[roschdal]

Then please answer why Elm was chosen instead of some mainstream programming language/framework. Choosing Elm seems like a very risky choice for something as important as railways.

[Skinney]

Elm is a frontend language. Java works on the backend.

At Vy, Elm is used for frontend, Java and Kotlin for backend.

[roschdal]

This doesn't address the issue of mainstream technology, versus bleeding-edge, obscure, niche technology such as Elm.

Kotlin in the backend isn't a mainstream technology choice either.

[Skinney]

Elm was chosen because we believed it to be a better language than those which are mainstream right now. We believed it would make us more productive, prevent bugs before they reached production, be better at local reasoning and make it easier to onboard new people.

So far we are not dissapointed, and in my opinion Elm is on its way to become mainstream because of these things.