Haha as someone who has worked in one of these domains using FP even - I wish the people in charge agreed with you!
Reliability is a cost center and Product-oriented Builders treat it as such.
Part of why I like “make invalid states unrepresentable” approaches is exactly that: it’s one of the few reliability investments that can pay back during feature work (safer refactors, fewer regressions), not only during incidents.
and this company is hugely successful. so i've learned that the biggest competitive advantage in fintech is flagrant disregard for correctness and compliance.
i'm glad i have a csuite with the stones to execute that. i am way too principled.
There are constant data bugs in the feeds provided by major exchanges, market makers, etc, and so many iffy business rules that are basically all encoded in 100+ tab excel sheets.
Maybe this article focuses on a very specific niche of banking, but most of it is tied together with FTP and excel sheets.
I think the author would be shocked just how flaky a fundamental banking protocol like SWIFT is.
That’s exactly why I argue for stronger internal modeling: when the boundary is dirty, explicit state machines/ADTs + exhaustiveness + idempotency/reconciliation help ensure bad feeds don’t silently create invalid internal states.
I can understand treating social network sites as less critical, of course.
The reason money-related systems often get singled out is the combination of irreversibility and auditability: a bad state transition can mean incorrect balances/settlement, messy reconciliation, regulatory reporting, and long-tail customer harm that persists after the outage is over.
That said, my point isn’t “finance is special therefore FP.” It’s “build resilience and correctness by design early”, explicit state machines/invariants, idempotency/reconciliation, and making invalid states hard to represent. Doing this from the beginning also improves the developer experience: safer refactors, clearer reviews, fewer ‘tribal knowledge’ bugs.
In other areas like lost sales or failures of the system there is lot more arguments. On other hand if you are rich enough and can prove the other side is off by sufficiently large amount of money you can bring the hammer down with facts.