Use when writing functional-style code or reviewing for FP cleanliness. Triggers on prompts about pure functions, immutability, function composition, module-level functions, explicit context passing, avoiding inheritance, or stateless designs, even when the user doesn't say 'FP' or 'functional'.
Use when writing functional-style code or reviewing for FP cleanliness. Triggers on prompts about pure functions, immutability, function composition, module-level functions, explicit context passing, avoiding inheritance, or stateless designs, even when the user doesn't say 'FP' or 'functional'.
General Functional Programming Guidelines
Core principles
Prefer module-level functions over classes; pass context explicitly; avoid inheritance.
Favor immutable data and pure functions; no global or shared mutable state.
Compose complex behavior from small, focused functions.
Order pattern matching from most specific to most general.
Gotchas
Most language map/filter are eager, not lazy — chaining many of them allocates intermediate arrays; use generators / streams for large data
Closures over mutable state look pure but aren't — referential transparency requires both inputs and captured environment to be immutable
Partial application order matters — flip exists because curry direction is opinionated, not arbitrary
Promise/IO/effects compose differently from pure values — naïve map over them runs the effect, not the value
