Rewrite type system of the Ruby compiler
The type system consists out of many ugly hacks that make even Nurgle look pretty. Every time I ran into problems I tried to work around them because I didn't want to rewrite things. However I have now reached a point where this is necessary: initialising generic types is super buggy and there's no easy way around this (other than using explicit type annotations all over the place).
Edited by Yorick Peterse