In the last 15 mins or so, he shows #programsynthesis using barliman. Test Driven Development, where all you do is write the tests, and the theorem prover writes the code (or you can help it by writing the skeleton of the code). Awesomesauce.
A co-author of "The Reasoned Schemer" talks about the meta-circular evaluator, trees, lists, lambda calculus as the Maxwell's Equation of programming, scaring the veterans of the lambda calculus, mentions in passing delimited continuations, and more.
> The interesting thing here is that even though we've only partially specified this program, we can fail a test.
> The second test fails, and what that's telling us is that there are no expressions, in our subset of Scheme, for which filling in [the placeholders] ,B ,C and ,A would make that test pass.