: " ++ (show newI) ) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 78
79. prop_returns_plus1 :: Property prop_returns_plus1 = property $ do -- given i <- Gen.int uuid <- genUUID -- when let result = doStuff uuid i -- then let expected = ( [Persist uuid (i + 1)] , "New value: " ++ (show $ i + 1) ) result === expected © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 79
80. prop_returns_plus1 :: Property prop_returns_plus1 = property $ do -- given i <- Gen.int uuid <- genUUID -- when let result = doStuff uuid i -- then let expected = ( [ Persist uuid (i + 1) , Persist uuid (i + 1)] , "New value: " ++ (show $ i + 1) ) result === expected © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 80
81. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 81
82. doStuff :: UUID -> Int -> ([Storage], String) interpret :: ([Storage], String) -> IO String © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 82
83. sthElse :: UUID -> Int -> ([Storage], Int) interpret :: ([Storage], String) -> IO String © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 83
84. sthElse :: UUID -> Int -> ([Storage], Int) interpret :: ([Storage], a) -> IO a © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 84
85. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> ([Storage], String) -> IO String interpret ioRef (actions, i) = do traverse perform actions return i where perform (Persist uuid pi) = modifyIORef ioRef (M.insert uuid pi) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 85
86. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> ([Storage], a) -> IO a interpret ioRef (actions, i) = do traverse perform actions return i where perform (Persist uuid pi) = modifyIORef ioRef (M.insert uuid pi) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 86
87. data Storage k = Persist UUID Int deriving stock (Eq, Show) -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> ([Storage], String) doStuff uuid i = ( [ (Persist uuid newI) , (Persist uuid newI)] , "New value: " ++ (show newI) ) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 87
88. data Storage k = Persist UUID Int deriving stock (Eq, Show) -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> ([Storage], String) doStuff uuid i = ( [ (Persist uuid newI) , (Persist uuid newI)] , "New value: " ++ (show newI) ) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 88
89. data Storage k = Done k | Persist UUID Int deriving stock (Eq, Show) -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> [Storage String] doStuff uuid i = [ (Persist uuid newI) , (Persist uuid newI) , (Done $ "New value: " ++ (show newI))] where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 89
90. data Storage k = Done k | Persist UUID Int deriving stock (Eq, Show) -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> [Storage String] doStuff uuid i = [ (Persist uuid newI) , (Persist uuid newI) , (Done $ "New value: " ++ (show newI))] where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 90
91. data Storage k = Done k | Persist UUID Int deriving stock (Eq, Show) -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> [Storage String] doStuff uuid i = [ (Persist uuid newI) , (Persist uuid newI) , (Done $ "New value: " ++ (show newI))] where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 91
92. data Storage k = Done k | Persist UUID Int deriving stock (Eq, Show) -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> [Storage String] doStuff uuid i = [ (Persist uuid newI) , (Persist uuid newI) , (Done $ "New value: " ++ (show newI))] where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 92
93. interpret :: IORef InMemStorage -> ([Storage], a) -> IO a interpret ioRef (actions, i) = do traverse perform actions return i where perform (Persist uuid pi) = modifyIORef ioRef (M.insert uuid pi) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 93
94. interpret :: IORef InMemStorage -> ([Storage], a) -> IO a interpret ioRef (actions, i) = do traverse perform actions return i where perform (Persist uuid pi) = modifyIORef ioRef (M.insert uuid pi) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 94
95. interpret :: IORef InMemStorage -> [Storage a] -> IO a interpret ioRef actions = do traverse perform (init actions) value (last actions) where perform (Persist uuid pi) = modifyIORef ioRef (M.insert uuid pi) value (Done a) = pure a value _ = fail "failed" © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 95
96. interpret :: IORef InMemStorage -> [Storage a] -> IO a interpret ioRef actions = do traverse perform (init actions) value (last actions) where perform (Persist uuid pi) = modifyIORef ioRef (M.insert uuid pi) value (Done a) = pure a value _ = fail "failed" © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 96
97. interpret :: IORef InMemStorage -> [Storage a] -> IO a interpret ioRef actions = do traverse perform (init actions) value (last actions) where perform (Persist uuid pi) = modifyIORef ioRef (M.insert uuid pi) value (Done a) = pure a value _ = fail "failed" © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 97
98. interpret :: IORef InMemStorage -> [Storage a] -> IO a interpret ioRef actions = do traverse perform (init actions) value (last actions) where perform (Persist uuid pi) = modifyIORef ioRef (M.insert uuid pi) value (Done a) = pure a value _ = fail "failed" © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 98
99. data Storage k = Done k | Persist UUID Int deriving stock (Eq, Show) -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> [Storage String] doStuff uuid i = [ (Persist uuid newI) , (Persist uuid newI) , (Done $ "New value: " ++ (show newI)) ] where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 99
100. data Storage k = Done k | Persist UUID Int (Storage k) deriving stock (Eq, Show) -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> [Storage String] doStuff uuid i = [ (Persist uuid newI) , (Persist uuid newI) , (Done $ "New value: " ++ (show newI)) ] where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 100
