Monads @ ATLRUG

An introduction to monads for Rubyists, with accompanying code at https://github.com/jamesdabbs/rb-monads

Transcript

1. An Intro to Monads Categories for the Working Programmer James Dabbs jdabbs@emcien.com | github.com/jamesdabbs
2. What Is a Monad?
3. What Is a Monad? Definition 1:
4. What Is a Monad? Definition 1: A monad is a monoid in the category of endofunctors
6. Choosing the right abstraction is the difference between working code and great code.
7. Choosing the right abstraction is the difference between working code and great code. - James Dabbs
8. Well-Abstracted Code is
9. Well-Abstracted Code is Readable
10. Well-Abstracted Code is Readable Testable
11. Well-Abstracted Code is Readable Testable Extensible
12. Well-Abstracted Code is Readable Testable Extensible Maintainable
13. Well-Abstracted Code is Readable Testable Extensible Maintainable Elegant
14. Abstractioneering
15. Abstractioneering Connection details are abstracted out so they can be changed in one place
16. Abstractioneering Connection details are abstracted out so they can be changed in one place The User object encapsulates a user’s behavior
17. Abstractioneering Connection details are abstracted out so they can be changed in one place The User object encapsulates a user’s behavior Separation of data and representation
18. Abstractioneering
19. Abstractioneering
20. Abstractioneering The real value of Rails (or any MV* framework) is in providing a set of useful abstractions to solve common problems and promote code reuse.
21. Abstractioneering The real value of Rails (or any MV* framework) is in providing a set of useful abstractions to solve common problems and promote code reuse. Our goal as software engineers should be to recognize common problems and write reusable abstractions to solve them.
22. Reusing Code
23. Reusing Code Inheritance / subclassing
24. Reusing Code Inheritance / subclassing Modules / mixins
25. Reusing Code Inheritance / subclassing Modules / mixins Object composition / decorators / presenters
26. Reusing Code Inheritance / subclassing Modules / mixins Object composition / decorators / presenters Function composition
27. Reusing Code Inheritance / subclassing Modules / mixins Object composition / decorators / presenters Function composition Monads
28. Reusing Code Inheritance / subclassing Modules / mixins Object composition / decorators / presenters Function composition Monads
29. Reusing Code Inheritance / subclassing Modules / mixins Object composition / decorators / presenters Function composition Monads Object oriented
30. Reusing Code Inheritance / subclassing Modules / mixins Object composition / decorators / presenters Function composition Monads Object oriented Functional
31. Functional Programming
32. Functional Programming Start with functions - these represent actions or behaviors
33. Functional Programming Start with functions - these represent actions or behaviors Build programs by combining simple functions into more complicated ones
34. Functional Programming Start with functions - these represent actions or behaviors Build programs by combining simple functions into more complicated ones Verbs, not nouns
35. Functional Programming
36. Functional Programming Category theory is the mathematical study of functions and composition
37. Functional Programming Category theory is the mathematical study of functions and composition Monads are important objects in category theory
38. Functional Programming Category theory is the mathematical study of functions and composition Monads are important objects in category theory As such, monads tend to be more important and prevalent in strongly functional languages.
39. Functional Programming For instance, Haskell programs can’t do anything without monads
40. Functional Programming A language that doesn't affect the way you think about programming, is not worth knowing. For instance, Haskell programs can’t do anything without monads
41. Functional Programming A language that doesn't affect the way you think about programming, is not worth knowing. - Alan Perlis For instance, Haskell programs can’t do anything without monads
42. Functional Programming Ruby doesn’t have first-class functions, but does support some common functional idioms:
43. Functional Programming In a pure functional language, this construction could look something like
44. Functional Programming In a pure functional language, this construction could look something like
45. Functional Programming In a pure functional language, this construction could look something like Or, simpler
46. Functional Programming In a pure functional language, this construction could look something like Or, simpler
47. Composition This worked out because the types plumbed up nicely
48. Composition This worked out because the types plumbed up nicely What if we aren’t so lucky?
49. Extending Composition
50. Composition Here we have the following types
51. What Is a Monad?
52. What Is a Monad? Definition 2:
53. What Is a Monad? Definition 2: A monad is the glue you need to bind these functions together and “cross-compose”
54. What Is a Monad? Definition 2: A monad is the glue you need to bind these functions together and “cross-compose”
55. What Is a Monad?
56. What Is a Monad? Definition 3:
57. What Is a Monad? Definition 3: A monad is a structure m with two functions*
58. What Is a Monad? Definition 3: A monad is a structure m with two functions*
59. What Is a Monad? Definition 3: A monad is a structure m with two functions* In the case of IO, this becomes
60. What Is a Monad? Definition 3: A monad is a structure m with two functions* In the case of IO, this becomes
61. Monad Laws We need to specify a few restrictions
62. Monad Laws We need to specify a few restrictions
63. Monad Laws We need to specify a few restrictions This bind totally disregards the bound value
64. Monad Laws
65. Monad Laws
66. Monad Laws
67. Monad Laws
68. Monad Laws The last law looks complicated, but that’s because we’re at the wrong level of abstraction. With an appropriate cross-composition operator it’s
69. Monad Laws The last law looks complicated, but that’s because we’re at the wrong level of abstraction. With an appropriate cross-composition operator it’s
70. The Ubiquitous Monad
71. The Ubiquitous Monad IO - as discussed, and hence the do joke
72. The Ubiquitous Monad IO - as discussed, and hence the do joke List - represents non-deterministic (or, with a little modification, probabilistic) computation
73. The Ubiquitous Monad IO - as discussed, and hence the do joke List - represents non-deterministic (or, with a little modification, probabilistic) computation Maybe - represents computation that might fail to return a value
74. The Ubiquitous Monad IO - as discussed, and hence the do joke List - represents non-deterministic (or, with a little modification, probabilistic) computation Maybe - represents computation that might fail to return a value State - functions that alter program state
75. The Ubiquitous Monad IO - as discussed, and hence the do joke List - represents non-deterministic (or, with a little modification, probabilistic) computation Maybe - represents computation that might fail to return a value State - functions that alter program state Persistent - functions that alter a database
76. Examples Refer to console / editor
77. Takeaways
78. Takeaways Monads are a different type of composition, well suited to managing state, history, or side effects
79. Takeaways Monads are a different type of composition, well suited to managing state, history, or side effects Functional programming and category theory are worth studying - especially together
80. Fin Questions?
81. References Source code - https://github.com/jamesdabbs/rb- monads The Kingdom of Nouns - http://steve- yegge.blogspot.com/2006/03/execution-in-kingdom- of-nouns.html Learn You a Haskell - http://learnyouahaskell.com/