Other languages already have readable keywords in the function definition; extends, raises, where, having, Optional, and so on. They don’t feel unnecessarily verbose.
Because they’re working on algebraic effects so obviously IO won’t be the only effect out there. Also because “mut” is even more misleading as it doesn’t capture everything an “IO function” can do, in comparison to a pure function.
”mutates IO”? Anything is better than /{}. I don’t know, maybe one gets accustomed to it after a while? It would be rather verbose to write “returns Foo” everywhere. I’m just looking at this with fresh eyes and this aspect of the language is a token-soup. Other parts look neat though.