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Monadic Computation in Swift. Why? UA Mobile 2017.
This document discusses monadic computation and how it can be used to handle errors and compose functions. It presents a game called MAD.A.DAM to demonstrate how operations like multiplication, addition, and division can fail. It then shows how to implement these operations using a Result monad to propagate errors in a composable way. Finally, it discusses how async operations can also be modeled as a monad to guarantee order of execution and handle failures.
Monadic Computation in Swift. Why? UA Mobile 2017.
- 1. TITLE IN CAPITAL LETTERS VIJAYAP. KANDEL @kandelvijaya iOS Engineer Why Monadic computation?
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- 3. 3 When does itend? 1 more feature
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- 5. 5 Problems 1. Composability 2. Errorpropagation 3. True Type signature
- 6. 6 World full offailing cases (PROBLEM) Verify Monad propagates error and composes 2 Programming Paradigms Deducing answer from Monad Coding the Monad TABLE OF CONTENTS
- 7. 7 Are you connected? IsWifi working? A world of 2 possibilities.
- 8. 8 How do wehandle failable computation?
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- 10. 10 A simple game:MAD.A.DAM 1. M: Multiply input to a random Int 2. A: Add input to a random Int 3. D: Divide input by a random Int 4. Assume Swift doesn’t have Optional Perform: MAD.A.DAM on a dice roll input.
- 11. 11 A simple game:MAD.A.DAM
- 12. 12 A simple game:MAD.A.DAM
- 13. 13 A simple game:MAD.A.DAM
- 14. 14 A simple game:MAD.A.DAM
- 15. 15 A simple game:MAD.A.DAM
- 16. 16 A simple game:MAD.A.DAM
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- 18. 18 Contextual Box T Error Result<T>Contextual Box
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- 29. 29 RESULT MONAD T map flatMap T ->U U T -> U U Monad is a Contextual Type that provides linear binding and composition along with error propagation.
- 30. Monad is aCONTEXTUAL TYPE that provides easy BINDING/COMPOSITION without sacrificing Error Handling.
- 31. 31 RESULT MONAD T map flatMap T ->U U T -> U U Optional<T> is a monad. That is why we can chain stuff together. - map() - flatMap()
- 32. 32 RESULT MONAD T map flatMap T ->U U T -> U U Collection<T> is a monad. - map() - flatMap()
- 33. 33 RESULT MONAD T map flatMap T ->U U T -> U U Swift Try/Catch in principle can be implemented in terms of a Result Monad.
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- 39. 39 Verification: Composability Who careserror handling Solution! I Do! Monadic Solution!
- 40. 40 WAIT, What aboutthe async task that might fail?
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- 43. 43 Promise / Future/ Deferred / IO :: Monad aTask: ( ( (T) -> Void)? -> Void )? T aTask T
- 44. 44 Promise / Future/ Deferred / IO :: Monad aTask: ( ( (T) -> Void)? -> Void )? aTask T then/mapT -> U aTaskaTask T U T -> U
- 45. 45 Promise / Future/ Deferred / IO :: Monad aTask: ( ( (T) -> Void)? -> Void )? aTask T bind/ flatMapT -> Promise<U> aTaskaTask T U T -> U
- 46. 46 Promise / Future/ Deferred / IO :: Monad aTaskaTask T U Evaluate and finally call into outer (U -> Void) By intending to evaluate the inner block and calling into outer block with eventual value; we unpack a promise. None of the Pomise are evaluated unless someone calls `execute()` on the outermost layer. Thereby guarantee of order of execution is applied.
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- 54. 54 A good programmeris someone who looks both ways before crossing a one-way street.” — Doug Linder
- 55. 55 References 1. Monad ResearchPaper http://homepages.inf.ed.ac.uk/wadler/papers/marktoberdorf/baast ad.pdf 2. Railway Oriented Programming https://fsharpforfunandprofit.com/rop/ 3. Dr. Bartosz Category theory lecture https://www.youtube.com/user/DrBartosz/videos 4. My blog for more detailed explanation https://kandelvijaya.com/2017/08/13/promisein30lines/ 5. Promise<T> from the talk https://github.com/kandelvijaya/MPromise 6. Result<T> from the talk https://github.com/kandelvijaya/ResultType
- 56. This presentation andits contents are strictly confidential. It may not, in whole or in part, be reproduced, redistributed, published or passed on to any other person by the recipient. The information in this presentation has not been independently verified. No representation or warranty, express or implied, is made as to the accuracy or completeness of the presentation and the information contained herein and no reliance should be placed on such information. No responsibility is accepted for any liability for any loss howsoever arising, directly or indirectly, from this presentation or its contents. DISCLAIMER 56
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