101. data Storage k = Done k | Persist UUID Int (Storage k) deriving stock (Eq, Show) -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> [Storage String] doStuff uuid i = [ (Persist uuid newI) , (Persist uuid newI) , (Done $ "New value: " ++ (show newI)) ] where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 101
102. data Storage k = Done k | Persist UUID Int (Storage k) deriving stock (Eq, Show) -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = (Persist uuid newI (Persist uuid newI (Done $ "New value: " ++ (show newI)) )) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 102
103. data Storage k = Done k | Persist UUID Int (Storage k) deriving stock (Eq, Show) -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = (Persist uuid newI (Persist uuid newI (Done $ "New value: " ++ (show newI)) )) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 103
104. data Storage k = Done k | Persist UUID Int (Storage k) deriving stock (Eq, Show) -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = (Persist uuid newI (Persist uuid newI (Done $ "New value: " ++ (show newI)) )) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 104
105. data Storage k = Done k | Persist UUID Int (Storage k) deriving stock (Eq, Show) -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = (Persist uuid newI (Persist uuid newI (Done $ "New value: " ++ (show newI)) )) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 105
106. interpret :: IORef InMemStorage -> Storage a -> IO a interpret ioRef (Done a) = pure a interpret ioRef (Persist uuid i next) = modifyIORef ioRef (M.insert uuid i) *> interpret ioRef next © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 106
107. interpret :: IORef InMemStorage -> Storage a -> IO a interpret ioRef (Done a) = pure a interpret ioRef (Persist uuid i next) = modifyIORef ioRef (M.insert uuid i) *> interpret ioRef next © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 107
108. interpret :: IORef InMemStorage -> Storage a -> IO a interpret ioRef (Done a) = pure a interpret ioRef (Persist uuid i next) = modifyIORef ioRef (M.insert uuid i) *> interpret ioRef next © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 108
109. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 109
110. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 110
111. interpret :: IORef InMemStorage -> Storage a -> IO a interpret ioRef (Done a) = pure a interpret ioRef (Persist uuid i next) = modifyIORef ioRef (M.insert uuid i) *> interpret ioRef next © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 111
112. data Storage k = Done k | Persist UUID Int (Storage k) deriving stock (Eq, Show) -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = (Persist uuid newI (Persist uuid newI (Done $ "New value: " ++ (show newI)) )) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 112
113. data Storage k = Done k | Persist UUID Int (Storage k) deriving stock (Eq, Show) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 113
114. data Storage k = Done k | Persist UUID Int (Storage k) deriving stock (Functor, Eq, Show) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 114
115. data Storage k = Done k | Persist UUID Int (Storage k) deriving stock (Functor, Eq, Show) instance Applicative Storage where pure a = Done a (<*>) func (Done a) = fmap (\f -> f a) func (<*>) func (Persist uuid i next) = Persist uuid i (func <*> next) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 115
116. -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = (Persist uuid newI (Persist uuid newI (Done $ "New value: " ++ (show newI)) )) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 116
117. -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = Persist uuid newI (Done ()) *> Persist uuid newI (Done ()) *> pure ("New value: " ++ (show newI)) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 117
118. -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = Persist uuid newI (Done ()) *> Persist uuid newI (Done ()) *> pure ("New value: " ++ (show newI)) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 118
119. -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = Persist uuid newI (Done ()) *> Persist uuid newI (Done ()) *> pure ("New value: " ++ (show newI)) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 119
120. -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = Persist uuid newI (Done ()) *> Persist uuid newI (Done ()) *> pure ("New value: " ++ (show newI)) where newI = i + 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 120
121. -- | take Int, store it once, story it twice, return +1 as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = persist uuid newI *> persist uuid newI *> pure ("New value: " ++ (show newI)) where newI = i + 1 persist :: UUID -> Int -> Storage () persist uuid i = Persist uuid i (Done ()) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 121
122. -- | take Int, fetch existing Int (if does not exist, default to zero) -- | add them, store the result, return result as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = fetch uuid *> persist ... data Storage k = Done k | Persist UUID Int (Storage k) | Fetch UUID ... deriving stock (Functor) fetch :: UUID -> Storage (Maybe Int) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 122
123. -- | take Int, fetch existing Int (if does not exist, default to zero) -- | add them, store the result, return result as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = fetch uuid *> persist ... data Storage k = Done k | Persist UUID Int (Storage k) | Fetch UUID ... deriving stock (Functor) fetch :: UUID -> Storage (Maybe Int) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 123
124. -- | take Int, fetch existing Int (if does not exist, default to zero) -- | add them, store the result, return result as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = fetch uuid *> persist ... data Storage k = Done k | Persist UUID Int (Storage k) | Fetch UUID ... deriving stock (Functor) fetch :: UUID -> Storage (Maybe Int) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 124
125. -- | take Int, fetch existing Int (if does not exist, default to zero) -- | add them, store the result, return result as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = fetch uuid *> persist ... data Storage k = Done k | Persist UUID Int (Storage k) | Fetch UUID ... deriving stock (Functor) fetch :: UUID -> Storage (Maybe Int) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 125
