You could do deriv properly in C if you have support for “blocks”; otherwise you’ll have to store your state in a struct. I really wouldn’t have got this stuff

You could do deriv properly in C if you have support for “blocks”; otherwise you’ll have to store your state in a struct. I really wouldn’t have got this stuff 5 years ago but functions returning functions is a super sweet tool and I’m glad it’s finally seeing mainstream adoption. It’s a small leap from the imperative mindset but results in much neater flows when done well.