Can't break be simulated by something like MaybeT? And forWithBreakM :: [a] -> (a -> m (Maybe b)) -> m [b] that stops when f yields Nothing? (isn't this actually sequence . forM?)
Yeah, there are transformations that we could apply to the code to make it work. But those transformations aren't trivial in the general case: how about breaking out of multiple loops or returns out of the function from inside loops? At some point, the transformations that we'd have to do would get so complex they'd hinder the programmer's mental model of what code will get generated. We'd also have to do a fair bit of work to make sure the optimizer can figure out what we're encoding so as to not lose performance.