126. -- | take Int, fetch existing Int (if does not exist, default to zero) -- | add them, store the result, return result as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = fetch uuid *> persist ... data Storage k = Done k | Persist UUID Int (Storage k) | Fetch UUID ... deriving stock (Functor) fetch :: UUID -> Storage (Maybe Int) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 126
127. data Storage k = Done k | Persist UUID Int (Storage k) deriving stock (Functor) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 127
128. data Storage k = Done k | Persist UUID Int (Storage k) | Fetch UUID (Maybe Int -> Storage k) deriving stock (Functor) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 128
129. data Storage k = Done k | Persist UUID Int (Storage k) | Fetch UUID (Maybe Int -> Storage k) deriving stock (Functor) persist :: UUID -> Int -> Storage () persist uuid i = Persist uuid i (Done ()) fetch :: UUID -> Storage (Maybe Int) fetch uuid = Fetch uuid (\mi -> Done mi) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 129
130. data Storage k = Done k | Persist UUID Int (Storage k) | Fetch UUID (Maybe Int -> Storage k) deriving stock (Functor) persist :: UUID -> Int -> Storage () persist uuid i = Persist uuid i (Done ()) fetch :: UUID -> Storage (Maybe Int) fetch uuid = Fetch uuid pure © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 130
131. "Sequen'ally compose two ac'ons, passing any value produced by the first as an argument to the second." © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 131
132. ??? :: m a -> (a -> m b) -> m b © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 132
133. >>= :: m a -> (a -> m b) -> m b © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 133
134. instance Monad Storage where (Done a) >>= f = f a (Persist uuid i next) >>= f = Persist uuid i (next >>= f) (Fetch uuid nextFunc) >>= f = Fetch uuid (\mi -> (nextFunc mi) >>= f) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 134
135. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 135
136. -- | take Int, fetch existing Int -- | (if does not exist, default to zero) -- | add them, -- | store the result, -- | return result as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 136
137. -- | take Int, fetch existing Int -- | (if does not exist, default to zero) -- | add them, -- | store the result, -- | return result as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 137
138. -- | take Int, fetch existing Int -- | (if does not exist, default to zero) -- | add them, -- | store the result, -- | return result as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 138
139. -- | take Int, fetch existing Int -- | (if does not exist, default to zero) -- | add them, -- | store the result, -- | return result as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 139
140. -- | take Int, fetch existing Int -- | (if does not exist, default to zero) -- | add them, -- | store the result, -- | return result as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 140
141. -- | take Int, fetch existing Int -- | (if does not exist, default to zero) -- | add them, -- | store the result, -- | return result as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 141
142. -- | take Int, fetch existing Int -- | (if does not exist, default to zero) -- | add them, -- | store the result, -- | return result as text doStuff :: UUID -> Int -> Storage String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 142
143. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> Storage a -> IO a interpret ioRef (Done a) = pure a interpret ioRef (Persist uuid i next) = (modifyIORef ioRef (M.insert uuid i)) *> (interpret ioRef next) interpret ioRef (Fetch uuid nextFunc) = do inmem <- readIORef ioRef let maybeI = M.lookup uuid inmem interpret ioRef (nextFunc maybeI) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 143
144. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> Storage a -> IO a interpret ioRef (Done a) = pure a interpret ioRef (Persist uuid i next) = (modifyIORef ioRef (M.insert uuid i)) *> (interpret ioRef next) interpret ioRef (Fetch uuid nextFunc) = do inmem <- readIORef ioRef let maybeI = M.lookup uuid inmem interpret ioRef (nextFunc maybeI) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 144
145. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> Storage a -> IO a interpret ioRef (Done a) = pure a interpret ioRef (Persist uuid i next) = (modifyIORef ioRef (M.insert uuid i)) *> (interpret ioRef next) interpret ioRef (Fetch uuid nextFunc) = do inmem <- readIORef ioRef let maybeI = M.lookup uuid inmem interpret ioRef (nextFunc maybeI) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 145
146. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> Storage a -> IO a interpret ioRef (Done a) = pure a interpret ioRef (Persist uuid i next) = (modifyIORef ioRef (M.insert uuid i)) *> (interpret ioRef next) interpret ioRef (Fetch uuid nextFunc) = do inmem <- readIORef ioRef let maybeI = M.lookup uuid inmem interpret ioRef (nextFunc maybeI) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 146
147. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> Storage a -> IO a interpret ioRef (Done a) = pure a interpret ioRef (Persist uuid i next) = (modifyIORef ioRef (M.insert uuid i)) *> (interpret ioRef next) interpret ioRef (Fetch uuid nextFunc) = do inmem <- readIORef ioRef let maybeI = M.lookup uuid inmem interpret ioRef (nextFunc maybeI) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 147
148. type InMemStorage = M.Map UUID Int interpret :: IORef InMemStorage -> Storage a -> IO a interpret ioRef (Done a) = pure a interpret ioRef (Persist uuid i next) = (modifyIORef ioRef (M.insert uuid i)) *> (interpret ioRef next) interpret ioRef (Fetch uuid nextFunc) = do inmem <- readIORef ioRef let maybeI = M.lookup uuid inmem interpret ioRef (nextFunc maybeI) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 148
