Slide 1
Slide 1 text
Handling and Composing
side effects
In Clojure
Or how to avoid mud-balls
By Kapil Reddy
Slide 2
Slide 2 text
Principal Engineer @ Helpshift
Clojure
Distributed Systems
Music
Graphic novels
Football
Film and Theatre
Slide 3
Slide 3 text
No content
Slide 4
Slide 4 text
Scale
• 165000 Requests per Second
• @50 ms Response time
• ~400GB data transfer every hour
• 1000+ VMs deployed at peak
Slide 5
Slide 5 text
Journey of a Clojure codebase
Slide 6
Slide 6 text
A simple web app
Slide 7
Slide 7 text
POST /favourites/
Add a song to favourites
Slide 8
Slide 8 text
Request -> Server -> Response
Slide 9
Slide 9 text
Request -> Server -> Response
Slide 10
Slide 10 text
Server
Req -> Handler -> Resp
Slide 11
Slide 11 text
No content
Slide 12
Slide 12 text
No content
Slide 13
Slide 13 text
No content
Slide 14
Slide 14 text
No content
Slide 15
Slide 15 text
No content
Slide 16
Slide 16 text
No content
Slide 17
Slide 17 text
No content
Slide 18
Slide 18 text
No content
Slide 19
Slide 19 text
No content
Slide 20
Slide 20 text
No content
Slide 21
Slide 21 text
{}
Slide 22
Slide 22 text
No content
Slide 23
Slide 23 text
http://blog.fogus.me/2010/09/28/thrush-in-clojure-redux/
Slide 24
Slide 24 text
No content
Slide 25
Slide 25 text
No content
Slide 26
Slide 26 text
No content
Slide 27
Slide 27 text
No content
Slide 28
Slide 28 text
No content
Slide 29
Slide 29 text
No content
Slide 30
Slide 30 text
No content
Slide 31
Slide 31 text
No content
Slide 32
Slide 32 text
No content
Slide 33
Slide 33 text
No content
Slide 34
Slide 34 text
No content
Slide 35
Slide 35 text
No content
Slide 36
Slide 36 text
No content
Slide 37
Slide 37 text
Problems with thrush for side
effects
• Overlapping keys
Slide 38
Slide 38 text
No content
Slide 39
Slide 39 text
Problems with thrush for side
effects
• Overlapping keys
• Shape of data gets complex
Slide 40
Slide 40 text
No content
Slide 41
Slide 41 text
Failures !!!
Slide 42
Slide 42 text
No content
Slide 43
Slide 43 text
No content
Slide 44
Slide 44 text
No content
Slide 45
Slide 45 text
Problems with thrush for side
effects
• Overlapping keys
• Shape of data gets complex
• Handling complex error scenarios
Slide 46
Slide 46 text
Can we do better?
Slide 47
Slide 47 text
No content
Slide 48
Slide 48 text
No content
Slide 49
Slide 49 text
No content
Slide 50
Slide 50 text
No content
Slide 51
Slide 51 text
Great, how do use it?
Slide 52
Slide 52 text
Solution!?
Slide 53
Slide 53 text
Shinri
Slide 54
Slide 54 text
No content
Slide 55
Slide 55 text
No content
Slide 56
Slide 56 text
No content
Slide 57
Slide 57 text
No content
Slide 58
Slide 58 text
No content
Slide 59
Slide 59 text
No content
Slide 60
Slide 60 text
No content
Slide 61
Slide 61 text
Problems with thrush for side
effects
• Overlapping keys
• Shape of data gets complex
• Can’t handle complex failure scenarios
Slide 62
Slide 62 text
Problems with thrush for side
effects
• Overlapping keys
• Shape of data gets complex
• Can’t handle complex failure scenarios
Slide 63
Slide 63 text
No content
Slide 64
Slide 64 text
No content
Slide 65
Slide 65 text
No content
Slide 66
Slide 66 text
No content
Slide 67
Slide 67 text
No content
Slide 68
Slide 68 text
No content
Slide 69
Slide 69 text
No content
Slide 70
Slide 70 text
Problems with thrush for side
effects
• Overlapping keys
• Shape of data gets complex
• Can’t handle complex failure scenarios
Slide 71
Slide 71 text
No content
Slide 72
Slide 72 text
No content
Slide 73
Slide 73 text
No content
Slide 74
Slide 74 text
No content
Slide 75
Slide 75 text
No content
Slide 76
Slide 76 text
No content
Slide 77
Slide 77 text
No content
Slide 78
Slide 78 text
Order is implicit
Slide 79
Slide 79 text
No content
Slide 80
Slide 80 text
No content
Slide 81
Slide 81 text
Self documenting
Slide 82
Slide 82 text
No content
Slide 83
Slide 83 text
Execution and policy
are separate
Slide 84
Slide 84 text
Parallel execution
Slide 85
Slide 85 text
No content
Slide 86
Slide 86 text
No content
Slide 87
Slide 87 text
No content
Slide 88
Slide 88 text
Future
• core.async support
• clojure.spec support
Slide 89
Slide 89 text
Alternatives
• Prismatic Plumbing
• Function lenses
Slide 90
Slide 90 text
Conclusions
• Writing complex side effects code can be tricky
• Thrush is not a good abstraction for side effects
• Graphs are a great way to represent multiple side
effects / computations
• Defining APIs is simple in Clojure
• Libraries like Shinri and Prismatic Plumbing can help
Slide 91
Slide 91 text
Fin