Functional Patterns

Using functional programming principles for clearer, more maintainable code.

Context

You are using functional patterns. Understand functional principles and idioms.

Domain Context

• Pure Functions: No side effects; same input → same output
• Composition: Build complex functions from simple ones
• Higher-Order: Functions taking/returning functions
• Immutability: Data doesn't change; create new versions instead
• Monads: Pattern for handling effects (Maybe, Either, IO)

Instructions

1. Prefer Pure Functions: Write functions without side effects
2. Compose Functions: Chain simple functions together
3. Use Higher-Order: Map, filter, fold; powerful abstractions
4. Embrace Immutability: Don't mutate; create new values
5. Handle Effects: Use monads or similar for side effects
6. Test Easily: Pure functions are trivial to test

Anti-Patterns

• Treating FP as dogma; some problems need mutation
• Immutability everywhere killing performance; profile before pessimizing
• Monads without understanding; they're useful but not required
• Chaining operations so deeply it's unreadable; readability matters
• Avoiding mutation for simple local data; FP isn't a religion

Further Reading

• Richard Bird & Philip Wadler, Introduction to Functional Programming
• Evan Czaplicki, Elm guide (great FP introduction)
• Brian Lonsdorf, Mostly Adequate Guide to FP