Some middle way between F#/Kotlin and Rust. Sum types, generics etc are completely non-negotiable. Something where I can use a GC for 90% and build regions of h

Some middle way between F#/Kotlin and Rust. Sum types, generics etc are completely non-negotiable. Something where I can use a GC for 90% and build regions of high perf or low level when needed. I want to say “in this region I want zero allocations” and the compiler will warn if an iterator or closure or something ergonomic-but-expensive allocates in that region. This is where CLR/Jvm lands often fail. I even want to be able to get rid of virtual dispatch and all pointer chasing but only for select regions. In some high level languages I can’t tell whether an abstraction comes at a cost. In the bulk of the code I want the syntax to be as terse as possible so the business logic is as clear as possible even if it comes at a perf cost. This is where Rust often fails. The logic of something where I don’t care about perf is obscured by token salad for Box’es and similar.