How Functional Programming Made Me a Better Developer
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With the rise in popularity recently, functional programming has become ""The Next Big Thing"". As of today, there are tons of frameworks and tools that can be used for front-end, back-end, desktop, and mobile development. With that being said, the majority of us are still using object-oriented languages for our day jobs and don't need to learn functional programming, right? In this talk, I'll walk you through my experiences learning functional programming over the last year, how my style of programming has changed, and how I now think about programming with regards to both functional and object-oriented paradigms.
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How Functional Programming Made Me a Better Developer
- 1. Cameron Presley @pcameronpresley Cameron@TheSoftwareMentor.com How Functional Programming Made Me a Better Developer
- 2. 2 Hello!
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- 5. “ The single responsibility principle states that every module or class should have responsibility over a single part of the functionality provided by the software, and that responsibility should be entirely encapsulated by the class. -Wikipedia 5
- 6. “ The single responsibility principle states that every module or class should have responsibility over a single part of the functionality provided by the software, and that responsibility should be entirely encapsulated by the class. -Wikipedia 6
- 7. What Happens If You Follow SRP to the Extreme? 7
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- 12. Extreme SRP and ISP = lots of fine grain classes 12
- 13. Objects can be thought of data with behavior, but what if we flipped that around? 13
- 14. 14 F#
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- 17. Task Snapper ￮ C# application that grabs a screenshot every so often ￮ Focus on the language, not the problem 17
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- 24. Love Letter ￮ 8 different kinds of cards, each with their own rules ￮ Write more idiomatic fp ￮ No classes or exceptions 24
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- 31. Blackjack! ￮ Still modeling a card game ￮ Something with easier business rules ￮ Already knew the rules 31
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- 33. 33 How would you score a hand in Blackjack? Figure out how many Points each Card is worth Add the Points up
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- 40. 40 different outputs the same output A method, that when given the same two inputs, it returns…
- 41. 41 Methods that always return output solely based on input are known to be pure
- 42. 42 Sound crazy? Elm React with Redux
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- 53. 53 Interfaces are powerful because they enforce a contract at the code level. If the contract isn’t observed, the code won’t compile!
- 54. Given this interface, what should GetById return? Pop Quiz! Anything that implements this interface will always return an Employee object, right?
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- 57. 57 What Happened? Interface said that an Employee will always be returned But sometimes, there won’t be an Employee, so what to return? Compiler can’t enforce that I handle null / exceptions
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- 62. 62 Boundary (data in/out) Business Rules (processing the data) Workflow (combination of both)
- 63. Boundary ￮ Databases, files, APIs ￮ Typically impure ￮ For easier testing of workflows, recommend using an interface ￮ Inspiration from Alistair Cockburn’s Hexagonal Architecture 63
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- 66. Business Rules ￮ Bulk of the application ￮ Purity is key ￮ Remember SOLID when implementing 66
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- 68. Workflows ￮ Combines both Boundary and Business Rule ￮ General shape is: ￮ Data comes in through the boundary ￮ Data is processed by the business rules ￮ Data goes out through the boundary 68
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- 75. 75 References F# • F Sharp for Fun and Profit (https://fsharpforfunandprofit.com) • The Book of F#: Breaking Free with Managed Functional Programming by Dave Fancher • F# Jumpstart (Pluralsight Course) by Kit Eason Functional • Mark Seemann’s blog: (http://blog.ploeh.dk) • Hexagonal Architecture (post) by Alistair Cockburn • Reid Evans YouTube (https://www.youtube.com/channel/UCMxR2KmDlDMEsvfKOjzRNbA) Code • CRUDy : https://github.com/cameronpresley/CRUDy • Optionally: https://github.com/cameronpresley/Optionally
Editor's Notes
- The Road Taken Learning Functional Programming (i.e. What Got Me Started Down This Path?)
- Some SOLID Inspiration SOLID = Mnemonic for software designed By following SOLID we tend to write more maintainable software Want to focus on S (Single Responsibility Principle)
- Lot of small classes with a single public method A lot of ceremony Could use ReSharper or another tool to create the boilerplate, but how about eliminate the need for it?
- Asking the Twitterverse for help
- Like most things in software development, I wasn’t the first to come to this
- Chose F# Familiar with .NET Comfortable with the tooling Community resources
- I worked on/off with functional for a year Lots of heads down, then come up for air for a bit Rinse and repeat Took three attempts for me to really “get” it
- First Attempt!
- Decided to port a C# application (Task Snapper) Grabs a screenshot every so often Idea was to focus on the language, not how to solve the problem
- Defined a type Attached functions to it Some of those functions threw exceptions
- Defined a type Attached functions to it Some of those functions threw exceptions
- Defined a type Attached functions to it Some of those functions threw exceptions
- Defined a type Attached functions to it Some of those functions threw exceptions
- I wrote F# But wrote OO in FP Didn’t really see the point Need to learn more about FP
- Look ma, no exceptions! Learned more about data modeling (making illegal states unrepresentable) Game rules a bit more complicated than expected *Spent a lot of time learning the problem and attempting a solution, not porting
- Modeling Data and State using Discriminated Unions
- Using type aliases
- Making new types out of existing types using records
- No classes, no exceptions!
- 3rd Attempt
- Making Illegal States Unrepresentable
- Modeling how to turn a Card into a
- How to add two points together
- Reflection * Comfortable with handling errors without exceptions Using pattern matching more effectively Working with built-in List operators Map and Reduce Starting to think about how to use these concepts in C#
- Learned all of this cool stuff, how does it affect my coding habits now?
- Code is easy to test implies code is easy to maintain The opposite may hold then, hard to test code may not be maintainable What defines easy to test code?
- What’s easier to test? Which method would be easier to troubleshoot?
- Implies there are no side effects (databases, file systems, apis, etc…) Easiest thing to test because no dependencies are needed
- Elm Architecture (time traveling debugger) React with Redux (reducers)
- Pure because 3 will always return the same value
- Not pure because the API could fail or give me back different values
- Improved LINQ Skills
- When working with lists of data, here’s how I’d used to do it Quickly, what am I trying to do here?
- Before and after The one on the left, I have to keep track of what I’m doing The one on the right, I can trust that LINQ works and I’m plugging my business rules into the correct places
- Designing Interfaces that don’t suck
- Allows us to lean on the compiler
- Why doesn’t this work? Options have no clue about Id, FirstName or LastName
- Pattern match to figure out what to do. Compiler forced us to do that! Win!
- How I build software
- Getting data into the system
- Getting data out of the system
- Learning functional was hard for me Lots of failures, but improved incrementally Made me re-evaluate how I build software Still use functional concepts in my coding Even if I’m not using a functional language