How FP Made Grammarly’s Codebase Error-Free and Predictable Anton Pets @oopets 7 March 2020
A presentation at Projector Frontend Lectorium in March 2020 in Kyiv, Ukraine, 02000 by Anton Pets
How FP Made Grammarly’s Codebase Error-Free and Predictable Anton Pets @oopets 7 March 2020
Grammarly - a writing assistant that helps make your communication clear and effective, wherever you type. 3
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Grammarly Challenges 5
Text is difficult 6
Change is difficult ➡ 7
Our combo Object Oriented Design 8
Our combo Object Oriented Design 9
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TypeScript is… Args validation - free & out of the box 11
TypeScript is… Args validation - free & out of the box 12
TypeScript is… 13
TypeScript is… 💚 14
TypeScript is… Confident refactoring 15
TypeScript is… Interfaces! 16
TypeScript is… Interfaces! 17
= ❤ Types + 18
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TypeScript FP libs Funfix fp-ts 21
Functional Programming: Real-Life Cases 22
💼 Case 1/4 23
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🧪 How to experiment? 27
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🤔 Can we 🧪 better ? 32
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Immutability 39
Pure Functions Deterministic: Same Input ➡ Same output No uncontrolled side effects 40
Pure Functions Deterministic: Same Input ➡ Same output No uncontrolled side effects 41
Pure Functions 42
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What we achieved ⛳ Reliable Almost nobody knows about 🧪 ⛳ Extensible Add ♾ number of 🧪 44
💼 Case 2/4 45
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🙏 Will not compile 50
🤔 But how to deal with null? 51
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🤔 Empty alert? Exception? … 53
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Option ≡ an array with 0…1 elements 60
map filter forEach contains … empty getOrElse fold … 61
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What we achieved ⛳ Reliable Empty values are safe ⛳ Clean No ifs overload, empty values handled separately 65
💼 Case 3/4 66
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🤔 How to handle errors correctly? 79
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What we achieved ⛳ Clean & Confident No defensive programming ⛳ Singe Responsibility Business logics is separated from error handling 85
💼 Case 4/4 86
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React lazy loading 👍 90
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https://dev.to
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🤔 How to build a good retry function?
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Lets check github.com/gcanti/fp-ts 109
Promise in FP Task 110
Promise in FP Task 111
Promise in FP Task 112
Error + Result container Either<Error, Result> 113
Error + Result container Either<Error, Result> 114
Error + Result container Either<Error, React.Component> where type Error = TimeoutError | 404Error 115
Task returning Either Task<Either<Error, Result>> alias: TaskEither<Error, Result> 116
Task returning Either TaskEither<Error, Result> () => Promise< Either<Error, Result> > 117
✅ 118
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github.com/gcanti/retry-ts by the author of fp-ts 120
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You can’t just stop speaking about FP
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☑ ✅ ☑ 131
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☑ ☑ ☑ ☑ ✅ 141
Сode examples: done 146
What we achieved ⛳ Flexible Combine different retry policies ⛳ Predictable Know your errors in advance ⛳ Isolated side effects Combine complex tasks without execution 147
Problem - Solution Empty values ➡ 148 Option
Problem - Solution Empty values ➡ Option Exceptions ➡ Try (or Either) 149
Problem - Solution Empty values ➡ Option Exceptions ➡ Try (or Either) Async side effects ➡ Task / TaskEither 150
Remember?
Option Try, Either Task, TaskEither 152
One last thing FP is about composition: Function composition Monadic composition 153
Conclusions Twitter: @oopets 154
The last thing Composing Software: The Book E. Elliot Functional Programming in Scala P. Chiusano, R. Bjarnason Blog: https://dev.to/gcanti (fp-ts) 155
