[xyzzyz]

What you describe using many completely unnecessary mathematical terms is not only not found in “every real-world protocol”, but in fact is something virtually absent from overwhelming majority of actually used protocols, with a notable exception of the kind of protocol that gets a four digit numbered RFC document that describes it. Believe it or not, but in the software industry, nobody is defining a new “version number” with “strictly defined algebra” when they want to add a new field to an communication protocol between two internal backend services.

[instig007]

> What you describe using many completely unnecessary mathematical terms

Unnecessary for you, surely.

> Believe it or not, but in the software industry, nobody is defining a new “version number” with “strictly defined algebra” when they want to add a new field to an communication protocol between two internal backend services.

Name a protocol that doesn't have a respective version number, or without the defined algebra in terms of the associated spec clarifications that accompany the new version. The word "strictly" in "strictly defined algebra" has to do with the fact that you cannot evolve a protocol without strictly publishing the changed spec, that is you're strictly obliged to publish a spec, even the loosely defined one, with lots of omissions and zero-values. That's the inferior algebra for protobuf, but you can think it is unnecessary and doesn't exist.

[tptacek]

Instead of just handwaving about whether it's necessary or not, why not point to any protocol that relies on that attribute, and we can then evaluate how important that protocol is?

[porridgeraisin]

Yeah. And for anyone curious about the actual content hidden under the jargon-kludge-FP-nerd parent comment, here's my attempt at deciphering it.

They seem to be saying that you have to publish code that can change a type from schema A to schema B... And back, whenever you make a schema B. This is the "algebra". The "and back" part makes it bijective. You do this at the level of your core primitive types so that it's reused everywhere. This is what they meant by "pervasive" and it ties into the whole symmetric groups thing.

Finally, it seems like when you're making a lossy change, where a bijection isn't possible, they want you to make it incompatible. i.e, if you replaced address with city, then you cannot decode the message in code that expects address.