I mean, the closest I know to avoiding this is something like writing lisp with smartparen. This ensures the code is always syntactically valid, but it doesn't

I mean, the closest I know to avoiding this is something like writing lisp with smartparen. This ensures the code is always syntactically valid, but it doesn't prevent you from partially typed function names like "filte". However, I think that's a good thing. The alternative to partially typing out functions would be selecting them from a list or automatically having the editor fill in the most likely match from before the first letter is typed. Both the latter would, if interrupted, convey less information than the partially typed out name. Phrased differently: writing code will always be a matter of narrowing down the full namespace to the appropriate function. Partially typing it provides the human about the most information on where things are going, even if it's not as friendly on compilers. So yeah, we could have compilers fill in the missing information to create a compiler-valid state from partial information, but what does that give us? A wildly incorrect program that's harder to fix? Programming is writing code for humans that computers occasionally read, not the other way around. With today's focus on tooling, I feel like we have forgotten this.