I think you're completely right with this observation. In practice much of Julia is duck typed. It uses types to pass information from the outermost caller to t

I think you're completely right with this observation. In practice much of Julia is duck typed. It uses types to pass information from the outermost caller to the compiler of the inner functions, not to express invariants. Human annotations get in the way of that, and thus get in the way of composability. You want to annotate Interfaces in Julia, not types. But we don't have interfaces.