# On the Expressive Power of Programming Languages

- Programming language theory!
- When a feature
`F`

is added to a language`L`

, is`L + F`

more expressive than`L`

?- Yes, when
`F`

can’t be written in`L`

using a local transformation, like a macro. - This paper provides a formal/general framework for thinking about this question.
- Something about the Church-Turing hypothesis; not really sure how that’s relevant here.

- Yes, when
- Equality is hard. Are two {functions,closures,crypto implementations} equal?

*Stopped at 23:45*