149. prop_fetch_add_store_return :: Property prop_fetch_add_store_return = property $ do -- given i <- Gen.int uuid <- genUUID initial <- Gen.int ioRef <- evalIO $ newIORef $ M.singleton uuid initial -- when res <- evalIO $ interpret ioRef (doStuff uuid i) -- then inmem <- evalIO $ readIORef ioRef res === "New value: " ++ show (i + initial) M.toList inmem === [(uuid, i + initial)] © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 149
150. doStuff :: UUID -> Int -> IO String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 150
151. doStuff :: UUID -> Int -> Storage String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 151
152. data Storage k = Done k | Persist UUID Int (Storage k) | Fetch UUID (Maybe Int -> Storage k) deriving stock (Functor) instance Applicative Storage where pure a = Done a (<*>) func (Done a) = fmap (\f -> f a) func (<*>) func (Persist uuid i next) = Persist uuid i (func <*> next) instance Monad Storage where (Done a) >>= f = f a (Persist uuid i next) >>= f = Persist uuid i (next >>= f) (Fetch uuid nextFunc) >>= f = Fetch uuid (\mi -> (nextFunc mi) >>= f) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 152
153. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 153
154. data Storage k = Done k | Persist UUID Int (Storage k) | Fetch UUID (Maybe Int -> Storage k) deriving stock (Functor) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 154
155. data Storage k = Persist UUID Int k | Fetch UUID (Maybe Int -> k) deriving stock (Functor) data Free (f:: * -> *) (k :: *) = Pure k | Impure (f (Free f k)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 155
156. data Storage k = Persist UUID Int k | Fetch UUID (Maybe Int -> k) deriving stock (Functor) data Free (f:: * -> *) (k :: *) = Pure k | Impure (f (Free f k)) persist :: UUID -> Int -> Free Storage () persist uuid i = Impure (Persist uuid i (Pure ())) fetch :: UUID -> Free Storage (Maybe Int) fetch uuid = Impure (Fetch uuid (\mi -> Pure mi)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 156
157. instance Functor f => Functor (Free f) where fmap f (Pure k) = Pure $ f k fmap f (Impure c) = Impure (fmap (fmap f) c) instance Functor f => Applicative (Free f) where pure a = Pure a (<*>) func (Pure a) = fmap (\f -> f a) func (<*>) func (Impure c) = Impure (fmap (\f -> func <*> f) c) instance Functor f => Monad (Free f) where Pure k >>= f = f k Impure c >>= f = Impure $ fmap (\x -> x >>= f) c © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 157
158. data Storage k = Persist UUID Int k | Fetch UUID (Maybe Int -> k) deriving stock (Functor) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 158
159. doStuff :: UUID -> Int -> Storage String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 159
160. doStuff :: UUID -> Int -> Free Storage String doStuff uuid i = do maybeOld <- fetch uuid let oldI = maybe 0 id maybeOld newI = oldI + i persist uuid newI pure ("New value: " ++ (show newI)) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 160
161. interpretFree :: Monad m => (forall x. f x -> m x) -> Free f a -> m a interpretFree _ (Pure a) = pure a interpretFree f (Impure c) = f c >>= interpretFree f © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 161
162. interpretFree :: Monad m => (forall x. f x -> m x) -> Free f a -> m a interpretFree _ (Pure a) = pure a interpretFree f (Impure c) = f c >>= interpretFree f interpret :: IORef InMemStorage -> Storage a -> IO a interpret ioRef (Persist uuid i k) = do modifyIORef ioRef (M.insert uuid i) pure k interpret ioRef (Fetch uuid kFunc) = do inmem <- readIORef ioRef let maybeI = M.lookup uuid inmem pure $ kFunc maybeI © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 162
163. interpretFree :: Monad m => (forall x. f x -> m x) -> Free f a -> m a interpretFree _ (Pure a) = pure a interpretFree f (Impure c) = f c >>= interpretFree f interpret :: IORef InMemStorage -> Storage a -> IO a interpret ioRef (Persist uuid i k) = do modifyIORef ioRef (M.insert uuid i) pure k interpret ioRef (Fetch uuid kFunc) = do inmem <- readIORef ioRef let maybeI = M.lookup uuid inmem pure $ kFunc maybeI © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 163
164. interpretFree :: Monad m => (forall x. f x -> m x) -> Free f a -> m a interpretFree _ (Pure a) = pure a interpretFree f (Impure c) = f c >>= interpretFree f interpret :: IORef InMemStorage -> Storage a -> IO a interpret ioRef (Persist uuid i k) = do modifyIORef ioRef (M.insert uuid i) pure k interpret ioRef (Fetch uuid kFunc) = do inmem <- readIORef ioRef let maybeI = M.lookup uuid inmem pure $ kFunc maybeI © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 164
165. interpretFree :: Monad m => (forall x. f x -> m x) -> Free f a -> m a interpretFree _ (Pure a) = pure a interpretFree f (Impure c) = f c >>= interpretFree f interpret :: IORef InMemStorage -> Storage a -> IO a interpret ioRef (Persist uuid i k) = do modifyIORef ioRef (M.insert uuid i) pure k interpret ioRef (Fetch uuid kFunc) = do inmem <- readIORef ioRef let maybeI = M.lookup uuid inmem pure $ kFunc maybeI © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 165
166. interpretFree :: (f x -> m x) -> Free f a -> m a interpret :: IORef InMemStorage -> Storage a -> IO a © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 166
167. prop_fetch_add_store_return :: Property prop_fetch_add_store_return = property $ do -- given i <- Gen.int uuid <- genUUID initial <- Gen.int ioRef <- evalIO $ newIORef $ M.singleton uuid initial -- when res <- evalIO $ interpret ioRef (doStuff uuid i) -- then inmem <- evalIO $ readIORef ioRef res === "New value: " ++ show (i + initial) M.toList inmem === [(uuid, i + initial)] © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 167
168. prop_fetch_add_store_return :: Property prop_fetch_add_store_return = property $ do -- given i <- Gen.int uuid <- genUUID initial <- Gen.int ioRef <- evalIO $ newIORef $ M.singleton uuid initial -- when res <- evalIO $ interpret ioRef (doStuff uuid i) -- then inmem <- evalIO $ readIORef ioRef res === "New value: " ++ show (i + initial) M.toList inmem === [(uuid, i + initial)] © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 168
