Hi, I Just want to discuss this idea: type instability in functions is a source of slowness, and in fact there are several tools to catch instances of it. I would even say that ising type instability in functions is considered bad style. the most important use case for type instability seems to be allowing a good interactive experience in the Repl. Now since work in the repl is always in global scope I think disabling type instability in functions would not change this interactive experience. Then it would give us several serious advantages:
1. No type instability slowness to chase, a few less tools to maintain 2. Since types in functions are stable, They could be statically type checked just before compilation (not definition). So ifnyou try to run a function that calls some non existent method you'll get an error on compile time I don't like to call julia dynamic, I prefer interactive. And I realise there are many subtleties here and this is really not that easy to implement, but maybe julia could be the first interactive and statically typed language. Hope I'm not being too greedy ;) Also look at the crystal language, they use some techniques similar to those used in julia to do global type inference. They achieve fast compiled programs without ever having to type a thing. And of course you can still get type errors at compile time and some good tooling like statically typed languages. They miss though the interactivity at global scope. Thoughts?
