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> When an unexpected state is encountered, instead of either killing the entire process or trying to proceed and risking corruption, you just roll back to a known good state, at the most granular level possible.

> but only Erlang/BEAM made it a first-class concept in a production system.

Exceptions?

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In most languages that have exceptions you don't have the same guarantees because the values are not immutable so if they were mutated they will stay mutated. The language can roll back the stack using exceptions but it can't roll back the state.

The BEAM runtime and all languages that target it including Erlang do not allow mutation, (ETS and company excepted). This means that on the BEAM runtime you can not only roll back the stack but you can also rollback the state safely. This is part of what the poster meant by the most granular level possible.

Can you explain how exceptions (partial stack unwinding while carrying a value) do this?

Maybe their idea is that you can have a thread that processes work from a queue and catch any exceptions thrown during that processing and just continue processing other work.

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