A presentation at Grammarly Meetup in in Kyiv, Ukraine, 02000 by Anton Pets
How FP made Grammarly codebase error-Free & Predictable Anton Pets 1 October 2019
Grammarly - a writing assistant that helps make your communication clear and effective, wherever you type. 3
Grammarly - a writing assistant that helps make your communication clear and effective, wherever you type. 20M Daily Active Users 4
! Kyiv hiring! ” San Francisco, New York # Vancouver new! 5
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Grammarly Challenges 8
Text is difficult 9
Change is difficult ➡ 10
Our combo Object Oriented Design 11
Our combo Object Oriented Design 12
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TypeScript is… Args validation - free & out of the box 14
TypeScript is… 15
TypeScript is… 💚 16
TypeScript is… Confident refactoring 17
TypeScript is… Interfaces! 18
= ❤ Types + 19
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TypeScript FP libs Funfix fp-ts 23
TypeScript FP libs Funfix fp-ts 24
Functional Programming: Real Life Cases 25
💼 Case 1/4 26
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🧪 How to experiment ? 31
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Can we 🧪 better ? 36
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Pure Functions Deterministic: Same Input ➡ Same output No uncontrolled side effects 46
Pure Functions Deterministic: Same Input ➡ Same output No uncontrolled side effects 47
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⛳ What we achieved 49
⛳ Reliable almost nobody knows about 🧪 50
⛳ Extensible add ♾ number of 🧪 51
💼 Case 2/4 52
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🙏 Will not compile 58
🤔 But how to deal with null? 59
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🤔 Empty alert? Exception? … 61
Bad 62
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Option ≡ an array with 0…1 elements 69
map filter forEach contains … 70
map filter forEach contains … empty getOrElse fold … 71
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⛳ What we achieved 77
⛳ Reliable empty values are safe 78
⛳ Clean no ifs overload, empty values handled separately 79
💼 Case 3/4 80
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🤔 How to handle errors correctly? 94
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⛳ What we achieved 101
⛳ Clean & Confident no defensive programming 102
⛳ Single Responsibility Business logics is separated from error handling 103
💼 Case 4/4 104
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React lazy loading 👍 108
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https://dev.to
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🤔 How to build a good retry function?
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fp-ts 127
Promise in FP Task 128
Promise in FP Task 129
Promise in FP Task 130
Error + Result container Either<Error, Result> 131
Error + Result container Either<Error, Result> 132
Error + Result container Either<Error, React.Component> where type Error = TimeoutError | 404Error 133
Task returning Either Task<Either<Error, Result>> alias: TaskEither<Error, Result> 134
Task returning Either Task<Either<Error, Result>> () => Promise< Either<Error, Result> > 135
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https://github.com/gcanti/retry-ts by the author of fp-ts 139
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You can’t just stop speaking about FP
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Сode examples: done 168
⛳ What we achieved 169
⛳ Flexible retry Combine different retry policies 170
⛳ Predictable Know your errors in advance 171
⛳ Isolated side effects Combine complex tasks without execution 172
Problem - Solution Empty values ➡ 173 Option
Problem - Solution Empty values ➡ Option Exceptions ➡ Try (or Either) 174
Problem - Solution Empty values ➡ Option Exceptions ➡ Try (or Either) Async side effects ➡ Task / TaskEither 175
Remember?
Option Try, Either Task, TaskEither 177
One last thing FP is about composition: Function composition Monadic composition 178
Conclusions 179
One last last thing Composing Software: The Book E. Elliot Functional Programming in Scala P. Chiusano, R. Bjarnason grammarly.com/jobs 180
Developing frontend applications is not simple because crafting UI systems with a complex mutable state spread across the network is inherently difficult. This problem is still very new and thus does not have clear answers. At Grammarly, we have found the methodology that lets us tackle this complexity while keeping our codebase error-free and predictable. Our approach combines the pragmatic usage of functional programming with static typing. I will show you how functional programming can solve typical frontend problems effectively and elegantly.
for free. You
can too.