BM25 is the easy part. It's probably a dozen lines of code, maybe two. The real work is in the design of the index that enables you to write that dead-simple function -- the in-memory data structures, the on-disk data structures, keeping them in sync, fault tolerance, batching, and a bunch of other things.
If you ask Claude to "implement BM25" you will not get what you want. I see a whole lot of this: people that don't know what they're doing get garbage results out of LLMs.
If you ask Claude to "implement BM25" you will not get what you want. I see a whole lot of this: people that don't know what they're doing get garbage results out of LLMs.