Many of the other languages in the formally verified/dependent type space are academic, but there's government interest in things like Ada too because they don't want their planes to crash. Couldn't say how good its error messages are though.
I've seriously used Erlang for a while, and Haskell looks kinda similar. Ingenious ideas there, cool features, but in the end it's cumbersome to use. So I can see why these are niche and wouldn't consider them next to big ones like Swift or C++.
Many of the other languages in the formally verified/dependent type space are academic, but there's government interest in things like Ada too because they don't want their planes to crash. Couldn't say how good its error messages are though.