functional-patterns

name	functional-patterns
description	Higher-order functions, composition, monads, immutability, and functional programming idioms.

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