How FP made Grammarly codebase error-Free & Predictable

How FP made Grammarly codebase error-Free & Predictable Anton Pets 20 July 2019

!” Grammarly - a writing assistant that helps make your communication clear and effective, wherever you type. 20M Daily Active Users !3

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Grammarly Challenges !5

Text is difficult !6

Change is difficult ➡ !7

Our combo Object Oriented Design !8

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We believe that static types help a lot when building a complex system !10

TypeScript is… Args validation - free & out of the box !11

TypeScript is… !12

TypeScript is… 💚 !13

TypeScript is… Confident refactoring !14

TypeScript is… Interfaces! !15

= ❤ Types + !16

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TypeScript FP libs Funfix fp-ts !20

TypeScript FP libs Funfix fp-ts !21

Functional Programming: Real Life Cases !22

💼 Case 1/4 !23

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😊 !27

🧪 How to experiment ? !28

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Can we 🧪 better ? !33

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Pure Functions Deterministic: Same Input ➡ Same output No uncontrolled side effects !43

Pure Functions Deterministic: Same Input ➡ Same output No uncontrolled side effects !44

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⛳ What we achieved !46

⛳ Reliable almost nobody knows about 🧪 !47

⛳ Extensible add ♾ number of 🧪 !48

💼 Case 2/4 !49

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🙏 Will not compile !55

🤔 But how to deal with null? !56

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🤔 Empty alert? Exception? … !58

Bad !59

Null 2) Undefined

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Option ≡ an array with 0…1 elements !66

map filter forEach contains … !67

map filter forEach contains … empty getOrElse fold … !68

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⛳ What we achieved !74

⛳ Reliable empty values are safe !75

⛳ Clean no ifs overload, empty values handled separately !76

💼 Case 3/4 !77

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🤔 ” How to handle errors correctly? !91

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🧐 !93

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⛳ What we achieved !98

⛳ Clean & Confident no defensive programming !99

⛳ Single Responsibility Business logics is separated from error handling !100

💼 Case 4/4 !101

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React lazy loading 👍 !105

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https://dev.to

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What we want? When we want it? Good retry function! Now!!!

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😱 !120

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fp-ts !122

Promise in FP Task !123

Promise in FP Task !124

Promise in FP Task !125

Error + Result container Either<Error, Result> !126

Error + Result container Either<Error, Result> !127

Error + Result container Either<Error, React.Component> where type Error = TimeoutError | 404Error !128

Task returning Either Task<Either<Error, Result>> alias: TaskEither<Error, Result> !129

Task returning Either TaskEither<Error, Result> () => Promise< Either<Error, Result> > !130

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✅ !132

☑ ✅ !133

https://github.com/gcanti/retry-ts by the author of fp-ts !134

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You can’t just stop speaking about FP

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☑ ✅ ☑ ☑ !151

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☑ ☑ ☑ ☑ ✅ !158

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Сode examples: done !163

⛳ What we achieved !164

⛳ Flexible retry Combine different retry policies !165

⛳ Predictable Know your errors in advance !166

⛳ Isolated side effects Combine complex tasks without execution !167

Problem - Solution Empty values ➡ !168 Option

Problem - Solution Empty values ➡ Option Exceptions ➡ Try !169

Problem - Solution Empty values ➡ Option Exceptions ➡ Try Async side effects ➡ Task / TaskEither !170

Remember?

Option Try Task / TaskEither !172

One last thing FP is about composition: Function composition Monadic composition !173

Conclusions !174

One last last thing Composing Software: The Book E. Elliot Functional Programming in Scala P. Chiusano, R. Bjarnason www.grammarly.com/jobs You know what to do !175