A programming language with the easyness of dealing with state and effects of a mainstream language and with the guarantees you get from a pure functional language
You mean getting the benefits of functional programming without learning functional programming? ;) Once you find a way into it you really see its all "Lego's". You'll get there!
Being legos is fine but monad transformer stacks and free monads are legos that I can't see most coders putting in the yards to understand. But that's the level you need.to get to to do useful stuff, lest you just do everything in IO but that's imperative style really.
I think a great example of what I mean is Linq and async/await in C#.