Type-Driven Design: The 'Parse, Don't Validate' Approach to Programming

Historically, I've struggled to find a concise, simple way to explain what it means to practice type-driven design.

The key insight is that parsing transforms unstructured data into structured types, while validation merely checks if data meets certain criteria.

When you parse, you're building a validated-by-construction representation of your data, which eliminates entire classes of runtime errors.

This approach leverages the type system to enforce correctness at compile time rather than discovering errors at runtime.

The 'parse, don't validate' philosophy creates more robust, maintainable code by making invalid states unrepresentable in the type system.