169. prop_fetch_add_store_return :: Property prop_fetch_add_store_return = property $ do -- given i <- Gen.int uuid <- genUUID initial <- Gen.int ioRef <- evalIO $ newIORef $ M.singleton uuid initial -- when res <- evalIO $ interpretFree (interpret ioRef) (doStuff uuid i) -- then inmem <- evalIO $ readIORef ioRef res === "New value: " ++ show (i + initial) M.toList inmem === [(uuid, i + initial)] © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 169
170. Free Monads? © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 170
171. "As a Billing System user I want to generate an invoice for a given account based on its current system use" © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 171
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185. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 185
186. To generate invoice for account account_id 1. fetch profile from CRM 2. fetch CDRs from FTP 3. generate invoice number 4. total = sum cdrs 5. glue together © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 186
187. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 187
188. h"ps:/ /github.com/polysemy-research/polysemy © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 188
189. Sem r a . program :: Sem '[Console, (Random Int)] Int © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 189
190. Sem r a . program :: Sem '[Console, (Random Int)] Int © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 190
191. Sem r a . program :: Sem '[Console, (Random Int)] Int © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 191
192. Sem r a ___ program :: Sem '[Console, (Random Int)] Int ___ .________________________________________^ © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 192
193. Sem r a . program :: Sem '[Console, (Random Int)] Int © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 193
194. Sem r a ________________________ program :: Sem '[Console, (Random Int)] Int ________________________ .________________________^ © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 194
195. Sem r a . program :: Sem '[Console, (Random Int)] Int © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 195
196. Sem r a program :: Member Console r => Member (Random Int) r => Sem r Int . © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 196
197. Sem r a program :: Member Console r => Member (Random Int) r => Sem r Int .________^ © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 197
198. Sem r a program :: Member Console r <| => Member (Random Int) r <| => Sem r Int | .________^_____________________| © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 198
199. program :: Member Console r => Member (Random Int) r => Sem r Int data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String makeSem ''Console printLine :: Member Console r => String -> Sem r () readLine :: Member Console r => Sem r String © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 199
200. program :: Member Console r => Member (Random Int) r => Sem r Int data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String makeSem ''Console printLine :: Member Console r => String -> Sem r () readLine :: Member Console r => Sem r String © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 200
201. program :: Member Console r => Member (Random Int) r => Sem r Int data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String makeSem ''Console printLine :: Member Console r => String -> Sem r () readLine :: Member Console r => Sem r String © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 201
202. program :: Member Console r => Member (Random Int) r => Sem r Int data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String makeSem ''Console printLine :: Member Console r => String -> Sem r () readLine :: Member Console r => Sem r String © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 202
203. program :: Member Console r => Member (Random Int) r => Sem r Int data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String makeSem ''Console printLine :: Member Console r => String -> Sem r () readLine :: Member Console r => Sem r String © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 203
204. program :: Member Console r => Member (Random Int) r => Sem r Int data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String makeSem ''Console printLine :: Member Console r => String -> Sem r () readLine :: Member Console r => Sem r String © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 204
205. program :: Member Console r => Member (Random Int) r => Sem r Int data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String makeSem ''Console printLine :: Member Console r => String -> Sem r () readLine :: Member Console r => Sem r String © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 205
206. program :: Member Console r => Member (Random Int) r => Sem r Int data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String makeSem ''Console printLine :: Member Console r => String -> Sem r () readLine :: Member Console r => Sem r String © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 206
207. program :: Member Console r => Member (Random Int) r => Sem r Int data Random v m a where NextRandom :: Random v m v makeSem ''Random nextRandom :: Member (Random v) r => Sem r v © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 207
208. program :: Member Console r => Member (Random Int) r => Sem r Int data Random v m a where NextRandom :: Random v m v makeSem ''Random nextRandom :: Member (Random v) r => Sem r v © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 208
209. program :: Member Console r => Member (Random Int) r => Sem r Int data Random v m a where NextRandom :: Random v m v makeSem ''Random nextRandom :: Member (Random v) r => Sem r v © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 209
210. program :: Member Console r => Member (Random Int) r => Sem r Int data Random v m a where NextRandom :: Random v m v makeSem ''Random nextRandom :: Member (Random v) r => Sem r v © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 210
