>If you're writing a CMS/wiki software, it's gonna be pretty straightforward to do.

>If you're working with transactions, trades, contracts etc, it's not.

why not?

what's the difference between those two categories, mentioned in your last two sentences, as far as this argument about illegal states is concerned? not clear to me.

in fact, just a few weeks ago, I saw a video by yaron minsky of jane street about ocaml. the title of it might have been "why ocaml". I know he has a video by that name. just not sure whether that was the one I saw or another one by him.

it can easily be googled.

in that video, he talks a fair amount about how jane street uses ocaml, including on how they use it (including defining types for kinds of business domain data, iirc) to make "invalid states unrepresentable" - in fact, iirc, that was the title of one of the slides of his talk.

i remember that very well because i was kind of impressed by the idea, although i have not checked it out practically myself yet.

but I don't know much about this area, so I'm not saying that either he or you are wrong. just asking for clarification / explanation.

also, trades and transactions seems to be the main area that jane street works in.

edited for spelling/wrong autocorrect:

s/one I show/one I saw/

> why not? what's the difference between those two categories, mentioned in your last two sentences, as far as this argument about illegal states is concerned? not clear to me.

I kinda began my comment with that reason: The difficulty entirely depends on whether discarding the occasional invalid write is possible. If you can simply return an error and ignore the write/transaction, you're golden.

If you can't, it becomes incredibly complicated