Could Odin have an actual 'function' as part of its syntax?

[floorpigeon]

I like that Odin is more mathematically accurate to its imperative approach by calling subroutines 'proc', but I was thinking, could Odin add a more limited 'func' keyword or something similar that prohibits mutation of state and side effects? I think this would improve visual clarity by making it clear what procedures are purely functional. May be similar to #3600.