211. -- cheatsheet printLine :: Member Console r => String -> Sem r () readLine :: Member Console r => Sem r String nextRandom :: Member (Random v) r => Sem r v program :: Member Console r => Member (Random Int) r => Sem r Int program = do printLine "Insert your number:" i1 <- readLine i2 <- nextRandom pure (read i1 + i2) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 211
212. -- cheatsheet printLine :: Member Console r => String -> Sem r () readLine :: Member Console r => Sem r String nextRandom :: Member (Random v) r => Sem r v program :: Member Console r => Member (Random Int) r => Sem r Int program = do printLine "Insert your number:" i1 <- readLine i2 <- nextRandom pure (read i1 + i2) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 212
213. -- cheatsheet printLine :: Member Console r => String -> Sem r () readLine :: Member Console r => Sem r String nextRandom :: Member (Random v) r => Sem r v program :: Member Console r => Member (Random Int) r => Sem r Int program = do printLine "Insert your number:" i1 <- readLine i2 <- nextRandom pure (read i1 + i2) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 213
214. -- cheatsheet printLine :: Member Console r => String -> Sem r () readLine :: Member Console r => Sem r String nextRandom :: Member (Random v) r => Sem r v program :: Member Console r => Member (Random Int) r => Sem r Int program = do printLine "Insert your number:" i1 <- readLine i2 <- nextRandom pure (read i1 + i2) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 214
215. -- cheatsheet printLine :: Member Console r => String -> Sem r () readLine :: Member Console r => Sem r String nextRandom :: Member (Random v) r => Sem r v program :: Member Console r => Member (Random Int) r => Sem r Int program = do printLine "Insert your number:" i1 <- readLine i2 <- nextRandom pure (read i1 + i2) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 215
216. -- cheatsheet printLine :: Member Console r => String -> Sem r () readLine :: Member Console r => Sem r String nextRandom :: Member (Random v) r => Sem r v program :: Member Console r => Member (Random Int) r => Sem r Int program = do printLine "Insert your number:" i1 <- readLine i2 <- nextRandom pure (read i1 + i2) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 216
217. program :: Member Console r => Member (Random Int) r => Sem r Int program = do printLine "Insert your number:" i1 <- readLine i2 <- nextRandom pure (read i1 + i2) -- Sem r a ~> IO a ? © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 217
218. run :: Sem '[] a -> a runM :: Monad m => Sem '[Embed m] a -> m a -- Sem '[Embed IO] a -> IO a program :: Member Console r => Member (Random Int) r => Sem r Int -- Sem '[Console, Random Int] Int © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 218
219. run :: Sem '[] a -> a runM :: Monad m => Sem '[Embed m] a -> m a -- Sem '[Embed IO] a -> IO a program :: Member Console r => Member (Random Int) r => Sem r Int -- Sem '[Console, Random Int] Int © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 219
220. run :: Sem '[] a -> a runM :: Monad m => Sem '[Embed m] a -> m a -- Sem '[Embed IO] a -> IO a program :: Member Console r => Member (Random Int) r => Sem r Int -- Sem '[Console, Random Int] Int © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 220
221. run :: Sem '[] a -> a runM :: Monad m => Sem '[Embed m] a -> m a -- Sem '[Embed IO] a -> IO a program :: Member Console r => Member (Random Int) r => Sem r Int -- Sem '[Console, Random Int] Int © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 221
222. run :: Sem '[] a -> a runM :: Monad m => Sem '[Embed m] a -> m a -- Sem '[Embed IO] a -> IO a program :: Member Console r => Member (Random Int) r => Sem r Int -- Sem '[Console, Random Int] Int © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 222
223. What we need is an interpreter © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 223
224. data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String runConsoleIO :: Member (Embed IO) r => Sem (Console ': r) a -> Sem r a runConsoleIO = interpret $ \case PrintLine line -> putStrLn line ReadLine -> getLine © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 224
225. data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String runConsoleIO :: Member (Embed IO) r => Sem (Console ': r) a -> Sem r a runConsoleIO = interpret $ \case PrintLine line -> putStrLn line ReadLine -> getLine © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 225
226. data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String runConsoleIO :: Member (Embed IO) r => Sem (Console ': r) a -> Sem r a runConsoleIO = interpret $ \case PrintLine line -> putStrLn line ReadLine -> getLine © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 226
227. data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String runConsoleIO :: Member (Embed IO) r => Sem (Console ': r) a -> Sem r a runConsoleIO = interpret $ \case PrintLine line -> putStrLn line ReadLine -> getLine © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 227
228. data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String runConsoleIO :: Member (Embed IO) r => Sem (Console ': r) a -> Sem r a runConsoleIO = interpret $ \case PrintLine line -> putStrLn line ReadLine -> getLine © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 228
229. data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String runConsoleIO :: Member (Embed IO) r => Sem (Console ': r) a -> Sem r a runConsoleIO = interpret $ \case PrintLine line -> putStrLn line ReadLine -> getLine © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 229
230. data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String -- embed :: Member (Embed m) r => m a -> Sem r a runConsoleIO :: Member (Embed IO) r => Sem (Console ': r) a -> Sem r a runConsoleIO = interpret $ \case PrintLine line -> putStrLn line ReadLine -> getLine © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 230
231. data Console m a where PrintLine :: String -> Console m () ReadLine :: Console m String -- embed :: Member (Embed m) r => m a -> Sem r a runConsoleIO :: Member (Embed IO) r => Sem (Console ': r) a -> Sem r a runConsoleIO = interpret $ \case PrintLine line -> embed $ putStrLn line ReadLine -> embed $ getLine © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 231
