Why My Regex-Based Parser Failed and How LLM Function Calling Saved Me

I have a confession: I once spent three full days writing regular expressions to parse doctor’s appointment emails from different providers. By the end, I had a 400-line monstrosity that worked for exactly two email formats. When a third clinic joined the system, I knew it was time for a different approach. The Problem: Unstructured Text Everywhere I was building a small integration that needed to extract structured data—dates, times, names, and addresses—from plain text messages. Th...