Bootstrapping a language can be immensely satisfying.
I've added the ability to define stub types in the Garden stdlib and suddenly I don't need to special-case Int or String! They're just normal type declarations.
Playing with optional type signatures in Python, I realise that the return type is the most important to me.
I'd much rather have a function with only a return type instead of a function with only parameter types. It's often quick to add too.
I've started keeping a list of particularly interesting bugs and patches that I've worked on: https://github.com/Wilfred/interesting-code
The time that I once removed *a single closing paren* in Emacs is still my favourite.