232. data Random v m a where NextRandom :: Random v m v runRandomIO :: Member (Embed IO) r => Sem (Random Int ': r) a -> Sem r a runRandomIO = interpret $ \case NextRandom -> embed randomIO © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 232
233. data Random v m a where NextRandom :: Random v m v runRandomIO :: Member (Embed IO) r => Sem (Random Int ': r) a -> Sem r a runRandomIO = interpret $ \case NextRandom -> embed randomIO © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 233
234. main :: IO () main = execute >>= putStrLn.show where execute = program & runConsoleIO & runRandomIO & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 234
235. main :: IO () main = execute >>= putStrLn.show where execute = program -- Sem '[Console, Random Int ] Int & runConsoleIO & runRandomIO & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 235
236. main :: IO () main = execute >>= putStrLn.show where execute = program -- Sem '[Console, Random Int ] Int & runConsoleIO -- Sem '[ , Random Int, Embed IO] Int & runRandomIO & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 236
237. main :: IO () main = execute >>= putStrLn.show where execute = program -- Sem '[Console, Random Int ] Int & runConsoleIO -- Sem '[ , Random Int, Embed IO] Int & runRandomIO -- Sem '[ , Embed IO] Int & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 237
238. main :: IO () main = execute >>= putStrLn.show where execute = program -- Sem '[Console, Random Int ] Int & runConsoleIO -- Sem '[ , Random Int, Embed IO] Int & runRandomIO -- Sem '[ , Embed IO] Int & runM -- IO Int © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 238
239. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 239
240. data Invoice = Invoice { invoiceNumber :: InvoiceNumber , fullName :: FullName , deliveryAddress :: Address , total :: Cent } © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 240
241. newtype InvoiceNumber = InvoiceNumber { unInvoiceNumber :: Text } deriving (Show, Eq) data Address = Address { street :: Text , house :: Text , num :: Text , city :: Text , country :: Text } data FullName = FullName { first :: Text , last :: Text } © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 241
242. data Invoice = Invoice { invoiceNumber :: InvoiceNumber , fullName :: FullName , deliveryAddress :: Address , total :: Cent } © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 242
243. data CallType = Voice | Sms newtype Duration = Duration { unDuration :: Int } deriving stock (Show, Eq) deriving newtype (Num) data Cdr = Cdr { uuid :: UUID , accountId :: AccountId , callType :: CallType , callDuration :: Duration } © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 243
244. data Plan = Plan { voiceCost :: Cent , smsCost :: Cent } data Profile = Profile { firstName :: Text , lastName :: Text , address :: Address , plan :: Plan } © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 244
245. mkInvoice :: InvoiceNumber -> Profile -> [Cdr] -> Invoice mkInvoice invNum Profile {..} cdrs = Invoice { invoiceNumber = invNum , fullName = FullName firstName lastName , deliveryAddress= address , total = foldr cost zeroCents cdrs } where cost (Cdr _ _ Voice (Duration duration)) acc = acc + (voiceCost plan * duration) cost (Cdr _ _ Sms (Duration amount)) acc = acc + (smsCost plan * amount) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 245
246. mkInvoice :: InvoiceNumber -> Profile -> [Cdr] -> Invoice mkInvoice = ... © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 246
247. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 247
248. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 248
249. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 249
250. import Polysemy data Crm m a where GetProfile :: AccountId -> Crm m Profile makeSem ''Crm © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 250
251. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 251
252. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 252
253. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 253
254. import Polysemy data CdrStore m a where FetchCdrs :: AccountId -> CdrStore m [Cdr] makeSem ''CdrStore © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 254
255. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 255
256. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 256
257. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 257
258. import Polysemy data InvoiceStore m a where GenNextInvoiceNumber :: AccountId -> InvoiceStore m InvoiceNumber makeSem ''InvoiceStore © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 258
259. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 259
260. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 260
261. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 261
262. import Polysemy data InvoiceStore m a where GenNextInvoiceNumber :: AccountId -> InvoiceStore m InvoiceNumber makeSem ''InvoiceStore © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 262
263. import Polysemy data InvoiceStore m a where GenNextInvoiceNumber :: AccountId -> InvoiceStore m InvoiceNumber StoreInvoice :: AccountId -> Invoice -> InvoiceStore m () makeSem ''InvoiceStore © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 263
264. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 264
265. © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 265
266. generateInvoice :: Member CdrStore r => Member Crm r => Member InvoiceStore r => AccountId -> Sem r Invoice generateInvoice accId = do invNumber <- genNextInvoiceNumber accId profile <- getProfile accId cdrs <- fetchCdrs accId let invoice = mkInvoice invNumber profile cdrs storeInvoice accId invoice return invoice © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 266
267. data Crm m a where GetProfile :: AccountId -> Crm m Profile type CrmMap = M.Map AccountId Profile runCrm :: Member (State CrmMap) r => Sem (Crm ': r) a -> Sem r a runCrm = interpret $ \case GetProfile accountId -> gets (\m -> m M.! accountId) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 267
