Composing side effects in Clojure

We always end up in a situation where we need to do a bunch of side effects on a user action. This is simple as long as the side effects don’t depend on each other. Errors and unhappy paths make it even harder. The talk presents an approach that tries to solve these problems.

Transcript

1. Handling and Composing side effects In Clojure Or how to avoid mud-balls By Kapil Reddy
2. Principal Engineer @ Helpshift Clojure Distributed Systems Music Graphic novels Football Film and Theatre
4. Scale • 165000 Requests per Second • @50 ms Response time • ~400GB data transfer every hour • 1000+ VMs deployed at peak
5. Journey of a Clojure codebase
6. A simple web app
7. POST /favourites/ Add a song to favourites
8. Request -> Server -> Response
9. Request -> Server -> Response
10. Server Req -> Handler -> Resp
21. {}
23. http://blog.fogus.me/2010/09/28/thrush-in-clojure-redux/
37. Problems with thrush for side effects • Overlapping keys
39. Problems with thrush for side effects • Overlapping keys • Shape of data gets complex
41. Failures !!!
45. Problems with thrush for side effects • Overlapping keys • Shape of data gets complex • Handling complex error scenarios
46. Can we do better?
51. Great, how do use it?
52. Solution!?
53. Shinri
61. Problems with thrush for side effects • Overlapping keys • Shape of data gets complex • Can’t handle complex failure scenarios
62. Problems with thrush for side effects • Overlapping keys • Shape of data gets complex • Can’t handle complex failure scenarios
70. Problems with thrush for side effects • Overlapping keys • Shape of data gets complex • Can’t handle complex failure scenarios
78. Order is implicit
81. Self documenting
83. Execution and policy are separate
84. Parallel execution
88. Future • core.async support • clojure.spec support
89. Alternatives • Prismatic Plumbing • Function lenses
90. 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
91. Fin