How FP made Grammarly codebase error-Free & Predictable Anton Pets 1 October 2019
A presentation at Grammarly Meetup in October 2019 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
6
7
Grammarly Challenges 8
Text is difficult 9
Change is difficult ➡ 10
Our combo Object Oriented Design 11
Our combo Object Oriented Design 12
13
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
20
21
22
TypeScript FP libs Funfix fp-ts 23
TypeScript FP libs Funfix fp-ts 24
Functional Programming: Real Life Cases 25
💼 Case 1/4 26
27
28
29
😊 30
🧪 How to experiment ? 31
32
33
34
35
Can we 🧪 better ? 36
37
38
39
40
41
42
43
44
45
Pure Functions Deterministic: Same Input ➡ Same output No uncontrolled side effects 46
Pure Functions Deterministic: Same Input ➡ Same output No uncontrolled side effects 47
48
⛳ What we achieved 49
⛳ Reliable almost nobody knows about 🧪 50
⛳ Extensible add ♾ number of 🧪 51
💼 Case 2/4 52
53
54
55
56
57
🙏 Will not compile 58
🤔 But how to deal with null? 59
60
🤔 Empty alert? Exception? … 61
Bad 62
63
64
65
66
67
68
Option ≡ an array with 0…1 elements 69
map filter forEach contains … 70
map filter forEach contains … empty getOrElse fold … 71
72
73
74
75
⛳ What we achieved 77
⛳ Reliable empty values are safe 78
⛳ Clean no ifs overload, empty values handled separately 79
💼 Case 3/4 80
81
82
83
84
85
86
87
88
89
90
91
🤔 How to handle errors correctly? 94
95
🧐 96
97
98
99
100
⛳ What we achieved 101
⛳ Clean & Confident no defensive programming 102
⛳ Single Responsibility Business logics is separated from error handling 103
💼 Case 4/4 104
105
106
107 🏋
React lazy loading 👍 108
🌓 109
https://dev.to
112
113
114
115
116
117
🤔 How to build a good retry function?
120
121
122
😱 125
126
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
136
✅ 137
☑ ✅ 138
https://github.com/gcanti/retry-ts by the author of fp-ts 139
140
141
142
You can’t just stop speaking about FP
144
146
147
148
149
✅ 150
☑ ✅ ☑ 151
152
153
154
✅ 155 ✅
☑ ✅ ☑ ☑ 156
157
158
159
160
161
✅ 162 ✅ ✅
☑ ☑ ☑ ☑ ✅ 163
164
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