268. data CdrStore m a where FetchCdrs :: AccountId -> CdrStore m [Cdr] type CdrMap = M.Map AccountId [Cdr] runCdrStore :: Member (State CdrMap) r => Sem (CdrStore ': r) a -> Sem r a runCdrStore = interpret $ \case FetchCdrs accountId -> gets (\m -> m M.! accountId) © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 268
269. data InvoiceStore m a where StoreInvoice :: AccountId -> Invoice -> InvoiceStore m () GenNextInvoiceNumber :: AccountId -> InvoiceStore m InvoiceNumber type InvoiceMap = M.Map (AccountId, InvoiceNumber) Invoice runInvoiceStore :: Member (State InvoiceMap) r => Member (Embed IO) r => Sem (InvoiceStore ': r) a -> Sem r a runInvoiceStore = interpret $ \case StoreInvoice accountId invoice -> modify (M.insert (accountId, invoiceNumber invoice) invoice) GenNextInvoiceNumber accountId -> embed $ fmap (InvoiceNumber . toText) nextRandom © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 269
270. main :: IO () main = execute where accountId = AccountId 1000 execute = generateInvoice accountId & runCrm & runCdrStore & runInvoiceStore & evalState @CrmMap (M.singleton accountId profile) & evalState @CdrMap (M.singleton accountId (cdrs accountId)) & evalState @InvoiceMap M.empty & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 270
271. main :: IO () main = execute where accountId = AccountId 1000 execute = generateInvoice accountId & runCrm & runCdrStore & runInvoiceStore & evalState @CrmMap (M.singleton accountId profile) & evalState @CdrMap (M.singleton accountId (cdrs accountId)) & evalState @InvoiceMap M.empty & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 271
272. main :: IO () main = execute where accountId = AccountId 1000 execute = generateInvoice accountId & runCrm & runCdrStore & runInvoiceStore & evalState @CrmMap (M.singleton accountId profile) & evalState @CdrMap (M.singleton accountId (cdrs accountId)) & evalState @InvoiceMap M.empty & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 272
273. main :: IO () main = execute where accountId = AccountId 1000 execute = generateInvoice accountId & runCrm & runCdrStore & runInvoiceStore & evalState @CrmMap (M.singleton accountId profile) & evalState @CdrMap (M.singleton accountId (cdrs accountId)) & evalState @InvoiceMap M.empty & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 273
274. main :: IO () main = execute where accountId = AccountId 1000 execute = generateInvoice accountId & runCrm & runCdrStore & runInvoiceStore & evalState @CrmMap (M.singleton accountId profile) & evalState @CdrMap (M.singleton accountId (cdrs accountId)) & evalState @InvoiceMap M.empty & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 274
275. profile :: Profile profile = Profile "John" "Smith" address plan where address = Address "Backer Street" "221b" "2" "London" "United Kingdom" plan = Plan 10 1 © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 275
276. main :: IO () main = execute where accountId = AccountId 1000 execute = generateInvoice accountId & runCrm & runCdrStore & runInvoiceStore & evalState @CrmMap (M.singleton accountId profile) & evalState @CdrMap (M.singleton accountId (cdrs accountId)) & evalState @InvoiceMap M.empty & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 276
277. main :: IO () main = execute where accountId = AccountId 1000 execute = generateInvoice accountId & runCrm & runCdrStore & runInvoiceStore & evalState @CrmMap (M.singleton accountId profile) & evalState @CdrMap (M.singleton accountId (cdrs accountId)) & evalState @InvoiceMap M.empty & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 277
278. cdrs :: AccountId -> [Cdr] cdrs accountId = [ cdr "8abbe08f-4b64-4263-b000-13f3ff77a0c6" Voice 10 , cdr "bed067b0-3e79-429d-8b96-d1f2c96e79ba" Sms 1 , cdr "d4bea3d9-a2a7-44cc-8a8d-301051860761" Voice 30 ] © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 278
279. main :: IO () main = execute where accountId = AccountId 1000 execute = generateInvoice accountId & runCrm & runCdrStore & runInvoiceStore & evalState @CrmMap (M.singleton accountId profile) & evalState @CdrMap (M.singleton accountId (cdrs accountId)) & evalState @InvoiceMap M.empty & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 279
280. main :: IO () main = execute where accountId = AccountId 1000 execute = generateInvoice accountId & runCrm & runCdrStore & runInvoiceStore & evalState @CrmMap (M.singleton accountId profile) & evalState @CdrMap (M.singleton accountId (cdrs accountId)) & evalState @InvoiceMap M.empty & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 280
281. main :: IO () main = execute where accountId = AccountId 1000 execute = generateInvoice accountId & runCrm & runCdrStore & runInvoiceStore & evalState @CrmMap (M.singleton accountId profile) & evalState @CdrMap (M.singleton accountId (cdrs accountId)) & evalState @InvoiceMap M.empty & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 281
282. main :: IO () main = execute where accountId = AccountId 1000 execute = generateInvoice accountId & runCrm & runCdrStore & runInvoiceStore & evalState @CrmMap (M.singleton accountId profile) & evalState @CdrMap (M.singleton accountId (cdrs accountId)) & evalState @InvoiceMap M.empty & runM © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 282
283. main :: IO () main = execute >>= putStrLn.prettyPrint where accountId = AccountId 1000 execute = generateInvoice accountId & runCrm & runCdrStore & runInvoiceStore & evalState @CrmMap (M.singleton accountId profile) & evalState @CdrMap (M.singleton accountId (cdrs accountId)) & evalState @InvoiceMap M.empty & runM prettyPrint = unpack.toStrict.encodePretty © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 283
284. { "fullName": { "first": "John", "last": "Smith" }, "deliveryAddress": { "country": "United Kingdom", "num": "2", "street": "Backer Street", "house": "221b", "city": "London" }, "invoiceNumber": "136172ef-95cb-4714-924a-4d3f9c5e5fd6", "total": 401 } © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 284
285. Maintainable? © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 285
286. Thank You! Pawel Szulc twi$er: @EncodePanda email: paul.szulc@gmail.com © Pawel Szulc, @EncodePanda, paul.szulc@gmail.com 286