I was already writing these comments from time to time to describe the transformations across different lines of a program, now they're actually part of the verification of the function. It's neat! I think I might write a thing about this once it's a bit less clunky.
I've been writing a bit of prolog these days, and the ghc syntax for rules has really grown on me. Enough that I've been using ( a b -: c ) for routines that require validation. Not sure if cute or travesty.