EH21 - Functional correctness -- Haskell-ing your way to reliable code

Pure functions map the same input to the same output every time, without side effects or mutable state, making code easier to reason about and verify

Small, composable functions that can be verified independently make code more reliable and maintainable compared to large, complex functions

Strong type systems help catch errors at compile time rather than runtime, especially when custom types are used to make invalid states unrepresentable

Declarative programming style focuses on describing what code should do rather than how, similar to mathematical definitions, making verification easier

Avoiding mutable state and side effects helps prevent bugs from functions unexpectedly interfering with each other

Separating pure functions from impure ones that interact with the real world (I/O, databases, etc.) helps contain complexity

Fearless refactoring is enabled by pure functions and strong types since the compiler catches mistakes

Concepts from functional programming like purity and types can be beneficial even when using other languages

Writing many small, pure functions that can be composed together helps build reliable software from verifiable pieces

The compiler acts as documentation enforcer through type signatures, ensuring functions are used correctly