Why We Rewrote Our Entire Compiler in a Weekend
A cautionary tale about ambition, caffeine, and the seductive power of clean abstractions.
It started with a whiteboard sketch that went too far. My co-founder and I were mapping out the new module resolution system for Mosaic's runtime when she drew a box labeled "just parse it twice" and we both laughed. Three days later, neither of us was laughing.
The Old Architecture Wasn't Broken
That's the part nobody wants to hear. Our original compiler had handled forty million user sessions without a single catastrophic failure. It was ugly — a tangle of regex-based transforms and string concatenation that looked like it had been written during a hackathon, because it had been. But it worked. The problem was that "working" and "understandable by anyone other than its author" are very different things.
"We told ourselves we'd ship the new compiler by Monday. It took three weeks, four existential crises, and one very patient dog."
The rewrite began on a Friday afternoon with the kind of confidence that only comes from having never done something before. We chose Rust for the parser, kept TypeScript for the codegen layer, and drew clean lines between phases that had previously been smeared across a single compile() function.